Showing papers in "Cellular and Molecular Life Sciences in 1990"
TL;DR: The present article considers the basic mechanisms and principles of neuronal cell migration in the mammalian central nervous system and considers surface-mediated interaction between neighboring cells.
Abstract: A basic property of immature neurons is their ability to change position from the place of their final mitotic division in proliferative centers of the developing brain to the specific positions they will occupy in a given structure of the adult nervous system. Proper acquisition of neuron position, attained through the process of active migration, ultimately affects a cell's morphology, synaptic connectivity and function. Although various classes of neurons may use different molecular cues to guide their migration to distant structures, a surface-mediated interaction between neighboring cells is considered essential for all types of migration. Disturbance of this cell-cell interaction may be important in several congenital and/or acquired brain abnormalities. The present article considers the basic mechanisms and principles of neuronal cell migration in the mammalian central nervous system.
619 citations
TL;DR: Many aspects of metal-microbe interactions remain unexploited in biotechnology and further development and application is necessary, particularly to the problem of radionuclide release into the environment.
Abstract: Bacteria, and other microorganisms, exhibit a number of metabolism-dependent and-independent processes or the uptake and accumulation of heavy metals and radionuclides. The removal of such harmful substances from effluents and waste waters by microbe-based technologies may provide an alternative or additional means of metal/radionuclide recovery for economic reasons and/or environmental protection. Both living and dead cells as well as products derived from or produced by microorganisms can be effective metal accumulators and there is evidence that some biomass-based clean-up processes are economically viable. However, many aspects of metal-microbe interactions remain unexploited in biotechnology and further development and application is necessary, particularly to the problem of radionuclide release into the environment.
468 citations
TL;DR: It is suggested that these compounds may play a wide-ranging role in the territorial marking behavior of male mice, and may be synonymous with the previously described aversion signal produced by dominant males.
Abstract: Two terpenic constituents, E,E,-alpha-farnesene and E-beta-farnesene, were found to be elevated in dominant male urine when compared to subordinate or control males. These two urinary compounds were absent in the bladder urine of males; however, they were the most prominent constituents of the perputial gland's aliquots. The results of a two-choice preference test, conducted on ICR/Alb subordinate males, gave a strong indication that these two terpenic constituents introduced into the previously attractive stimulus significantly discouraged prolonged investigations by male mice. The compounds, whether present in the urine matrix or water, rendered the stimulus with a quality behaviorally similar to the urine of dominant males. It appears that they may be synonymous with the previously described aversion signal produced by dominant males. We suggest that these compounds may play a wide-ranging role in the territorial marking behavior of male mice.
213 citations
TL;DR: In vivo analyses of developing cerebellum demonstrate a close coordination of afferent axon ingrowth relative to target cell migration, and studies indicate that climbing fibers contact immature Purkinje neurons during the migration and settling ofPurkinje cells, implicating a role for afferents in the termination of migration.
Abstract: Our laboratory has developed an in vitro model system in which glial-guided neuronal migration can be observed in real time. Cerebellar granule neurons migrate on astroglial fibers by apposing their cell soma against the glial arm, forming a specialized migration junction, and extending a motile leading process in the direction of migration. In vitro assays indicate that the neuronal antigen astrotactin functions as a neuron-glia ligand, and is likely to play a role in the movement of neurons along glial fibers. In heterotypic recombinations of neurons and glia from mouse cerebellum and rat hippocampus, neurons migrate on heterotypic glial processes with a cytology, speed and mode of movement identical to that of neuronal migration on homotypic glial fibers, suggesting that glial fibers provide a permissive pathway for neuronal migration in developing brain. In vivo analyses of developing cerebellum demonstrate a close coordination of afferent axon ingrowth relative to target cell migration. These studies indicate that climbing fibers contact immature Purkinje neurons during the migration and settling of Purkinje cells, implicating a role for afferents in the termination of migration.
192 citations
TL;DR: A considerable body of indirect evidence is provided supporting a broad role for the FABP in the intracellular transport and metabolism of long-chain fatty acids and the existence of structure- and tissue-specific specialization of function among different members of the F ABP gene family.
Abstract: Cytosolic fatty acid binding proteins (FABP) belong to a gene family of which eight members have been conclusively identified. These 14–15 kDa proteins are abundantly expressed in a highly tissue-specific manner. Although the functions of the cytosolic FABP are not clearly established, they appear to enhance the transfer of long-chain fatty acids between artificial and native lipid membranes, and also to have a stimulatory effect on a number of enzymes of fatty acid metabolism in vitro. These findings, as well as the tissue expression, ligand binding properties, ontogeny and regulation of these proteins provide a considerable body of indirect evidence supporting a broad role for the FABP in the intracellular transport and metabolism of long-chain fatty acids. The available data also support the existence of structure- and tissue-specific specialization of function among different members of the FABP gene family. Moreover, FABP may also have a possible role in the modulation of cell growth and proliferation, possibly by virtue of their affinity for ligands such as prostaglandins, leukotrienes and fatty acids, which are known to influence cell growth activity. FABP structurally unrelated to the cytosolic gene family have also been identified in the plasma membranes of several tissues (FABPpm). These proteins have not been fully characterized to date, but strong evidence suggests that they function in the transport of long-chain fatty acids across the plasma membrane.
167 citations
TL;DR: Theδ-endotoxin fromBacillus thuringiensis subspecieskurstaki strain HD1-9 is almost 400 times more potent than the δ- endotoxins from strain HD-73 as a gypsy moth larvicide.
Abstract: The delta-endotoxin from Bacillus thuringiensis subspecies kurstaki strain HD1-9 is almost 400 times more potent than the delta-endotoxin from strain HD-73 as a gypsy moth larvicide. The two delta-endotoxins compete for a high-affinity binding site on the brush border membrane of larval gypsy moth midguts. The affinity for the delta-endotoxin from strain HD-73 is much greater than the affinity for the delta-endotoxin from strain HD1-9.
163 citations
TL;DR: The main emphasis has been placed on the occurrence, general purification procedures, macromolecular properties, sugar specificities and applications of these lectins.
Abstract: The literature contains several reviews on lectins in general, covering mainly those from plants and invertebrates. However, the sialic acid binding lectins have not been reviewed so far. Considering the importance of sialic acids in cell sociology, lectins which specifically recognize terminal sialic acid residues are potentially useful as analytical tools in studying the biological functions of sialoglycoconjugates. These lectins, along with monoclonal antibodies raised against sialoglycoconjugates, have been used in the detection, affinity purification, cytochemical localization and quantitation of such glycoconjugates. In this review the main emphasis has been placed on the occurrence, general purification procedures, macromolecular properties, sugar specificities and applications of these lectins.
135 citations
TL;DR: To test whether mole-ratsCryptomys hottentotus were able to use the magnetic field for orientation, laboratory experiments were conducted which were based on the animals' spontaneous tendency to build their nests at the same position in a circular arena, showing that they can use the Magnetic field for direction finding.
Abstract: To test whether mole-ratsCryptomys hottentotus were able to use the magnetic field for orientation, laboratory experiments were conducted which were based on the animals' spontaneous tendency to build their nests at the same position in a circular arena. In the local geomagnetic field, the animals preferred the SE-sector. When magnetic north was turned by 120o or by 180o, the mole-rats changed their nest position accordingly. This clearly shows that they can use the magnetic field for direction finding.
124 citations
TL;DR: Data indicate that the dehydroecdysone-ECDysone axis is not restricted to moths and butterflies, and activity was demonstrated in members of other orders.
Abstract: The prothoracic glands of a variety of insects were tested for their ability to synthesize ecdysteroids in vitro. More specifically, they were evaluated for their ability to produce 3-dehydroecdysone and ecdysone using both radioimmunoassay and reverse phase high performance liquid chromatography. Three categories of insect prothoracic glands were noted: a) those producing much more 3-dehydroecdysone than ecdysone; b) glands synthesizing almost equivalent amounts of each of these two ecdysteroids; c) prothoracic glands that yielded more ecdysone than 3-dehydroecdysone. In addition, the 3-oxoecdysteroid 3β-reductase activity of the hemolymph of these insects was evaluated for its ability to convert 3-dehydroecdysone to ecdysone. The lepidopteran species tested yielded the most potent enzyme activity, although activity was demonstrated in members of other orders. These data indicate that the dehydroecdysone-ecdysone axis is not restricted to moths and butterflies.
118 citations
TL;DR: In this paper, a review of microbial transformations of typical waste components such as metal oxides, metal coprecipitates, naturally occurring minerals, and metal organic complexes are reviewed.
Abstract: Microbial activity in mixed wastes can have an appreciable effect on the dissolution or precipitation of toxic metals and radionuclides. Fundamental information on microbial dissolution and stabilization (immobilization) of toxic metals and radionuclides, in particular actinides and fission products, in nuclear wastes under various microbial process conditions, e.g., aerobic, denitrifying, iron-reducing, fermentative, sulfate-reducing, and methanogenic conditions is very limited. Microbial transformations of typical waste components such as metal oxides, metal coprecipitates, naturally occurring minerals, and metal organic complexes are reviewed. Such information can be useful in the development of 1) predictive models on the fate and long-term transport of toxic metals and radionuclides from waste disposal sites, and 2) biotechnological applications of waste treatment leading to volume reduction and stabilization as wall as recovery and recycling of radionuclides and toxic metals.
115 citations
TL;DR: The mathematical theory of renormalization groups provides a description of the harmonically-modulated inverse power-law scaling observed for bronchial tree dimensions observed in different species.
Abstract: The mammalian lung exhibits features of a fractal tree: heterogeneity, self-similarity and the absence of a characteristic scale. The finite nature of the lung ultimately limits the range over which self-similarity scaling characteristics are applicable. However, generalization based on the scaling features of fractals, provides unique insight into geometric organization of anatomic structures. Furthermore, the mathematical theory of renormalization groups provides a description of the harmonically-modulated inverse power-law scaling observed for bronchial tree dimensions observed in different species. Compared to several mammalian species (dog, rat, hamster), the human lung shows marked differences in the phase of the harmonic modulation for both length and diameter measurements. These inter-species scaling differences suggest that evolutionary factors modify certain universal features of morphogenesis.
TL;DR: It is reported that organismal performance traits had the highest heritabilities in a natural population of garter snakes.
Abstract: Locomotor capacities and their physiological bases are thought to be of considerable selective importance in natural populations. Within this functional complex, organismal performance traits (e.g., speed, stamina) are expected to be of more direct selective importance than their suborganismal determinants (e.g., heart size). Quantitative genetics theory predicts that traits of greater selective importance should generally have lower heritabilities at equilibrium. Contrary to these expectations, we report that organismal performance traits had the highest heritabilities in a natural population of garter snakes.
TL;DR: In this paper, the authors suggest that the general basis of migratory orientation in birds is most probably an endogenous time-and-direction program, where directions are selected with respect to celestial and geomagnetic clues.
Abstract: The general basis of migratory orientation in birds is most probably an endogenous time-and-direction program. Directions are selected with respect to celestial and geomagnetic clues. Using these clues, a bird may reach a large population-specific area; however, it will hardly be able to find a particular location, for instance its previous breeding site. Homing to a familiar site over several hundred kilometres of unfamiliar terrain appears to be based on the smelling of atmospheric trace compounds. Conceptual approaches to the mechanism of olfactory navigation have as yet only reached an early state of speculation.
TL;DR: The following possible causes are regarded as contributing to changes in the non-plant mt: directional mutation pressure, genomic economization, changes in charging specificity of tRNAs, loss of release factor RF2, changesIn RF1,Changes in anticodons, loss in lysidine-forming enzyme system, and disappearance of codons from coding sequences.
Abstract: The universal genetic code is used without changes in chloroplasts and in mitochondria of green plants. Non-plant mitochondria use codes that include changes from the universal code. Chloroplasts use 31 anticodons in translating the code; a number smaller than that used by bacteria, because chloroplasts have eliminated 10 CNN anticodons that are found in bacteria. Green plant mitochondria (mt) obtain some tRNAs from the cytosol, and genes for some other tRNAs have been acquired from chloroplast DNA. The code in non-plant mt differs from the universal code in the following usages found in various organisms: UGA for Trp, AUA for Met, AGR for Ser and stop, AAA for Asn, CUN for Thr, and possibly UAA for Tyr. CGN codons are not used byTorulopsis yeast mt. Non-plant mt, e.g. in vertebrates, may use a minimum of 22 anticodons for complete translation of mRNA sequences. The following possible causes are regarded as contributing to changes in the non-plant mt: directional mutation pressure, genomic economization, changes in charging specificity of tRNAs, loss of release factor RF2, changes in RF1, changes in anticodons, loss of lysidine-forming enzyme system, and disappearance of codons from coding sequences.
TL;DR: Some birds have unexplained abilities to sense the wind while aloft, and some birds recognize the need to change course to allow for previous wind displacement, and reorient at least roughly toward the original route or destination.
Abstract: Migratory flights are strongly affected by wind, and birds have developed many adaptations to cope with wind effects. By day, overland migrants at high altitudes may often allow crosswinds to drift their tracks laterally from the preferred heading. In contrast, many birds at low altitude adjust their headings to compensate for drift, and may overcompensate to allow for previous drift. The relative motion of landscape features is probably used to sense drift, at least by day. By night, some overland migrants compensate fully for drift but others do not; no pattern is obvious. Over the sea, compensation is rarely if ever total; wave patterns may allow partial compensation. Other adaptations can include reduction of drift by flying at times and/or altitudes without strong crosswinds. Some birds recognize the need to change course to allow for previous wind displacement, and reorient at least roughly toward the original route or destination. Some juveniles en route to previously-unvisited wintering grounds seem to have this ability, but corroboration is needed. Such reorientation may not require a true navigation ability. However, some birds have unexplained abilities to sense the wind while aloft.
TL;DR: It is shown that pigeons derive directional information from atmospheric odouts, and the lack of any knowledge about the chemical nature and distribution of the odorants which allow pigeons to navigate hinders progress.
Abstract: Many bird species rely on an osmotactic mechanism to find food sources even at a considerable distance. Pigeons also rely on local odours for homeward orientation, and they integrate those perceived during passive transportation with those at the release site. It is possible to design experiments in which birds are given false olfactory information, and predictions about the effects of this can be made and tested. Pigeons build up their olfactory map by associating wind-borne odours with the directions from which they come; this was shown by experiments which aimed at preventing, limiting or altering this association. Some objections have been made to this conclusion; namely that even anosmic pigeons are sometimes homeward oriented, that they may be demotivated in flying or disturbed in their general behaviour, and that olfactory cues may be only one component of pigeo's navigational repertoire. The most recent experiments, however, confirm that pigeons derive directional information from atmospheric odouts. The lack of any knowledge about the chemical nature and distribution of the odorants which allow pigeons to navigate hinders progress in this area of research.
TL;DR: The majority of extracellular complexing ligands produced by microorganisms are summarized as being of low molecular mass (<10,000 daltons) and are usually released as part of metal detoxification processes as discussed by the authors.
Abstract: The majority of extracellular complexing ligands produced by microorganisms are summarized as being of low molecular mass (<10,000 daltons) and are usually released as part of metal detoxification processes. These exudates appear to exhibit strong metal-binding characteristics, often reducing metal toxicity. Under certain conditions microbes produce metal-specific compounds of low molecular mass called siderophores; although these are normally specific for iron they also have relatively high affinities for radionuclides such as Pu and facilitate their uptake into cells. The occurrence of specific actinide complexing agents has been recorded. The breakdown of lignins and cellulosic material produces large macromolecular compounds called humates. These contain multiligand sites and display a wide range of complexing abilities. They form both soluble and insoluble complexes with toxic elements with various results. Humates also considerably influence adsorption of metals to substrate surfaces and at high pH may compete with OH-ions for metal binding. As well as with extracellular ligands, metals can interact directly with microorganisms by accumulation in subcellular compartments or by adsorption on bacterial surfaces.
Journal Article•
TL;DR: The scope of this review is to describe some of the more recent findings concerning the structure and mode of action of pore-forming colicins with a special attention to models of membrane insertion and pore structure based on the recently determined three-dimensional structure of the pore -forming domain of colicin A.
Abstract: Colicins are plasmid-encoded protein antibiotics which kill bacteria closely related to the producing strain (generally Escherichia coli). The study of the function of colicins has revealed many features which reflect common targeting and translocation mechanisms with bacteriophages and toxins. Like many toxins, colicins are composed of structural domains specialized in one of the different steps of the activity, targeting, translocation and killing. The major group comprises those colicins which permeabilize the cytoplasmic membrane, thereby destroying the cell's membrane potential. These colicins form well-defined voltage-gated ion channels in artificial membranes. The scope of this review is to describe some of the more recent findings concerning the structure and mode of action of pore-forming colicins with a special attention to models of membrane insertion and pore structure based on the recently determined three-dimensional structure of the pore-forming domain of colicin A.
TL;DR: The present results show that ACTH responses induced by intravenous injection of IL-1α were suppressed by systemic pretreatment with indomethacin and that intrahypothalamic injection of PGE2 stimulates the secretion of ACTH, suggesting that the ACTH response induced by IL- 1 is mediated by CRF secretion stimulated by hypothalamic P GE2.
Abstract: We investigated whether hypothalamic prostaglandin E2 (PGE2) and corticotropin releasing factor (CRF) are responsible for the development of the adrenocorticotropic hormone (ACTH) response induced by interleukin-1α (IL-1α). The present results show that ACTH responses induced by intravenous injection of IL-1α were suppressed by systemic pretreatment with indomethacin and that intrahypothalamic injection of PGE2 stimulates the secretion of ACTH. Furthermore, systemic pretreatment with anti-CRF antibody significantly suppressed the ACTH response induced by intrahypothalamic injection of PGE2. These data suggest that the ACTH response induced by IL-1 is mediated by CRF secretion stimulated by hypothalamic PGE2.
TL;DR: Data indicate that all steroid hormones exert direct actions on the cardiovascular system at its different levels of organization, thus enabling adjustment to the changing demands during reproduction, stress, and solar seasons (vitamin D-soltriol).
Abstract: Knowledge of steroid hormone sites of action and related effects in cardiovascular and neural regulatory tissues is reviewed. Evidence for nuclear receptor sites is derived mainly from autoradiographic studies with relatively intact tissues and some biochemical studies with tissue homogenates. In the heart and in the walls of blood vessels, estradiol, dihydrotestosterone, corticosterone, aldosterone, dexamethasone, and soltriol (vitamin D) show nuclear binding. In the brain and spinal cord, neuronal regions associated with cardiovascular regulation contain nuclear receptors in specific patterns for each steroid hormones, including progesterone and soltriol. These data indicate that all steroid hormones exert direct actions on the cardiovascular system at its different levels of organization, thus enabling adjustment to the changing demands during reproduction (gonadal steroids), stress (adrenal steroids), and solar seasons (vitamin D-soltriol).
TL;DR: Radial cells, that in mammals disappear as neurogenesis comes to an end, persist in the adult avian brain and may be the progenitors of new neurons.
Abstract: Adult neurogenesis in birds offers unique opportunities to study basic questions addressing the birth, migration and differentiation of neurons. Neurons in adult canaries originate from discrete proliferative regions on the walls of the lateral ventricles. They migrate away from their site of birth, initially at high rates, along the processes of radial cells. The rates of dispersal diminish as the young neurons invade regions devoid of radial fibers, probably under the guidance of other cues. The discrete sites of birth in the ventricular zone generate neurons that end up differentiating throughout the telencephelon. New neurons may become interneurons or projection neurons; the latter connect two song control nuclei between neostriatum and archistriatum. Radial cells, that in mammals disappear as neurogenesis comes to an end, persist in the adult avian brain. The presence of radial cells may be key to adult neurogenesis. Not only do they serve as guides for initial dispersal, they also divide and may be the progenitors of new neurons.
TL;DR: Investigation of cytosolic proteins from three plants revealed striking homologies and conserved domains which are probably involved in their function as LTPs, which could play a major role in membrane biogenesis.
Abstract: Plant cells contain cytosolic proteins, called lipid transfer proteins (LTP), which are able to facilitate in vitro intermembrane transfer of phospholipids. Proteins of this kind from three plants, purified to homogeneity, have several properties in common: molecular mass around 9 kDa, high isoelectric point, lack of specificity for phospholipids, and binding ability for fatty acids. The comparison of their amino acid sequences revealed striking homologies and conserved domains which are probably involved in their function as LTPs. These proteins could play a major role in membrane biogenesis by conveying phospholipids from their site of biosynthesis to membranes unable to form these lipids. Immunochemical methods were used to establish an in vivo correlation between membrane biogenesis and the level of LTP or the amount of LTP synthesized in vitro from mRNAs. The recent isolation of a full-length cDNA allows novel approaches to studying the participation of LTPs in the biogenesis of plant cell membranes.
TL;DR: The role of laminin in neuronal movement given the present concept of the extracellular matrix molecules and their proposed interactions is discussed.
Abstract: During brain development, both neuronal migration and axon guidance are influenced by extracellular matrix molecules present in the environment of the migrating neuronal cell bodies and nerve fibers. Glial laminin is an extracellular matrix protein which these early brain cells preferentially attach to. Extracellular glycosaminoglycans are suggested to function in restricting neuronal cell bodies and axons from certain brain areas. Since laminin is deposited along the radial glial fibers and along the developing nerve pathways in punctate form, the punctate assemblies may be one of the key factors in routing the developing neurons in vivo. This review discusses the role of laminin in neuronal movement given the present concept of the extracellular matrix molecules and their proposed interactions.
TL;DR: Araplysillins-I and-II, two novel dibromotyrosine derivatives, were isolated from Psammaplysilla arabica and their structure was elucidated by spectroscopic methods and proved to be inhibitors of Na+/K+ ATPase and to have antimicrobial activity.
Abstract: Araplysillins-I and-II, two novel dibromotyrosine derivatives, were isolated fromPsammaplysilla arabica and their structure was elucidated by spectroscopic methods. They proved to be inhibitors of Na+/K+ ATPase and to have antimicrobial activity.
TL;DR: The discovery of an aminophospholipid translocase in chromaffin granules proves that eukaryotic organelles may also contain lipid translocators.
Abstract: Membranes allow the rapid passage of unchanged lipids. Phospholipids on the other hand diffuse very slowly from one monolayer to another with a half-time of several hours. This slow spontaneous movement in a pure lipid bilayer can be selectively modulated in biological membranes by intrinsic proteins. In microsomes, and probably in bacterial membranes, non-specific phospholipid flippases allow the rapid redistribution of newly synthesized phospholipids. In eukaryotic plasma membranes, aminophospholipid translocase selectively pumps phosphatidylserine (PS) and phosphatidylethanolamine (PE) from the outer to the inner leaflet and establishes a permanent lipid asymmetry. The discovery of an aminophospholipid translocase in chromaffin granules proves that eukaryotic organelles may also contain lipid translocators.
TL;DR: A theory is proposed which describes how sterols and other membrane reinforcing molecules might have driven the evolution of intracellular membranes, thus establishing the dynamic membrane system of modern eukaryotes.
Abstract: Sterols are acquired by cells either biosynthetically by the interaction of cytoplasmic and endoplasmic reticulum elements, or by endocytosis. The subcellular distribution of sterols, however, argues that sterols are trafficked quickly from sites of acquisition to target membranes, particularly the plasma membrane. The mechanisms mediating this movement might include aqueous diffusion, vesicles of either a unique pathway or of the protein secretory pathway, or carrier proteins. These mechanisms are discussed and the limited data concerning each are presented. Finally, a theory is proposed which describes how sterols and other membrane reinforcing molecules might have driven the evolution of intracellular membranes, thus establishing the dynamic membrane system of modern eukaryotes.
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TL;DR: Hoffmann and Schmidt-Koenig as mentioned in this paper showed that birds trained at medium northern latitudes were able to allow for the sun's apparent movement north of the arctic circle, but not in equatorial and trans-equatorial latitudes.
Abstract: The sun compass was discovered by G. Kramer in caged birds showing migratory restlessness. Subsequent experiments with caged birds employing directional training and clock shifts, carried out by Hoffman and Schmidt-Koenig, showed that the sun azimuth is used, and the sun altitude ignored. In the laboratory, McDonald found the accuracy to be ±3° – ±5°. According to Hoffmann and Schmidt-Koenig, caged birds trained at medium northern latitudes were able to allow for the sun’s apparent movement north of the arctic circle, but not in equatorial and trans-equatorial latitudes.
TL;DR: Several physiological states, including insemination, age, and nutrition, can modulate both host-seeking and pre-oviposition behaviors, which are discussed in this review.
Abstract: Most female mosquitoes require a meal of blood that provides protein for egg maturation. For reproduction to occur, two behavioral sequences are essential. One is concerned with finding a host for the blood meal and the other in finding a site on which to lay the eggs that result. Stimuli from both hosts and oviposition sites initiate the reproductive behaviors of host-seeking and pre-oviposition, respectively, that are discussed in this review. After sensory receptors perceive these stimuli, the central nervous system must integrate the information and associate it with a biologically appropriate response. Host-seeking appears to be the default behavior, expressed whenever host stimuli are present. However, if the female is successful in locating a host and ingesting blood, subsequent host-seeking is inhibited when the meal distends the abdomen above a certain threshold. Host-seeking inhibition continues during egg development as a result of a humoral mechanism even after the blood volume has been reduced by digestion. At the time when eggs are maturing and host-seeking is inhibited, pre-oviposition behavior predominates if the central nervous system receives oviposition site stimuli. This behavior is also initiated by a humoral factor. Several physiological states, including insemination, age, and nutrition, can modulate both host-seeking and pre-oviposition behaviors.
TL;DR: Although one can measure the organic matter in various ecosystems in terms of organic carbon, this measurement does not indicate what portion of the organic carbon is bioavailable to the microorganisms, many species of bacteria will form ultramicrocells and enter a physiological state known as starvation-survival.
Abstract: Although one can measure the organic matter in various ecosystems in terms of organic carbon, this measurement does not indicate what portion of the organic carbon is bioavailable to the microorganisms. Most organic matter is recalcitrant and, therefore, most microorganisms do not have sufficient energy to carry on their metabolism for growth and reproduction. As a result, many species of bacteria will form ultramicrocells and enter a physiological state known as starvation-survival. This physiological state results in metabolic arrest which permits the organisms to survive for long periods of time without sufficient energy for growth and reproduction.
TL;DR: PNL-TP, which is identical to sterol carrier protein 2, transfers all common phospholipids, cholesterol and oxysterol derivatives between membranes, is very efficient in mediating a net mass transfer of lipids to lipid-deficient membranes.
Abstract: We have described the mode of action of the phosphatidylcholine transfer protein (PC-TP), the phosphatidylinositol transfer protein (PI-TP) and the non-specific lipid transfer protein (nsL-TP) isolated from bovine and rat tissues. PC-TP and PI-TP specifically bind one phospholipid molecule to be carried between membranes. PC-TP, and most likely PI-TP as well, have independent binding sites for the sn-1- and sn-2-fatty acyl chains. These sites have different properties, which may explain the ability of PC-TP and PI-TP to discriminate between positional phospholipid isomers. nsL-TP, which is identical to sterol carrier protein 2, transfers all common phospholipids, cholesterol and oxysterol derivatives between membranes. This protein is very efficient in mediating a net mass transfer of lipids to lipid-deficient membranes. Models for its mode of action, which is clearly different from that of PC-TP and PI-TP, are presented.