Showing papers in "Journal of Experimental Zoology in 1993"
TL;DR: The lipid phase behavior was consistent with the temperature range over which cooling was damaging for pig and shrimp sperm, and the with the extent of damage produced in pig and human sperm, the first direct evidence that cold shock results from lipid phase transitions in cell membranes.
Abstract: When cells are cooled to temperatures above the freezing point of water at rates greater than a few degrees per minute, they sustain irreversible injury. Reduction of this "cold shock" damage could increase the survival of animals and plants at low environmental temperatures and improve the cryopreservation of plant and animal cells. Leakage of solutes across membranes, associated with thermotropic phase transitions in membrane lipids, is thought to be responsible, but this hypothesis has not been tested directly. Using Fourier transform infrared spectroscopy (FTIR), we measured the lipid phase transitions in intact, living sperm, the animal cell in which cold shock has been studied most extensively. A shift in the CH2 absorbance peaks indicates the transition from liquid-crystalline to gel phase. The phase transition in sperm membranes occurred at a lower temperature for a marine shrimp than for the pig. In each case, potassium leakage, which is a hallmark of cold shock damage, increased abruptly near the end of the phase transition. Human sperm are quite resistant to cold shock, and an abrupt lipid phase transition was not detected. This phase behavior is typical of membranes containing a high proportion of cholesterol, and human sperm have an unusually high sterol content. High cholesterol levels are known to stabilize membranes during cooling. Overall, the lipid phase behavior was consistent with the temperature range over which cooling was damaging for pig and shrimp sperm, and the with the extent of damage produced in pig and human sperm. This is the first direct evidence that cold shock results from lipid phase transitions in cell membranes.
546 citations
TL;DR: The whole phenomenon of decidualization which is normally triggered by the embryo can be artificially induced in pseudo-pregnant or hormonally-prepared animals with the use of diverse stimuli.
Abstract: This article reviews the main events of embryo-implantation and decidualization in rodents. In common laboratory rodents the embryo attaches to the uterine epithelial lining, usually on days 4 to 6 of pregnancy. A progressive degree of proximity between trophoblast and epithelium occurs until the epithelial cells undergo apoptosis and detach from the basement membrane. During the attachment stage, the spindle-shaped connective tissue cells that underlie the epithelium next to the embryos transform into polyhedral and closely packed decidual cells. Following the epithelial detachment and the breaching of the basement membrane the embryo is thus in direct contact with decidual cells. These cells accumulate organelles associated with synthesis of macro-molecules, intermediate filaments, and eventually lipid droplets and glycogen. Another remarkable feature of decidual cells is the establishment of gap and adherens intercellular junctions. Differentiation of fibroblasts into decidual cells advances antimesometrially and mesometrially, creating in the endometrium several regions of cells with different morphology. The whole phenomenon of decidualization which is normally triggered by the embryo can be artificially induced in pseudo-pregnant or hormonally-prepared animals with the use of diverse stimuli. The uterine epithelium is probably responsible for the transduction of the initial stimulus. Prostaglandins have been shown to be important in the induction of decidualization. More recently other substances such as leukotrienes, platelet-activating factor (PAF), and transforming growth factor (TGF) have been thought to play a role in induction. Much evidence points to prostaglandin production by the decidual cells. New proteins such as a luteotropic factor, desmin, and other molecules were shown to be produced after rat stromal cells undergo decidual transformation. The extracellular matrix of the mouse decidua contains very thick collagen fibrils. Mouse decidual cells are also very active in phagocytosing the thick fibrils, contributing to the remodeling and involution of the decidua that accompanies embryonic growth. Radioautographic data indicates that mouse decidual cells produce and secrete collagen and sulfated proteoglycans.
308 citations
TL;DR: By observing numerous living eggs from the lesser spotted dogfish Scyliorhinus canicula (L.) caught near Roscoff and reared at recorded temperatures as they developed from first cleavage to hatching, the first reasonably complete developmental table was worked out for this classical material in vertebrate embryology.
Abstract: By observing numerous living eggs from the lesser spotted dogfish Scyliorhinus canicula (L.) caught near Roscoff (France) and reared at recorded temperatures as they developed from first cleavage to hatching, the first reasonably complete developmental table was worked out for this classical material in vertebrate embryology. The successive stages, described and numbered from 1 to 34, correct and replace the incomplete stages A–Q proposed by Balfour (J.Anat. Physiol., 10:555–576,1876) and other even less complete series later published, and is unique in the inclusion of a timetable at 16°C. The stages can be identified, usually through the cleared eggshell wall, with naked eye or low magnification. This table of normal stages of Scyliorhinus can be adapted with slight modification to other chondrichthyan fishes. © 1993 Wiley-Liss, Inc.
294 citations
TL;DR: Interestingly, recent data show that a substantial number of differentiation parameters of these cells change in addition, which suggests interesting new aspects of the basis of steroid hormone action at the endometrium, as well as of trophoblast invasiveness, possibly involving switches in the activity of regulatory "master" genes as are also involved in decision making during development.
Abstract: Implantation initiation in eutherian mammals requires, at least in invasive types of implantation, that 1) the trophoblast or subpopulations of it have reached a state of "invasiveness" and, synchronously, 2) the endometrium has reached a state of "receptivity" ("implantation window"). The cell biological basis of "receptivity" as well as of "invasiveness" has long remained unknown, but recently it appears that the application of modern concepts of cell and developmental biology is opening new views of it, concentrating on cell adhesion and cell polarity phenomena. Implantation initiation requires that the trophoblast attaches via its apical plasma membrane to the apical plasma membrane of the uterine epithelium. Since apical plasma membranes of epithelia are normally non-adhesive, this represents a cell biological paradox. In development, cells can express two major phenotypes and switch between these: 1) the mesenchymal/fibroblastoid phenotype that is compatible with cells moving individually; 2) the epithelioid phenotype which is characterized by cells expressing apico-basal polarity and a strong association with neighbouring cells via various junctions, so that they can migrate as sheets but not as individual cells. Application of this concept to embryo implantation would seem to lead to the hypothesis that the trophoblast of blastocysts has to give up part of its typical epithelial organization when becoming invasive; it must express cell-cell adhesion molecules or matrix receptors non-typically at its apical plasma membrane, change the spectrum of expressed adhesion molecules, and alter its motility apparatus. This applies in a somewhat similar way to the uterine epithelium at "receptivity". Interestingly, recent data show that a substantial number of differentiation parameters of these cells change in addition. It appears that part of the epithelial differentiation program is down-regulated at this phase. This also suggests interesting new aspects of the basis of steroid hormone action at the endometrium, as well as of trophoblast invasiveness, possibly involving switches in the activity of regulatory "master" genes as are also involved in decision making during development.
235 citations
TL;DR: In many species the uterus undergoes histological changes and secretes increased amounts of protein, yet the authors still do not understand the role, if any, these proteins play in initiating renewed embryonic development, and the phenomenon of embryonic diapause still holds many mysteries for scientists to solve.
Abstract: Embryonic diapause occurs in many species of vertebrates, but the physiological mechanisms which control this fascinating process are exceedingly different in the diverse groups which employ this reproductive strategy. In nonmammalian species and some bats, reduction in rate of embryonic development is temperature dependent, but this is not the case in most mammals. Development becomes arrested at the blastocyst stage of embryogenesis in mammals which exhibit delayed implantation, whereas postimplantation development is continuous but retarded in species exhibiting delayed development. The hormonal control of diapause is remarkably different in the various species. Pituitary secretion of prolactin prevents implantation in the tammar wallaby but hastens renewed development and implantation in the mink and spotted skunk. Ovariectomy results in the eventual death of blastocysts in mustelids but induces renewed development and implantation in the armadillo. Luteal function, as evidenced by elevated progesterone secretion, is essentially constant in the roe deer and armadillo, whereas the luteal cells fail to complete their differentiation and secrete low levels of progesterone in carnivores. Progesterone will induce implantation in the tammar wallaby, but estrogen is required to induce renewed development and implantation in rodents. Neither progesterone and/or estrogens appear to be capable of stimulating implantation in carnivores. The uterus plays an important role in maintaining the embryos in a viable state throughout the period of diapause. In many species the uterus undergoes histological changes and secretes increased amounts of protein, yet we still do not understand the role, if any, these proteins play in initiating renewed embryonic development. Thus the phenomenon of embryonic diapause still holds many mysteries for scientists to solve. © 1993 Wiley-Liss, Inc.
183 citations
TL;DR: Phylogenetic analyses suggest that placental organs have originated on more than 100 occasions among squamate reptiles, and indicate that three separate lineages have converged on substantial placentotrophy through the evolution of specialized histotrophic placentae.
Abstract: Allantoplacentae in lizards and snakes form during the evolution of viviparity through apposition of the chorioallantois and a vestige of the shell membrane to the uterine lining. Generalized squamate allantoplacentae are epitheliochorial, diffuse, adeciduate, and highly vascular, accomplish maternal-fetal gas exchange, and possibly transfer small quantities of organic and inorganic nutrients. Placental gas exchange presumably is enhanced by the thinning of tissues lying between fetal and maternal capillaries, a progressive increase in placental vascularity, and in some species, by differences in oxygen affinity of fetal and maternal blood. A few saurian genera (e.g., Chalcides, Mabuya, and Pseudemoia) include species with specialized placentae that transfer large quantities of nutrients. Specializations of the allantoplacentae of these lizards include interdigitating, hypertrophied uterine and chorioallantoic tissues, and enlarged absorptive chorionic epithelia. South American Mabuya are further specialized by the presence of chorionic areolae and a distinctive placentome. Weekes' 1935 classification of placental morphotypes is reviewed, and a few minor modifications are proposed, in addition to recognition of a fourth morphotype. Phylogenetic analyses suggest that placental organs have originated on more than 100 occasions among squamate reptiles, and indicate that three separate lineages have converged on substantial placentotrophy through the evolution of specialized histotrophic placentae. © 1993 Wiley-Liss, Inc.
170 citations
TL;DR: It is revealed that the ingression of cardiogenic cells through the primitive streak occurs prior to late gastrula stages, suggesting that contributions of epiblast to the heart at later stages are artifactual.
Abstract: A prospective fate map of the avian epiblast at late gastrula and early neurula stages has been generated through the construction of quail/chick transplantation chimeras. This map shows the subdivisions of the prospective ectoderm, mesoderm, and endoderm, both within the epiblast prior to their ingression and within the primitive streak. The map demarcates the locations and extents of the prospective surface ectoderm, otic placodes, neural crest, and neural plate-including its postnodal levels—in prospective ectoderm of the epiblast; prospective foregut, within the prospective endoderm of the epiblast and primitive streak; and prospective notochord, somites, intermediate mesoderm, lateral plate mesoderm, and extraembryonic mesoderm in the prospective mesoderm of the epiblast and/or primitive streak. Prospective cardiogenic cells are apparently absent from the primitive streak at these stages, and contributions of the epiblast to the heart are relatively scant and inconsistent with the expected timing and directions of migrations of prospective cardiogenic cells. Mapping of the primitive streak at earlier stages in another study (Garcia-Martinez and Schoenwolf: Developmental Biology, in press) reveals that the ingression of cardiogenic cells through the primitive streak occurs prior to late gastrula stages, suggesting that contributions of epiblast to the heart at later stages are artifactual. Tests of prospective potency, based on the projected locations of origin of various cell groups provided by the new prospective fate map, are underway. © 1993 wiley-Liss, Inc.
143 citations
TL;DR: A survey of the morphology of the brains of 13 species of decapods shows that all have common areas of neuropil that are developed to differing degrees in the different groups, but the neuropils of the paired accessory lobes appear to have evolved de novo in the Reptantia.
Abstract: A survey of the morphology of the brains (cerebral ganglia) of 13 species of decapods shows that all have common areas of neuropil that are developed to differing degrees in the different groups. The neuropils of the paired accessory lobes, however, appear to have evolved de novo in the Reptantia. Phylogenetic relationships within the Reptantia suggest that the accessory lobes were initially large but became reduced in size during the evolution of the brachyurans and anomalans. © 1993 Wiley-Liss, Inc.
137 citations
TL;DR: Results show that Ta and food availability are effective in modifying both seasonal timing and extent of photoperiodically controlled adaptations, and indicates that Djungarian hamsters are capable of flexible physiological responses towards unpredictable climatic changes in the environment.
Abstract: We investigated the influence of ambient temperature (Ta) and food availability on seasonal timing and extent of physiological responses to short photoperiod (SP), in particular daily torpor, in Djungarian hamsters (Phodopus sungorus). Exposure of hamsters to cold temperature (Ta = 5 degrees C), relative to warm Ta (23 degrees C), resulted in: 1) a significant advance (P < 0.05) of the first occurrence of torpor among cold-exposed hamsters (days 52-97 vs. days 83-99 in SP); 2) a higher (P < 0.01) incidence of torpor (48% vs. 20% torpid animals/day); 3) a higher (P < 0.05) degree of molt into the winter pelt; and 4) an accelerated reduction of body weights (P < 0.001). However, within SP/cold-Ta exposed groups, individual hamsters clearly showed different tendencies for torpor (torpor on 0-95% of days observed). Therefore, we evaluated the effects of small changes in Ta on torpor frequency and extension by subjecting the same SP-adapted individuals to varying temperatures. Lowering of Ta from 15 degrees C to 10 degrees C and 5 degrees C caused significant (P < 0.05) increases in the incidence of torpor (20%, 33%, and 40%, respectively) and lower minimal body temperatures during hypothermia (P < 0.05). When the same animals were subjected to 24-48 h lasting periods of food restriction (60% of the ad libitum intake), torpor frequency further increased 1.8- to 2.6-fold at all Tas. These results show that Ta and food availability are effective in modifying both seasonal timing and extent of photoperiodically controlled adaptations. This integration of multiple environmental cues, combined with a pronounced within-species variability of winter adjustments, indicates that Djungarian hamsters are capable of flexible physiological responses towards unpredictable climatic changes in the environment.
123 citations
TL;DR: The actions of B in these experiments closely resemble those observed with administration of thyroid hormones, suggesting that steroids may interact with endogenous thyroid hormones.
Abstract: The effects of temperature and steroids [testosterone (T), estradiol (E2), and cortico-sterone (B)] on premetamorphic growth and development were investigated in the toad (Bufo boreas). The effects of steroids were both temperature and age dependent. In the first experiment, steroids (1.1–1.4 μM) were administered by dissolving them in the water beginning 1 day after hatching at 22°C or 27°C. At 22°C, B inhibited growth (P 0.05), but T induced early foreleg emergence (FLE) (P < 0.005). At 27°C, B was fatal after 2 weeks of treatment, and T and E2 inhibited growth (P < 0.001) and development (P < 0.001), but did not affect time to FLE.
In a second experiment at 27°C, treatment with 1.1 μM B starting 15 days after hatching induced early metamorphic events (P < 0.001), such as tail resorption and emergence of the left foreleg (but not the right), but jaw and head restructuring failed to occur. All B-treated animals died before complete tail resorption. © 1993 Wiley-Liss, Inc.
In a third experiment, 0.275 and 1.11 μM B, starting at day 43 (stage 43), induced early FLE (P 0.05). Animals in this experiment survived to complete tail resorption and transformed normally. The actions of B in these experiments closely resemble those observed with administration of thyroid hormones, suggesting that steroids may interact with endogenous thyroid hormones.
118 citations
TL;DR: A role for 5-HT in regulating reproduction inZebra mussels is supported and conditions by which zebra mussel spawning may be stimulated or inhibited are defined.
Abstract: The zebra mussel, Dreissena polymorpha, was recently introduced accidentally into the Great Lakes and, due in part to its prodigious reproductive capacity, is spreading rapidly in temperate fresh waters of North America The present studies examine some of the mechanisms that regulate spawning in this animal In August and September 1990 and in May 1991 injection of serotonin (5-hydroxytryptamine, 5-HT) induced ripe male, but not female, zebra mussels to spawn During mid-summer 1991, 5-HT induced spawning in both males and females, and 5-HT could produce spawning responses by either injection or external application External pH over a broad range (60 to 91) had no effect on spawning, neither inhibiting induction of spawning by 5-HT nor significantly eliciting spawning itself With external application, 10(-3) M and 10(-4) M 5-HT caused spawning, but 10(-5) M and 10(-6) M did not Cyproheptadine, a 5-HT receptor antagonist, reduced the response of both males and females by more than half Spawning in response to 5-HT was blocked at 4 degrees C, but not at 12 degrees C, 20 degrees C, or 27 degrees C For male zebra mussels morphological criteria for judging gonadal maturity were well-correlated with probability of spawning in response to 5-HT For females, the likelihood of spawning in response to 5-HT was not tightly coupled to morphological maturity of the gonad, with many morphologically ripe females failing to spawn and some apparently immature animals releasing oocytes Prior spawning reduced subsequent responsiveness and intensity of spawning of animals to 5-HT These experiments support a role for 5-HT in regulating reproduction in zebra mussels and help define conditions by which zebra mussel spawning may be stimulated or inhibited
TL;DR: The conclusion, based on known factors for the species examined, is that both modes of osmotic regulation in hyporegulating marine teleosts and in ureotelic elasmobranchs are about equally efficient.
Abstract: The major mechanisms of urea turnover and of active ion transport in osmoregula- tory organs are reviewed. Using published values for the molecular flow through these systems it is possible to estimate the energetic cost of osmotic regulation in hyporegulating marine teleosts and in ureotelic elasmobranchs. Oxygen consumption dedicated to osmotic regulation in the flounder (Platichthys flesus) is about 7 ml kg−1 hr−1 and in the rainbow trout (Salmo gairdneri) 6 ml kg−1 hr−1 For a dogfish (Scyliorhynus canicular) it was 5 ml kg−1 hr−1 and for the skate (Raja erinacea) 5 or 11 ml kg−1 hr−1 based on two values for urea loss by the fish. Both groups of fish used 10–15% of their standard metabolism for osmotic regulation. There are a number of uncertainties that may require modification of these values. It is not known whether TMAO lost by ureotelic regulators is replaced by ingestion or by synthesis. If by synthesis, the cost of regulation would be higher than calculated. Even more serious is the uncertainty regarding the use of organic osmolytes to maintain equilibrium between cells and blood. This strategy almost certainly requires some energy input, but there is insufficient information to permit its quantitative estimation, so the factor was omitted from the calculation. Among hyporegulators the sole unknown is whether the esophagus may absorb some of the ingested salt by diffusion. If so, it would decrease the energy expended in the intestinal tract and lower the total cost of regulation. The conclusion, based on known factors for the species examined, is that both modes are about equally efficient. If it becomes possible to factor in the unknowns it may be that hyporegulation is slightly more economical than ureosmotic. © 1993 Wiley-Liss, Inc.
TL;DR: The observed differences in stability between the four species suggest that isolation procedures should be modified according to the requirements for each species.
Abstract: Vitellogenin was purified from plasma of estradiol-17β-treated cod (Gadus morhua) rainbow trout (Oncorhynchus mykiss), turbot (Scophthalmus maximus), and wolffish (Anarhichas lupus) by precipitation with EDTA:Mg2+, distilled water, and high-performance ion-exchange chromatography. Vitellogenin of high purity was obtained by precipitation followed by chromatography, as evaluated by an homologous antiserum developed for each species. The instability of vitellogenin demanded consistent low temperature and the use of protease inhibitor before blood sampling. When the necessary precautions were taken, vitellogenin from rainbow trout, turbot, and wolffish eluted as one regular peak during chromatography. Cod vitellogenin eluted as two peaks and these demonstrated identical migration patterns on SDS-PAGE. The observed differences in stability between the four species suggest that isolation procedures should be modified according to the requirements for each species. Electrophoresis of plasma from treated fish revealed the presence of several smaller proteins, with a molecular mass around 50 kDa, that were considered to be vitelline envelope proteins. Other minor plasma proteins were immunoreactive to antisera, directed against vitellogenin and therefore judged to be fragments of degraded vitellogenin. © 1993 Wiley-Liss, Inc.
TL;DR: The leopard gecko, Eublepharis macularius, has temperature-dependent sex determination (TSD), and incubation at even higher temperatures (34 and 35 degrees C) produces mostly females (Pattern II).
Abstract: The leopard gecko, Eublepharis macularius, has temperature-dependent sex determination (TSD). Previous reports have shown that females are produced predominantly at cool incubation temperatures and males are produced predominantly at warm incubation temperatures (Pattern Ib). We report here that incubation at even higher temperatures (34 and 35 degrees C) produces mostly females (Pattern II). The lethal maximum constant incubation temperature for this species appears to be just above 35 degrees C. Although a previous study indicated that females from a warm incubation temperature (32 degrees C) failed to lay eggs, we found that 12 of 14 mature females incubated at 32.5 degrees C, and 5 of 6 mature females incubated at 34 degrees C produced fertile eggs and viable hatchlings.
TL;DR: The effects of handling and isolation caused a significant increase in both plasma cortisol and glucose levels, which remained relatively constant throughout the day-roosting period and significantly declined to their lowest level in the period following food presentation.
Abstract: Plasma levels of glucocorticoids and glucose were measured in three species of fruit bats (Chiroptera) sampled from captive populations. Three species of Old World bats (Pteropus vampyrus, P. Hypomelanus, and Rousettus aegyptiacus) had plasma levels of glucose that were within the normal mammalian range (80–100 mg/dl), with no difference between males and females. All animals had detectable levels of one or both of the major glucocorticoids (cortisol and corticosterone) found in mammals. Steroid levels were highest in P. hypomelanus (cortisol: 1,269 ± 207 ng/ml; corticosterone; 590 ± 154 ng/ml) and lowest in R. aegyptiacus (corticosterone: 36 ± 4 ng/ml; cortisol not determined). Diurnal changes in these steroids and the effects of handling and restraint stress were further investigated in P. hypomelanus. Experimental animals were captured in their roost quarters, bled once by venupuncture within 3 min, placed singly into a small holding chamber for 50–60 min, and bled again. This procedure was performed at four different times over the course of 24 h with different groups of animals. Glucose was at a minimum just before and a maximum just after the period of food presentation. Cortisol levels remained relatively constant throughout the day-roosting period and significantly declined to their lowest level in the period following food presentation. As expected, the effects of handling and isolation caused a significant increase in both plasma cortisol and glucose levels. When individual P. hypomelanus were subjected to 3 h restraint stress in small plastic wire-mesh restraining devices, cortisol levels rose approximately 800% by 2 h, with the first significant increase at 20 min. Thus, effects of sampling time (time of day) on plasma levels of cortisol and glucose should be considered when designing field and laboratory studies in which hormones and other blood borne parameters are being measured. Handling and bleeding times that exceeded 3 min were associated with elevated plasma levels of cortisol and glucose above resting (unstressed) levels, suggesting that field and laboratory protocols should be designed to reduce or eliminate this problem. Finally, the exceptionally high levels of plasma corticoids in P. hypomelanus, and to a lesser extent in P. vampyrus, place these bats among the highest known circulating adrenal steroid levels of all mammals. © 1993 Wiley-Liss, Inc.
TL;DR: Evidence is accruing that prolactin is involved in the adaptation to low magnesium diets, and endocrine factors determining the relative densities of calcium pumps in basolateral plasma membranes.
Abstract: The euryhaline tilapia Oreochromis mossambicus kept in fresh water takes up calcium mainly from the water via the gills, like other freshwater fish. In the gills specialized mitochondria-rich cells, the chloride cells, are thought to mediate a transcellular Ca2+ transport. Second messenger operated calcium channels (SMOCs) in the apical membrane, regulated by the hormone stanniocalcin, allow minute-to-minute control over the entry of Ca2+. In the basolateral plasma membranes of these cells, an ATP-consuming Ca2 + transporting enzyme provides the major driving force for extrusion of Ca2+ into the blood; in addition, an Na+ /Ca2+ exchanger is present in these membranes. The kinetics of the exchanger in vitro indicate that this extrusion mechanism dominates when intracellular calcium levels reach micromolar levels. In the gills, the transport of calcium appears primarily ATPase mediated and therefore largely independent of the Na+ status of the transporting cell. In enterocytes, similar mechanisms for transcellular transport of Ca2+ exist. However, in the intestinal epithelium the extrusion of Ca2+ is primarily via the Na+/Ca2+ exchanger and to a very limited extent mediated via the Ca2+-ATPase. Indeed, calcium transport over the intestinal epithelium is dependent on the Na+ -status and the Na+/K+-ATPase activity of the epithelium. Prolactin and cortisol are endocrine factors determining the relative densities of calcium pumps in basolateral plasma membranes.
At least 80% of the magnesium required for growth and homeostasis is absorbed from the food via the intestine. Magnesium is transported transcellularly and actively via enterocytes. The movement of Mg2+ over the apical membrane is passive, down an electrochemical gradient. The cytosolic Mg2+ concentration is kept well below its equilibrium concentration. The extrusion over the basolateral plasma membrane is mediated by an ATP-consuming enzyme. The gills contribute less than 20% to magnesium uptake, but up to 50% in tilapia fed a magnesium deficient diet. Evidence is accruing that prolactin is involved in the adaptation to low magnesium diets. © 1993 Wiley-Liss, Inc.
TL;DR: The restrictive definitions mentioned above for vivipar- ity and ovoviviparity are used in this discussion, since the "grey areas" of nutrient uptake found in placental reptiles, and in fishes, seem not to obtain in amphibians.
Abstract: Oviductal retention of developing embryos, with provision for maternal nutrition after yolk is exhausted (viviparity) and maintenance through metamorphosis, has evolved indepen- dently in each of the three living orders of amphibians, the Anura (frogs and toads), the Urodela (salamanders and newts), and the Gymnophiona (caecilians) In anurans and urodeles obligate vivi- parity is very rare (less than 1% of species); a few additional species retain the developing young, but nutrition is yolk-dependent (ovoviviparity) and, at least in salamanders, the young may be born be- fore metamorphosis is complete However, in caecilians probably the majority of the approximately 170 species are viviparous, and none are ovoviviparous All of the amphibians that retain their young oviductally practice internal fertilization; the mechanism is cloaca1 apposition in frogs, spermato- phore reception in salamanders, and intromission in caecilians Internal fertilization is a necessary but not sufficient exaptation (sensu Gould and Vrba: Paleobiology 8:4-15, '82) for viviparity The sala- manders and all but one of the frogs that are oviductal developers live at high altitudes and are subject to rigorous climatic variables; hence, it has been suggested that cold might be a "selection pressure" for the evolution of egg retention However, one frog and all the live-bearing caecilians are tropical low to middle elevation inhabitants, so factors other than cold are implicated in the evolu- tion of live-bearing Viviparity might facilitate life in a rigorous environment, but likely is not "caused by such an existence o 1993 Wiley-Liss, Inc Oviductal retention of developing embryos has evolved independently several times in members of the Class Amphibia-twice in Anura (frogs and toads), once in Urodela (salamanders and newts), and at least twice, perhaps three times, in Gymno- phiona (caecilians) Each group has effected retention in rather different ways, and none have developed placentas (with the possible exception of a pseudo- placenta in one group of caecilians) In all species of amphibian oviductal embryo retainers for which there are data, either little to no nutrition is sup- plied in addition to yolk, though there may be gas- eous exchange across vascularized membranes (ovoviviparity), or cells of the oviductal epithelium secrete a highly nutritious material that is orally ingested by the developing fetuses after yolk is re- sorbed (viviparity) (Amoroso, '52, '68) Amphibians may present a special case in that viviparity and ovoviviparity can be rather clearly delineated in terms of presence or absence of significant mater- nal nutrition (a protein, carbohydrate and lipid-rich material, depending on the stage of development) following yolk resorption I therefore will use the restrictive definitions mentioned above for vivipar- ity and ovoviviparity in this discussion, since the "grey areas" of nutrient uptake found in placental reptiles, and in fishes, seem not to obtain in amphibians Of nearly
TL;DR: In spite of some common features, both structural and functional differences remain and it is suggested that use of terms such as mononuclear giant cells, multinucleate Giant cells, and binucleate cells be continued rather than assuming that these cells are all members of a single trophoblastic subtype.
Abstract: The cellular origin, structure, and function of trophoblastic giant cells (GC) and binucleate cells (BNC) are reviewed. Mammals in which these cells have received the greatest attention include rodents, rabbits, and humans (GCs), and ruminants and equids (BNCs). In almost all cases these cells arise from the cytotrophoblast. All are large cells and contain either two diploid nuclei (BNCs), multiple nuclei (human placental bed GCs), or single nuclei with amplified DNA content (rodent and rabbit GCs). Giant and binucleate cells typically exhibit the capacity for migration or invasion, although the degree of migratory activity varies between species. While most end up within, or at the interface with, endometrial tissue, in some instances the GCs or BNCs contribute directly to the interhemal membrane of the placenta. Hormone production is a property which most GC-BNC populations have in common. Lactogen or gonadotropin has been documented in almost all cells of this type examined to date, and in some animals they are also steroidogenic (e.g., rats and sheep). In spite of some common features, both structural and functional differences remain and it is suggested that use of terms such as mononuclear giant cells, multinucleate giant cells, and binucleate cells be continued rather than assuming that these cells are all members of a single trophoblastic subtype.
TL;DR: The results are consistent with the proposition that the TE acts as a transporting epithelium, sparing nutrients for metabolism by the ICM, and the uptake of glucose and pyruvate was low in both cell types.
Abstract: The two cell populations of the day 5 mouse blastocyst–the inner cell mass (ICM) and trophectoderm (TE)–were isolated by immunosurgery and TE biopsy. The uptake of glucose and pyruvate and the production of lactate were measured in the isolated cell populations and in single day 5 blastocysts, using a non-invasive ultramicrofluorescence technique. The number of cells in isolated ICMs, TE vesicles, and intact blastocysts were counted after differential labeling with fluorochromes. The uptake of glucose and the formation of lactate were approximately three and five times greater, respectively, in the ICM cells compared with the TE cells. All the glucose consumed by the ICM could be accounted for by lactate formation, whereas the value for TE was 55%. The uptake of pyruvate was low in both cell types. The results are consistent with the proposition that the TE acts as a transporting epithelium, sparing nutrients for metabolism by the ICM. © 1993 Wiley-Liss, Inc.
TL;DR: The yolk sac of viviparous reptiles contributes to three categories of placentation, the choriovitelline placenta, which also occurs in marsupial and eutherian mammals, and the Omphaloplacenta and omphalallantoic placentA, which occur only among squamate reptiles (lizards and snakes).
Abstract: The extraembryonic membranes of amniote vertebrates are shared structures that have a brief, yet substantive role in the ontogeny of the organism. The yolk sac, which is the first of these structures to develop, has an important function in regulation and mobilization of nourishment to embryos of oviparous species and additionally contributes to maternal-fetal exchange in many viviparous species. Yolk sac placentation has been described in all major taxa of viviparous amniotes. The yolk sac of viviparous reptiles contributes to three categories of placentation, the choriovitelline placenta, which also occurs in marsupial and eutherian mammals, and the omphaloplacenta and omphalallantoic placenta, which occur only among squamate reptiles (lizards and snakes). The fetal contribution to the omphaloplacenta includes a structure termed the isolated yolk mass, which forms in all Squamata independent of reproductive mode, and is produced by a morphogenesis of extraembryonic mesoderm that is unique to this reptilian order. For some viviparous squamates, the allantois contributes to the inner margin of the isolated yolk mass and this structural arrangement constitutes the omphalallantoic placenta. The isolated yolk mass is bordered externally by a bilaminar omphalopleure. Epithelial cells of the bilaminar omphalopleure of the omphaloplacenta and omphalallantoic placenta are hypertrophied. The apposed uterine epithelium likewise contains enlarged cuboidal or columnar shaped cells and the underlying lamina propria is richly vascularized. This epithelial cell structure suggests that the region of the isolated yolk mass is a site of placental specialization in viviparous reptiles. Further, since these features of omphaloplacentation or omphalallantoic placentation commonly occur in species without apparent morphological specialization in other areas of fetal-uterine contact, it is likely that the bilaminar omphalopleure of the isolated yolk mass is evolutionarily the initial site of placental specialization among viviparous reptiles. © 1993 Wiley-Liss, Inc.
TL;DR: It is shown that thapsigargin, a highly specific inhibitor of the endoplasmic reticulum Ca(2+)-ATPase Ca( 2+)-pump (and thus a mobilizer of intracellular Ca2+) in other cells, can initiate the AR in capacitated human sperm.
Abstract: Previous studies have established that the mammalian sperm acrosome reaction (AR) is dependent upon an influx of extracellular Ca2+, but the involvement of a mobilizable store of intracellular Ca2+ has not been shown. In many other cells, the endoplasmic reticulum is the site of such a Ca2+ -store. Here, we show that thapsigargin, a highly specific inhibitor of the endoplasmic reticulum Ca2+ -ATPase Ca2+ -pump (and thus a mobilizer of intracellular Ca2+) in other cells, can initiate the AR in capacitated human sperm. Thapsigargin at concentrations from 50–500 nM significantly increased the AR to the same extent when incubated with capacitated sperm for 1 min (assayed by indirect immunofluorescence). Transmission electron microscopy confirmed the occurrence of normal morphologyin the AR initiated by thapsigargin. Thapsigargin (200 nM) did not initiate the AR in noncapacitated sperm. Inititation of the AR by thapsigargin apparently requires an influx of Ca2+ since 1 min preincubation with the calcium channel blockers La3+ (250 μM) or Ni2+ (250 μM) prior to addition of thapsigargin completely inhibits AR-initiation. Mobilization of an intracellular Ca2+ -store by thapsigargin in capacitated human sperm may lead to an influx of extracellular Ca2+ and subsequently the AR. Putative sites for thapsigargin-sensitive intracellular Ca2+ -stores in human sperm include the cytoplasmic droplet, the sperm nucleus and the acrosome. © 1993 Wiley-Liss, Inc.
TL;DR: It is argued that the successful placental arrangements are those that decrease the exposure of the trophoblast to the efferent side of the cellular immune response.
Abstract: It is argued that the successful placental arrangements are those that decrease the exposure of the trophoblast to the efferent side of the cellular immune response. Examples are taken from three different groups with hemochorial placentation, to show that their placental morphology places most of the trophoblast in contact with maternal blood, not maternal connective tissue. In addition, maternal cells of the junctional area are modified either before contact with trophoblast (rat) or just after trophoblast invasion (primate), or the region of contact is limited as in the armadillo, in which maternal blood sinuses are expanded to form intervillous spaces.
TL;DR: The intracellular concentration of organic osmolytes in isolated mammalian kidney cells responds dramatically to changes in the osmotic environment, and the release of sorbitol following hypoosmotic exposure appears to be triggered by calcium, possibly via a mechanism involving membrane recycling.
Abstract: Cells of marine species are known to establish osmotic balance with their environment by adjusting the concentrations of organic osmolytes rather than inorganic osmolytes such as sodium, potassium, and chloride. These organic osmolytes fall into three classes: polyhydric alcohols such as sorbitol, amino acids and amino acid derivatives, and urea and trimethylamines. Substantial evidence is available for a central role of each of these classes in osmoregulation in marine species. In this chapter information on the importance of organic osmolytes is extended to a study of isolated mammalian kidney cells. The intracellular concentration of organic osmolytes in these cells responds dramatically to changes in the osmotic environment. The release of sorbitol following hypoosmotic exposure appears to be triggered by calcium, possibly via a mechanism involving membrane recycling. The summarized experiments provide a basis for further work in marine species. © 1993 Wiley-Liss, Inc.
TL;DR: Among the carnivores, development of the fetal membranes and placentation have now been particularly well studied in the domestic cat, and the efficiency of maternal- Fetal physiological exchange depends not only upon the thickness of the interhemal membrane, but also upon the materno-fetal blood flow interrelationship.
Abstract: Among the carnivores, development of the fetal membranes and placentation have now been particularly well studied in the domestic cat (Felis catus). Initially, the cat conceptus is bordered by a primitive and a precontact chorion. This becomes part of a temporary choriovitelline placenta which is subsequently supplanted by a chorioallantoic placenta. Following thiphasic process of implantation (which involves apposition, adhesion, and intrusion), the chorioallantoic placenta forms a zonary girdle which separates two paraplacental cupules. These cupules are subdivided from base to tips into 1) extravasate zones with hematomal areas and solid junctional areas containing intermingled fetal and maternal tissue, 2) free polar zones with almost no feto-maternal contact, and 3) interplacental polar zones freely projecting into the uterine lumen or, near the end of pregnancy, facing comparable regions of neighboring fetuses.
The placental girdle consists of a lamellar zone characterized by elongate, parallel fetal (chorionic) and maternal (septal) lamellae, a junctional zone where fetal and maternal tissues face each other and intimately intermingle, and a zone of pure endometrial glands. In the lamellar zone the interhemal membrane (placental barrier) is of the endotheliochorial type. As pregnancy progresses, cytotrophoblast in the interhemal barrier contributes to the formation of syncytiotrophoblast and is gradually reduced from being a continuous layer to only scattered cells. The syncytiotrophoblast is usually separated from endothelial cells of the maternal capillaries by a thickened basal lamina (the interstitial membrane) or faces persisting endometrial connective tissue containing some enlarged decidual cells.
The efficiency of maternal-fetal physiological exchange depends not only upon the thickness of the interhemal membrane, which in reduced in places to 1.5 μm, but also upon the materno-fetal blood flow interrelationship. This is of the simple crosscurrent type in the cat. © 1993 Wiley-Liss, Inc.
TL;DR: It is demonstrated that EGF, in the absence of pFF, promotes a similar level of oocyte nuclear maturation as does pFF alone or pFF with EGF and/or IGF-I.
Abstract: Undefined follicular factors that may influence nuclear maturation and/or cytoplasmic maturation are required during in vitro maturation of pig oocytes. Epidermal growth factor (EGF), insulin-like growth factor-I (IGF-I), and dialysed porcine follicular fluid (dpFF) were evaluated for their effects on porcine oocyte nuclear maturation in vitro. In Experiment I, eight different maturation media were made in a split-plot factorial design with dpFF (0% vs. 10% v/v dialyzed pFF) as the whole plot component, and EGF (0.0 vs. 50 ng/ml) and/or IGF-I (0.0 vs. 100 ng/ml) as the factorial subplot component. Experiment II was a complete factorial design with dpFF and EGF. Pig follicular granulosa-cumulus-oocyte complexes (GCOC) were obtained from slaughterhouse ovaries, washed, and cultured at 38.5°C in a humidified incubator with 5% CO2 in air for 42 h. Following culture, GCOC were mechanically stripped of granulosa-cumulus cells and evaluated for nuclear maturation by light microscopy. In Experiment I, the percentage of Metaphase II oocytes for control, IGF-I, EGF, and IGF-I + EGF treatments without pFF were 50.7%, 52.6%, 80.9%, and 84.3% (control and IGF-I groups significantly less, P<.001). The same treatments in the presence of pFF were similar and high (84.2, 84.9, 82.1, and 86.8%, respectively). Experiment II gave similar results. These results demonstrate that EGF, in the absence of pFF, promotes a similar level of oocyte nuclear maturation as does pFF alone or pFF with EGF and/or IGF-I. IGF-I does not appear to influence nuclear maturation of GCOC. © 1993 Wiley-Liss, Inc.
TL;DR: It is suggested that the cumulus oophorus sequesters and brings to the immediate vicinity of the eggs the few spermatozoa which gain the ampulla at or soon after ovulation, so favoring early fertilization.
Abstract: The cumulus oophorus, unique to the egg of eutherian mammals, has been suggested to function either in egg transport to the oviduct ampulla, in avoidance of polyspermy, in enhancement of sperm fertilizing ability, or in sperm guidance to the egg. To examine its role further, the content of the oviduct ampulla was collected at 0700–0730 h, 1130–1200h, or 1600–1700 h on the day of ovulation from rats mated once or more than once, and analysed with an emphasis on sperm distribution in the ampullary fluid, in the cumulus, and in the eggs. The distribution of spermatozoa between cumulus and ampullary fluid was highly skewed (ca. 9:1) at all times in favor of the cumulus. In 14.1% of the ampullae collected by 0730 h the only spermatozoa present were those already within eggs; and in many other ampullae then there were no more than one or so additional spermatozoa outside fertilized eggs—a testament to the efficiency of the mechanisms that ensure an early meeting of gametes in the oviduct. There was a gradual increase in the total number of spermatozoa in the ampulla throughout the day of ovulation, and the time of eventual cumulus dispersal later in the day generally reflected the number of spermatozoa within it, rather than the occurrence of fertilization per se.
These observations suggest that the cumulus oophorus sequesters and brings to the immediate vicinity of the eggs the few spermatozoa which gain the ampulla at or soon after ovulation, so favoring early fertilization. The sperm/cumulus relationship, sperm/egg communication, and the situation in viviparous vertebrates whose eggs are cumulus-free are discussed briefly. © 1993 Wiley-Liss, Inc.
TL;DR: Survival was directly related to the rate of evaporative water loss, with the highest level of survival being afforded by the most gradual dehydration regime, and the existence of a transition phase in the dehydration process, where nematodes required further dehydration before revival could occur.
Abstract: The effects of differential rates of evaporative water loss on the survival capabilities of small aggregates (ca. 10 mg wet wt) of Aphelenchus avenae were assessed. This was achieved using a comparative approach between rapid (direct transfer of preconditioned nematodes to successively compounds accumulated were also assessed during the induction process. Glyecrol and glucos levels remained low (< 1% dry wt)) while trehalose levels increased dramatically during preconditioning (8–10% dry wt), but the elevated levels were unable to support survival during periods of rapid water loss. Survival was directly related to the rate of evaporative water loss, with the highest level of survival being afforded by the most gradual dehydration regime. In addition, the water loss curves identified a critical period where hydration levels ranged from 40% to 12% H2O. During this time, slow drying was essential if the nematodes were to successfully survive the dehydration process. Survival curves also revealed the existence of a transition phase in the dehydration process, where nematodes required further dehydration before revival could occur. These results are discussed in relation to the adaptive significance of polyhydroxy compound accumulation and the probable role that specific hydration levels play in the implementation of other adaptations at the cellular and subcellular levels. © 1993 Wiley-Liss, Inc.
TL;DR: The results, particularly those from delayed and reactivated blastocysts, show that genome endoreduplication is not an obligatory early event in the transformation of mural trophectoderm cells.
Abstract: Prominent among the various types of cell that differentiate from the trophectoderm of the mouse blastocyst are trophoblastic giant cells. Repeated endoreduplication of the genome accompanies the growth of these cells, which have been shown to be polytene rather than polyploid. Early stages in giant transformation have been examined, mainly in the mural trophectoderm of the implanting blastocyst which gives rise to the primary trophoblastic giant cells. One confusing issue is whether these early stages include the onset of endoreduplication of the genome. This issue has been addressed in the present study by comparing the DNA content of nuclei in isolated trophectoderm and ICM tissue rather than, as previously, by relating measurements on air-dry preparations of entire blastocysts to those of adult liver. The results, particularly those from delayed and reactivated blastocysts, show that genome endoreduplication is not an obligatory early event in the transformation of mural trophectoderm cells.
TL;DR: The feasibility of using a laser microbeam to induce a sub-lethal heat shock response in individual cells of Caenorhabditis elegans is investigated and it is demonstrated that in transgenic strains carrying heat shock promoter-lacZ fusions, single cell expression of beta-galactosidase in a variety of cell types of endodermal, mesoder mal, or ectodermal origin can be achieved after pulsing with a laser.
Abstract: Heat shock promoters have been employed to achieve tightly regulated expression of transformed genes in a wide variety of model systems including tissue culture cells, bacteria, yeast, Drosophila, and more recently Caenorhabditis elegans. Here we investigate the feasibility of using a laser microbeam to induce a sub-lethal heat shock response in individual cells of C. elegans. We demonstrate that in transgenic strains carrying heat shock promoter-lacZ fusions, single cell expression of β-galactosidase in a variety of cell types of endodermal, mesodermal, or ectodermal origin can be achieved after pulsing with a laser. A tissue-general, inducible promoter can therefore be converted into one of single cell specificity which can be induced rapidly at any point in development, offering unique opportunities to study cell-cell interactions in C. elegans. This technique defines a new approach to generate mosaic animals and may be adaptable to other organisms or tissues. © 1993 Wiley-Liss, Inc.
TL;DR: This YSL transition sets the stage for the onset of gastrulation and is preceded by increased duration and variability of succeeding mitoses and, in particular, duration of their interphases, a decrease and deceleration in the rate of the last metachronous waves, and, finally, by the complete cessation of mitosis and the entry of YSL nuclei into permanent interphase.
Abstract: Because of its importance in early embryogenesis, the developmental history of the yolk syncytial layer (YSL) of Fundulus has been investigated in detail. As in other teleosts, the Fundulus YSL forms mainly by collapse of certain marginal blastomeres which then merge with the cytoplasm of the yolk cell peripheral to the blastoderm. Nuclei enter the yolk cell from these open blastomeres variably during cleavages 8–11, but most frequently at cleavages 9 and 10. After entry, the first nuclei divide five times and later nuclei divide with them. Thus, nuclei that have invaded at the next cleavage divide four times, etc. When the first YSL nuclei cease dividing, all other YSL nuclei cease dividing with them. These YSL mitoses occur in metachrony. Two or more metachronous waves progress through the YSL cytoplasm at each mitosis. After each nuclear division, the YSL increases in width and its nuclei are quite evenly spaced. After the 5th and last mitosis, when the YSL is at its widest, it contracts in its animal-vegetal axis. This slow contraction has two major effects: 1) narrowing of the YSL, accompanied by crowding of its nuclei and their disappearance beneath the blastoderm to nucleate the internal YSL; 2) epibolic expansion of the I-YSL and the blastoderm, followed soon after by other cell movements of gastrulation. This YSL transition, therefore, sets the stage for the onset of gastrulation. It is preceded by increased duration and variability of succeeding mitoses and, in particular, duration of their interphases, a decrease and deceleration in the rate of the last metachronous waves, and, finally, by the complete cessation of mitosis and the entry of YSL nuclei into permanent interphase. © 1993 Wiley-Liss, Inc.