Showing papers in "International Review of Cytology-a Survey of Cell Biology in 1976"
TL;DR: It was found that the differentiation features characteristic of mechanocytes of the source tissue are consistently retained by in vitro descendants of clonogenic cells, thus self-maintained precursors determined to differentiate into definite types of mechanocyte are present in postnatal life.
Abstract: Publisher Summary This chapter discusses precursor cells of mechanocytes. Among the cells of connective tissue, precursors of mechanocytes capable of protracted self-maintenance can be identified by the in vitro colony assay method. They behave as clonogenic cells and give rise to diploid strains of fibroblasts capable of sustained passaging. In cases in which reverse grafting in vivo was carried out, it was found that the differentiation features characteristic of mechanocytes of the source tissue are consistently retained by in vitro descendants of clonogenic cells. Thus self-maintained precursors determined to differentiate into definite types of mechanocytes are present in postnatal life. For clones of mechanocytes from hemopoietic organs a distinguishing property may be the type of inductive microenvironment they create. Beside interorganic differences in the microenvironment, intraorganic ones are obviously present. This is evidenced by the persistence of thymus-dependent and thymus independent zones in lymphoid organs and of regions in the spleen where erythroid colonies occur more frequently than myeloid ones. Stem cell existence has been established unambiguously for tissues with extensive cell renewal. Mechanocytes, on the contrary, have a very slow renewal rate. During the life-span the total number of cell divisions mechanocyte precursors undergo is considerably smaller than that of hemopoietic or lymphoid precursor cells. Therefore it is not excluded that structurally the population of progenitors of mechanocytes will appear fundamentally different as compared to the population of hemopoietic cells.
743 citations
TL;DR: This chapter discusses germ plasm and the differentiation of the germ cell line and the histochemical evidence for the presence of RNA in polar granules of insects and germinal plasm of amphibians indicates that RNA is present only in eggs and early embryos, while a protein component is present throughout the germ cycle.
Abstract: Publisher Summary This chapter discusses germ plasm and the differentiation of the germ cell line. Germ plasm is defined as a substance present in the cytoplasm of gametes, which is segregated into specific cells during blastulation and determines that those cells shall become the progenitors of the germ cell line during subsequent development. The composition of germ plasm is discussed. The histochemical evidence for the presence of RNA in polar granules of insects and germinal plasm of amphibians indicates that RNA is present only in eggs and early embryos, while a protein component is present throughout the germ cell cycle. Good morphological and experimental evidence for the presence of germ plasm is available for only a few animal species. The germinal cells of chaetognaths were present in early stages of embryonic development and identified a group of cells at the bottom of the archenteron cavity in gastrulas of Sagitta as the primordium of the germ line. Experimental studies are given to determine the role of germinal plasm in anuran eggs by altering the cytoplasm in which it is contained.
599 citations
TL;DR: The nucleusolus is organized at the nucleolus-organizing region of the chromosomes, which are generally visible as secondary constriction regions in metaphase chromosomes, and the chromatin within the constriction region is lost at interphase inside the nucleoli.
Abstract: Publisher Summary The nucleolus is organized at the nucleolus-organizing region of the chromosomes, which are generally visible as secondary constriction regions in metaphase chromosomes. The chromatin within the constriction region is lost at interphase inside the nucleolar mass. The chromatin is highly extended at this stage. At the ultrastructural level, the nucleolus has at least three components: (1) a granular component consisting mainly of ribonucleoproteins (RNP) granules—pars granulosa, (2) a fibrillar component, consisting of RNP fibrils—pars fibrosa, and (3) chromatin elements. Chromatin elements may be present in three forms: (1) nucleolus-associated chromatin, which most likely does not take part in nucleolus formation; however, the possibility of its association with condensed inactive ribosomal cistrons, at least in some cells, cannot be overruled at present, (2) septalike intranucleolar chromatin, and (3) isolated or dispersed intranucleolar chromatin threads. Intranucleolar chromatin is often associated with the pars fibrosa. Identical components can also be found in isolated nucleoli. Studies on the nucleoli in giant chromosomes indicate that the intranucleolar chromatin in these nucleoli is present as puffs of different sizes. The nucleolar chromatin is not an autonomous structure of the nucleolus but is a continuous structure and part of the nucleolar chromosome.
372 citations
TL;DR: This chapter discusses the structure and properties of thecell surface coat, a relatively strong, hydrophilic coat which is a permanent feature of the cell surface complex.
Abstract: Publisher Summary This chapter discusses the structure and properties of the cell surface coat. Cell surface coats have been found on all living cells that have been examined with sufficiently sensitive methods. These cells protect their fragile plasma membrane with a relatively strong, hydrophilic coat which is a permanent feature of the cell surface complex. Under special conditions, however, rarely and momentarily, these coats can be breached or even removed from certain cells to reveal the delicate, oily, liquid like layer of the plasma membrane, damage to which is lethal unless immediately repaired. These cells usually are able to replace their missing coats in a matter of minutes. Most animal cell coats appear in the electron microscope (EM) as a uniform layer at the external cell surface. The layer seems to originate at, or be a part of, the outer leaflet of the trilaminar plasma membrane, and usually is 100-200 A thick. A variety of methods has been developed to reveal the ultrastructure of cell coats, the details of which depend on the particular method employed. The strength or durability of the cell surface coat varies dramatically among various cells.
230 citations
TL;DR: The developmental responses of urogenital organs to sex hormones are not strictly epithelial phenomena, but are interactive processes dependent on both the epithelium and stroma.
Abstract: Publisher Summary This chapter discusses the epithelial-stromal interactions in development of the urogenital tract. The hormonal influences on urogenital morphogenesis, differentiation, and function are discussed. The hormone-dependent development of the urogenital tract occurs via an interaction between epithelium and stroma in which the stroma plays a decisive role in mediating the unique morphological response of epithelium to sex hormones by inducing specific patterns of epithelial morphogenesis. Through stromal induction, which has been demonstrated during pre and postnatal periods and even into adulthood, the developmental fate of the epithelium is usually determined during fetal or early neonatal periods. However, once determined, urogenital epithelia continue to require a relatively specific interaction with urogenital stroma for full expression of morphogenesis, cytodifferentiation, and function. The developmental properties of epithelium and stroma, which vary temporally, account for changes in hormonal responsiveness of the intact target organs. Thus the developmental responses of urogenital organs to sex hormones are not strictly epithelial phenomena, but are interactive processes dependent on both the epithelium and stroma.
220 citations
TL;DR: Signs that possible intermediates in the evolution of the mitotic apparatus still exist among living organisms, rather than having been casualties of the selective process, gives idea that some of the unusual patterns of nuclear division of other lower organisms such as euglenoids, trypanosomes, ciliates, fungi, and sporozoa are of evolutionary significance.
Abstract: Publisher Summary This chapter discusses the evolution of the mitotic spindle. The recounting of the evolutionary past of the mitotic processes of chromosome movement would entail tracing a gradual shift from membranes to micros as the primary producer of forces for chromosome movement. In addition, it was suggested, microtubules themselves might in the course of evolution have acquired the capacity for force production as an adjunct to preexisting static properties. That at least remnants of some of the intermediate stages in such transitions probably survive in unusual forms of nuclear division should be apparent from the foregoing account. Thus it is find among these not only organisms such as C. cohnii in which membrane phenomena may exert the sole direct force for chromosome movement, but also forms such as hypermastigote flagellates in which membranes and microtubules may both take a direct role in chromosome movement. There are certainly indications that microtubules can assume roles in nuclear division quite unrelated to force production, as in C . cohnii in which a cytoskeletal role for the exclusively extranuclear microtubules seems most likely, and in Syndinium sp . in which chromosomal microtubules effect a permanent connection of kinetochores and poles but seem not to function actively in chromosome movement. Such signs that possible intermediates in the evolution of the mitotic apparatus still exist among living organisms, rather than having been casualties of the selective process, gives idea that some of the unusual patterns of nuclear division of other lower organisms such as euglenoids, trypanosomes, ciliates, fungi, and sporozoa are of evolutionary significance.
181 citations
TL;DR: There is evidence from cytogenetic studies that stem cells differentiating into lymphocytes differ from the so-called pluripotent cells which give rise to myeloid cell lines.
Abstract: Publisher Summary This chapter deals with ultrastructural and cytochemical studies of human normal hemic cells, excluding a detailed analysis of pathological maturation. However, two types of abnormalities involving specific organelles of maturing cells are described (mitochondria with iron accumulation in erythroblasts, and crystalline granules in some leukemic granulocytes). Most of the maturation steps of immunocytes take place outside the bone marrow, that is, in the thymus and in other lymphoid tissues, and very few data are available that can distinguish on an ultrastructural basis between marrow lymphocytes and others. Furthermore, there is evidence from cytogenetic studies that stem cells differentiating into lymphocytes differ from the so-called pluripotent cells which give rise to myeloid cell lines. Numerous studies have been developed for the detection of enzymatic activities in monocytes operating in the process of intracellular digestion that follows endocytosis. At the light microscope level many reactions are available, some of which may be used as specific markers for cell line. At the ultrastructural level, cytochemical studies have established that enzymatic activities are segregated in the endoplasmic reticulum and the golgi complex, and stored into granules. With available techniques, peroxidase and some hydrolases can be detected.
154 citations
TL;DR: The cytological basis for the development of estrogen-independent vaginal proliferation and cornification is discussed, with attention to its implication in tumorigenesis.
Abstract: Publisher Summary Since the vaginal-smear method for determining the stages of the estrous cycle was established in rats by Long and Evans, this technique has become indispensable for investigations of the hypothalamo-hypophysio-ovarian system in rats and mice The vaginal epithelium responds to estrogen, progestin, or androgen, showing either proliferation and cornification or mucification Fully cornified smears indicate the estrous state caused by estrogen from endogenous or exogenous sources The epithelium reversibly responds to estrogen and becomes atrophic in its absence Thus, proliferation and cornification of the vaginal epithelium have long been considered a reliable criterion of the estrous state caused by estrogen in laboratory rodents In 1936, Pfeiffer demonstrated that transplantation of testes of newborn male rats into littermate females induces a persistent-estrus state when they became adults Neither ovulation nor luteinization takes place in the ovaries of these animals A similar persistent-estrus state is also induced by neonatal administration of androgen or estrogen to rats and mice; this state is called the “early androgen or estrogen syndrome” Vaginal cornification continues in persistent-estrus animals but ceases following ovariectomy Accordingly, persistent vaginal cornification is an ovary-dependent (estrogen-dependent) phenomenon because of permanent changes in sexual differentiation of the hypothalamus However, ovary-independent (estrogen-independent) persistent vaginal cornification has recently been demonstrated in rats and mice treated neonatally with estrogen or androgen In this chapter, the cytological basis for the development of estrogen-independent vaginal proliferation and cornification is discussed, with attention to its implication in tumorigenesis
139 citations
TL;DR: This chapter discusses the response of mammary cells to hormones, which reveals that the mammary epithelium in a culture medium responds to combinations of hormones similar to those needed in vivo.
Abstract: Publisher Summary This chapter discusses the response of mammary cells to hormones. The mammary gland offers unique opportunities for studying the molecular mechanisms of hormone action, because it is an organ with exceptional biosynthetic capabilities and an organ that is perhaps the most complex multiple hormone target organ in the mammalian body. Studies with explants of mammary tissue fragments or the entire gland also reveal that the mammary epithelium in a culture medium responds to combinations of hormones similar to those needed in vivo. This responsiveness of the mammary cell to hormones in a serum-free culture medium provides a useful tool for elucidation of the molecular mechanisms involved in specific responses to the synergistic action of steroid and polypeptide hormones. The molecular responses of the mammary cells so far studied mainly measured the synthesis and cellular concentration of the macromolecules. Characterization of these hormone-responsive molecular events with respect to specific biological control mechanisms in the mammary gland remains to be accomplished. The link between such molecular events and the physiology of the gland has been so far studied using inhibitors of nucleic acids and protein synthesis.
131 citations
TL;DR: This chapter discusses the neurosecretion by exocytosis, a theory based on the selective staining of secretory substances within some neurons of the central nervous system that suggests that hormone and binding protein share a common precursor.
Abstract: Publisher Summary This chapter discusses the neurosecretion by exocytosis. The neurosecretion theory was based on the selective staining of secretory substances within some neurons of the central nervous system. Typical neurosecretory cells appear to offer special advantages for the study of controlled membrane fusion. Their secretory and electrophysiological activities lend themselves to experimental manipulation, and the elements are of a convenient size for electron microscope analysis. Neurophysins are synthesized and stored within neurosecretory granules, together with their hormone. Although hormone and neurophysin may interact noncovalently, evidence obtained by Sachs and co-workers strongly suggests that hormone and binding protein share a common precursor. Neurophysin, together with the hormone, travels down the axon from the cell body in the hypothalamus to the posterior pituitary at a rate of at least 2-3 mm per hour in the rat. Observations on the role and fate of neurophysin are also, however, relevant when exocytosis is under consideration.
126 citations
TL;DR: Cell size, the nucleocytoplasmic ratio, and the DNA content of the nucleus are mutually interdependent and it is justifiable to use the data on one of these features for the approximate determination of the others.
Abstract: Publisher Summary Cell size, the nucleocytoplasmic ratio, and the DNA content of the nucleus are mutually interdependent. It is, therefore, justifiable to use the data on one of these features for the approximate determination of the other two. In the evolutionary process, every factor that favors a change in one of these characters influences the state of the other two. For vertebrates, the primitive DNA content was probably not very different from the actual state in Latimeria , many elasmobranchs, and some anurans. It is moderately reduced in mammals. In Dipnoi and Urodela , DNA content and cell size are greatly increased. A reduction in both these features occurred in reptiles, birds, and the majority of teleosts. Regularities occur in the cell size of passerine birds, which suggest that they are indispensable for a high metabolism. The diverse levels of cell-size variability in other vertebrates demonstrate that natural selection may be indifferent to changes in cell size unless they are fairly pronounced. Natural selection could have decreased cell size and DNA content when it favored a decrease in overall size of the organism, speed of development, high metabolism, and rejection of unused genetic information. An increase in DNA content and in cell size could be favored as a means of economizing in structural material with an enlargement of the body and a reduction in maintenance costs. It could confer a greater resistance of cells to changes in the composition of body intercellular fluids.
TL;DR: In this paper, the morphogenesis of staphylococcus aureus cell wall under normal conditions and under the influence of some antibiotics, mainly chloramphenicol and penicillin, is discussed.
Abstract: Publisher Summary For several reasons, there is an increasing interest in studies concerning the morphogenesis of bacterial cell walls. Apparently, Escherichia coli is at the center of interest, but data on several gram-positive bacterial cell walls have also been published, and some excellent reviews on this subject exist. However, the morphogenesis of one of the more complicated and even rather exceptional cell-wall systems—that of staphylococci—deserves to be considered. This chapter discusses the morphogenesis of the staphylococcal cell wall under normal conditions and under the influence of some antibiotics, mainly chloramphenicol and penicillin. For all the studies discussed in the chapter, laboratory strains of Staphylococcus aureus were used, which proved to be especially sensitive to antibiotics and are therefore widely used as test strains for testing sensitivity to antibiotics. These strains are well known as S . aureus SG 511 Berlin and S . aureus SG 511 Hoechst. Much of the data presented in this chapter have not been published before. Several schematic drawings are presented, not only to summarize findings and to make results as clear as possible but also to initiate more precise questions and more sophisticated experiments that could lead to further progress in knowledge on this interesting subject.
TL;DR: The wide variety of reactions of cells from different origins has led to the concept that cAMP is capable of turning on those mechanisms for which the cell has been genetically programmed, and when these cells undergo malignant change, sensitivity to cAMP control of growth reappears, and only those cells that can overcome this control go on to produce tumors.
Abstract: Publisher Summary The studies reviewed in this chapter make it clear that adenosine 3 ' ,5 ' -monophosphate (cyclic AMP, cAMP) regulates or affects a great number of the properties of cells that are measurable in culture The multiple effects of cAMP probably indicate that nature has used this molecule for regulatory functions rather frequently The ubiquitous occurrence of cAMP from bacteria to mammalian cells, and the common thread of cAMP as a regulator of specific functions in different cell types, points out the uniqueness of its role The wide variety of reactions of cells from different origins has led to the concept that cAMP is capable of turning on those mechanisms for which the cell has been genetically programmed When these cells undergo malignant change, however, sensitivity to cAMP control of growth reappears, and only those cells that can overcome this control go on to produce tumors
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TL;DR: This chapter discusses the ultrastructure of vegetative nuclear division, that is, mitotic divisions occurring in the vegetative phase of the fungi and closely related groups.
Abstract: Publisher Summary This chapter discusses the ultrastructure of vegetative nuclear division, that is, mitosis in fungi and closely related groups. Mitotic divisions occurring in the vegetative phase of the fungi are essentially the same as in higher organisms, although the details are frequently obscured by the small size of the nuclei. Fungi, as commonly understood, are a highly diverse and polyphyletic group of organisms. Some of the organisms commonly grouped with fungi are placed there only because mycologists have traditionally studied them. The interphase nucleus of the fungi is bounded by an envelope composed of two unit membranes and interrupted by nuclear pores. Centriole structure in fungi does not differ in its basic aspects from that found in other eukaryotic organisms; that is, the centrioles are composed of nine triplet sets of microtubules which, at their proximal ends, enclose a cartwheellike structure. The centrioles of fungi occur in pairs (diplosome) and are often, although not consistently, associated with a pocket in the nuclear envelope. Other aspects of mitosis and their possible usefulness in assessing evolutionary relationships have been discussed in the cited studies of Pickett-Heaps.
TL;DR: Consistent with the model, the affinity of troponin for the actin-tropomyosin complex is reduced in the presence of calcium.
Abstract: Publisher Summary This chapter discusses the evolution and function of calcium-binding proteins. Muscle calcium-binding parvalbumin (MCBP) amino acid sequences have been determined for carp, pike, frog, and coelocanth, and rabbit. The troponin “trimer” consists of tropomyosin-binding component (TnT, MW 37,000), an inhibitory component (TnI, MW 23,000), and a calcium-binding component (TnC, MW 17,846). TnT binds to tropomyosin either free or complexed with actin. In addition, the TnC-TnI complex, which is quite stable, binds strongly to actin-tropomyosin in the absence of Ca2+. Consistent with the model, the affinity of troponin for the actin-tropomyosin complex is reduced in the presence of calcium. TnI alone or as the TnI-TnT complex has a weak inhibitory effect on actomyosin ATPase. TnC binds to neither actin nor tropomyosin. Phosphofructokinase catalyzes the phosphorylation of fructose 6-phosphate, thereby forming fructose 1,6-diphosphate. The chapter discusses the mitochondrial enzymes with possible calcium involvement. The activity of kynurenine aminotransferase in intact mitochondria is increased threefold by the addition of 10 -3 M CaCl 2 ; however, calcium has no effect on the solubilized mitochondrial enzyme. These responses, which are hardly unusual for membrane enzymes, are interpreted in terms of enhanced translocation of the substrate, α-ketoglutarate, by Ca2+. Other intracellular enzymes that binds calcium is also discussed.
TL;DR: It is likely that the choroid plexus epithelium elaborates a carefully regulated fluid and, at the same time, participates in the homeostasis of the CSF.
Abstract: Publisher Summary This chapter discusses the structure and function of the choroid plexus and other sites of cerebrospinal fluid (CSF) formation. A considerable volume of the CSF is formed continuously within the cerebral ventricles. The choroid plexuses contribute to this formation, but a significant fraction of the CSF is formed extrachoroidally. The exact contributions of fluid from choroidal and extrachoroidal sites remain to be determined. The elaboration of choroidal fluid probably involves the following steps: filtration of the .blood plasma across fenestrated choroidal capillaries, formation of a protein-rich interstitial fluid within the choroidal stroma, and movement of constituents of the interstitial fluid across the choroidal epithelium by the combined processes of ultrafiltration and active transport. Contributing to the choroid plexus blood-CSF barrier are at least three specialized features: a system of circumferential tight functions joining adjacent epithelial cells; a heterolytic system of pinocytotic vesicles and lysosomes within epithelial cells; and a system of epithelial cell enzymes concerned with the active bidirectional transport of substances between the plasma and CSF. It is likely that the choroid plexus epithelium elaborates a carefully regulated fluid and, at the same time, participates in the homeostasis of the CSF. Evidence exists that the extracellular fluid of the brain is continuously formed across the cerebral endothelium, that it drains in bulk to the adjacent CSF cavities, and that it serves as a vehicle for removing intracerebral metabolites. Overall, there is probably a steady, net addition of new fluid at all points along the pathways of CSF circulation until the major sites of absorption (arachnoid villi) are reached.
TL;DR: The chapter examines the evidence that relates various biological parameters to the functions attributed to small lymphocytes and transitional cells in the population of bone marrow cells designated by many investigators as “lymphoid.”
Abstract: Publisher Summary This chapter discusses the small lymphocytes and transitional cell populations of the bone marrow. Their role in the mediation of immune and hemopoietic progenitor cell function is defined. In endothermic vertebrates the bone marrow is the central organ of hemopoiesis. It is the major source of all types of cellular elements that circulate in the blood. The bone marrow plays a major role in the development of those lymphocytes that function as the precursors of antibody-forming cells. In addition, it contains small lymphocytes competent to engage in cell-mediated immune responses. Moreover, the marrow can generate such cells under various experimental conditions. Lymphocytes of the marrow have also been implicated as pluripotent hemopoietic stem cells. On the whole, modern techniques of experimental hematology have furnished evidence in support of the historic argument, and now it seems clear that hemopoietic stem cells, and progenitor cells with varying degrees of commitment to specific lines of hemopoietic differentiation, are contained in the population of bone marrow cells designated by many investigators as “lymphoid.” The chapter examines the evidence that relates various biological parameters to the functions attributed to small lymphocytes and transitional cells.
TL;DR: This chapter distinguishes among four approaches from the point of view of reproducibility, specificity, resolution, ease of use, and possibility of carrying out further reactions on the same preparation for the ultrastructural distinction of DNA from other biological constituents.
Abstract: Publisher Summary The ultrastructural distinction of DNA from other biological constituents may be accomplished by fundamentally different techniques. This chapter distinguishes among four approaches from the point of view of reproducibility, specificity, resolution, ease of use, and possibility of carrying out further reactions on the same preparation: (1) the ultrastructural study of spread DNA preisolated by differential centrifugation or chemical extraction, (2) the detection of DNA using high-resolution autoradiographic analysis, (3) the specific extraction of DNA by chemical agents, and (4) techniques involving an immunocytochemical approach to DNA detection on tissue-thin sections using ferritin- or peroxidase-labeled antibodies. At the light-microscope level, there are many histochemical reactions that permit the identification of DNA; some have been known since the 1920s and have been intensively investigated. These reactions rely on various properties of this polynucleotide, which allow the coupling of an easily identified reagent to it. The same holds true at the ultrastructural level; various procedures have been proposed for the coupling of a contrast-modifying reagent to the DNA molecule.
TL;DR: The morphological (including ultrastructural) and histochemical features of steroid-secreting gland cells in the ovary of the nonmammalian vertebrate are compared and contrasted with those of various steroid-gland-cell species of the mammalian ovary.
Abstract: Publisher Summary This chapter discusses the recent advances in the morphology, histochemistry, and biochemistry of steroid-synthesizing cellular sites in the nonmammalian vertebrate ovary. In recent years, the steroidal secretions of the nonmammalian vertebrate ovary have also been identified by the use of modern steroid methodology. But correlations of steroidogenic activity with individual cell types or with cellular morphology have been little studied in the ovaries of different classes of vertebrates. However, correlation of histochemical, biochemical, and electron microscope studies on the mammalian ovary has revealed that the sites of steroidogenesis are the theca interna cells of the Graafian follicles, the luteal cells of the corpus luteum, and ovarian interstitial gland cells of thecal origin, which have been shown to possess similar cytological, histochemical, and biochemical features. Their most striking common features are (1) abundant diffuse lipids (lipoproteins) in the cytoplasm, which apparently derive from the abundant ultrastructural agranular endoplasmic reticulum, (2) well-developed cell organelles, especially the pleomorphic mitochondria, which have a complex system of internal cristae that are predominantly tubular, (3) the development of diffuse lipoproteins (or agranular endoplasmic reticulum), closely accompanied by the appearance of enzyme activities indicative of the biosynthesis of steroid hormones, (4) under certain physiological situations, stored lipid droplets in the cytoplasm, which consist of either phospholipids or phospholipids, triglycerides, and cholesterol and/or its esters, and (5) the capacity to form a variety of steroids in biochemical experiments in vitro . In this chapter, the morphological (including ultrastructural) and histochemical features of steroid-secreting gland cells in the ovary of the nonmammalian vertebrate are also compared and contrasted with those of various steroid-gland-cell species of the mammalian ovary.
TL;DR: This chapter explains how the secretory apparatus of accessory sex gland cells is modified to produce their characteristic secretions.
Abstract: Publisher Summary This chapter discusses the morphology and cytology of the accessory sex glands in invertebrates. Gland cells secreting chemically different molecules have been grouped either vertically, each type of gland spatially sufficiently separated from the others and specialized to produce a specific secretion or horizontally, with different secretions being produced by different cells in the same glandular epithelium or by the same cells with or without temporal succession. The complexity of the secretory behavior is well illustrated by L. nuttalli in which the first pair of accessory sex glands of the male produces six different secretions, all of which are used in spermatophore formation. The chapter explains how the secretory apparatus of accessory sex gland cells is modified to produce their characteristic secretions. Gland cells that look alike morphologically may produce different secretions, for example, the ejaculatory duct epithelial cells of Musca secrete at least 12 proteins. A degree of plasticity in the activity of the secretory apparatus may be expected only in these multipotent cells. Accessory sex gland function being indispensable for successful reproduction in nearly all advanced animal groups, it is indeed surprising that correlative studies on the structure, biochemistry, and physiology of the accessory glandular elements are comparatively few.
TL;DR: Observations would confirm the steroidogenic role of the CS, if any, which is one of the three possible roles attributed to the CS based on the available evidence.
Abstract: Publisher Summary This chapter discusses the cytophysiology of corpuscles of stannius (CS). The corpuscles of stannius (CS) are encapsulated epithelial organs associated with the kidneys of teleost fish. Their presence is also observed in the holosteans, amia and lepisosteus, but they have no known homolog in other vertebrates. Synthesis, conversion, and storage of corticosteroids, calcium-ion regulation, and renin secretion are some of the functions attributed to the CS. The chapter discusses the structure and physiology of the cells that comprise the CS. Emphasis is placed on experimental results relating to their function. Anatomical data suggesting the existence of two types of cells in the CS, different tissues organized into similar-looking organs (tubule corpuscles and duct corpuscles), or the same cell performing different functions at different periods await verification on an extensive basis, probably employing electron microscope and cytochemical techniques. If this suspected possibility is found to be true, these studies would constitute a major step in our attempt to understand the function of the CS. These observations would confirm the steroidogenic role of the CS, if any, which is one of the three possible roles attributed to the CS based on the available evidence.
TL;DR: Support for the hypothesis of a ventricular route of delivery awaits evidence that these endogenous releasing hormones found in the CSF of the third ventricle are indeed derived directly from surrounding hypothalamus and that they are delivered through tanycytes into pituitary portal blood.
Abstract: Publisher Summary This chapter discusses the uptake and transport activity of the median eminence of the hypothalamus. Two releasing hormones, thyrotropin-releasing hormone (TRH) and luteinizing hormone releasing hormone (LHRH), have been detected in the cerebrospinal fluid (CSF) of the third ventricle of the rat. Their concentrations can be experimentally altered, and they fluctuate with changes in endocrine status of the animal. Further support for the hypothesis of a ventricular route of delivery awaits evidence that these endogenous releasing hormones found in the CSF of the third ventricle are indeed derived directly from surrounding hypothalamus and that they are delivered through tanycytes into pituitary portal blood. Releasing hormones and other substances experimentally placed in the ventricle are transported through the median eminence and are capable of stimulating release of pituitary hormones. Transport through tanycytes has been visualized by intraventricular infusion of radiolabeled compounds and autoradiography at the electron microscope level. The median eminence may also be a site of feedback effect of gonadal steroids on transport of LRH. The catecholaminergic projections to the median eminence provide both dopamine and norepinephrine as potential mediators of ependymal transport activity.
TL;DR: Results are consistent with cessation of synthesis of tyrosinase and melanosomal structural proteins in BrdU-treated cells, and indicate that there may be a “program” of gene activity for melanogenesis, which is regulated as a unit.
Abstract: Publisher Summary This chapter discusses the effects of 5-bromodeoxyuridine (BrdU) on tumorigenicity, immunogenicity, virus production, plasminogen activator, and melanogenesis of mouse melanoma cells Tumorigenicity and expression of PA appeared to be immediately affected by these changes; there was a lag in the time course of reduction and subsequent regaining of tyrosinase activity The effects of BrdU on total RNA or protein synthesis or on plating efficiency appear insufficient to account for the degree of suppression of function observed Investigations on the suppression of tumorigenicity by BrdU reveal separate components involved in the tumorigenic potential of melanoma cells Both reduction in the intrinsic ability of the cells to grow in vivo and changes evoking host defense mechanisms appear to operate in the reduction of tumorigenicity by BrdU treatment Host response may depend on antigenic changes, some of which may be related to the induction of C-type virus in BrdU-treated cells The untreated melanoma cells grow in a manner suggestive of transformed cells The suppression of melanogenesis by BrdU occurs through a coordinated effect on the structural and enzymic proteins required for melanin synthesis These results are consistent with cessation of synthesis of tyrosinase and melanosomal structural proteins in BrdU-treated cells, and indicate that there may be a “program” of gene activity for melanogenesis, which is regulated as a unit
TL;DR: The correlation of recent electron microscope and histochemical studies on the steroid-synthesizing cellular sites in the ovaries of different groups of nonmammalian vertebrates revealed that they also possess the cytological, histochemical, and biochemical features specific to steroid gland cells of mammalian gonads.
Abstract: Publisher Summary This chapter discusses the recent advances in the morphology, histochemistry, and biochemistry of steroid-synthesizing cellular sites in the testes of nonmammalian vertebrates. The general basic functions of the vertebrate testis are twofold: the production of spermatozoa and the secretion and release of hormones. The most striking common features of steroid producing cells of mammalian gonads are: (1) abundant diffusely distributed lipoproteins in the cytoplasm; (2) abundant membranes of smooth reticulum; (3) mitochondria with predominantly tubular cristae; (4) development of diffuse lipoprotein, accompanied by enzyme activity indicative of the biosynthesis of steroid hormones; (5)under certain physiological conditions, stored cholesterol-positive lipid droplets; and (6) capacity to form a variety of steroids in biochemical experiments in vitro. The correlation of recent electron microscope and histochemical studies on the steroid-synthesizing cellular sites in the ovaries of different groups of nonmammalian vertebrates revealed that they also possess the cytological, histochemical, and biochemical features specific to steroid gland cells of mammalian gonads.
TL;DR: The evolutionary origin of the mitochondria is discussed, which has been illustrated by Dickerson, who correlated sequence changes in cytochromes from diverse organisms with absolute times of phylogenetic divergence obtained from classic paleontological data.
Abstract: Publisher Summary This chapter discusses the evolutionary origin of the mitochondria. Most prokaryotes and essentially all eukaryotes are adapted to life in the presence of free oxygen. The two fundamental biochemical adaptations for such life are the possession of two enzymes, superoxide dismutase and catalase, which protect cellular components from autooxidation, and an electron transport system that allows cells to use atmospheric oxygen as a terminal electron acceptor for energy yielding biochemical oxidations. Evolutionary rates of amino acid or nucleotide substitution have been computed for several macromolecules. Such rates are generally quite constant for any particular molecular phylogeny. This has been illustrated by Dickerson, who correlated sequence changes in cytochromes from diverse organisms with absolute times of phylogenetic divergence obtained from classic paleontological data. According to the symbiotic model, eukaryotic cytoplasm should show evidence of a fundamentally anaerobic nature, since the anaerobic protoeukaryote acquired its oxygen-mediating systems from the aerobic symbiont. Mitochondria contain their own genetic system. This is composed of a specific mitochondrial DNA (mtDNA), as well as the means for its replication and, at least potentially, expression. Thus the organelles possess a DNA-dependent RNA polymerase and a system for protein synthesis, consisting of ribosomes, mRNA(s), tRNAs, aminoacyl-tRNA ligases, and the three classes of protein factors (initiation, elongation, and termination factors) required for its function.
TL;DR: The cytological variability and the many clinical symptoms related to aberrations of late-replicating autosomes show clearly the great significance attached to the mode of action of this chromosome material.
Abstract: Publisher Summary This chapter discusses the variable condition of euchromatin and heterochromatin. Several terms were used to describe late-replicating chromosome material, replacing the customary term heterochromatin which was introduced by Heitz. The varying degree of condensation of meiotic chromosomes was called heteropycnosis. The chapter discusses the structure characterization of late-replicating chromosome material. According to the electron microscope studies euchromatin and heterochromatin both consist of 200-A fibrils but differ either in manner of spiralization or in condensation system. A varying content of nucleic acid and a different degree of spiralization are commonly held responsible for the different stainability. Heterochromatin in the interphase cell nucleus can fuse into one body (the collective chromocenter) or can be distributed in several nuclear regions. The Lyon hypothesis explained several puzzling phenomena and was of great help in the development of human genetics in spite of its deficiencies. Inactivation, however, represents only one aspect of the mode of action of late-replicating chromosome material. The cytological variability and the many clinical symptoms related to aberrations of late-replicating autosomes show clearly the great significance attached to the mode of action of this chromosome material.
TL;DR: The observation of gene dosage effects in 1s-2s hybrids that affect phenotypic expression suggests the existence of an alternative mechanism, based on the production of activator substances contributed by the differentiated parent in limited quantities.
Abstract: Publisher Summary This chapter discusses the control of gene expression in somatic cell hybrids. The chapter discusses cell fusion, namely, the use of this technique to investigate the factors and mechanisms that regulate the expression of differentiated functions in somatic vertebrate cells. Spontaneous fusion of somatic cells in vivo occurs only in a few exceptional cases, representing an event of terminal differentiation. In analyzing a given differentiated trait in a hybrid cell, one has to consider that, for example, an enzyme, although transcribed and translated in the hybrid, might escape detection as a result of inhibition or rapid degradation. Experiments that study the effects of gene dosage on phenotypic expression in hybrids should include quantitative measurements of the rate of gene expression, or at least of the amount of gene product per cell. Otherwise the distinction between the action of an activator or competition for a limited amount of repressor cannot be made. By using experimental systems that allow the quantitative determination of specific mRNA, one can determine the level at which such proposed regulator substances act. Preliminary and promising results have been obtained with myoblasts and with erythroid cells. The observation of gene dosage effects in 1s-2s hybrids that affect phenotypic expression suggests the existence of an alternative mechanism, based on the production of activator substances contributed by the differentiated parent in limited quantities.
TL;DR: The chapter summarizes the main results obtained in the study of mitochondrial transcription with different organisms, those most commonly used being yeast, Neurospora crassa, Tetrahymena pyriformis, HeLa cells, Xenopus, and rat liver.
Abstract: Publisher Summary This chapter discusses the biochemical analysis of mitochondrial transcription and translation. It is well known that mitochondria, like chloroplasts, are semiautonomous organelles. This implies that two genetic systems cooperate in their biosynthesis: an extramitochondrial system and an intramitochondrial system. The extramitochondrial system is formed by the nuclear genome which codes for the majority of mitochondrial proteins through the formation of mRNA translated mostly or completely at the level of the cytoplasmic machinery for protein synthesis. The intramitochondrial system is formed by a mitochondrial genome whose genetic continuity and expression is ensured by the existence, within the organelle itself, of enzymes responsible for DNA and RNA synthesis, and complete protein-synthesizing machinery with properties completely different from those of its cytoplasmic counterpart. Two approaches are used in the study of mitochondrial transcription: studies in vitro and studies in vivo. The chapter summarizes the main results obtained in the study of mitochondrial transcription with different organisms, those most commonly used being yeast, Neurospora crassa, Tetrahymena pyriformis, HeLa cells, Xenopus, and rat liver. The experimental approaches used to study mitochondrial translation products have been reviewed.
TL;DR: This chapter discusses approaches to the analysis of fidelity of DNA repair in mammalian cells, which appears to use the undamaged, complementary strand as a template for nucleotide insertion in restoration of the damaged region.
Abstract: Publisher Summary This chapter discusses approaches to the analysis of fidelity of DNA repair in mammalian cells. The different types of DNA repair includes: (1) photoreactivation, (2) excision and DNA repair synthesis, (3) repair of single-strand breaks, depurinated Sites, and small base adducts, (4) post replication repair and recombination, and (5) host cell reactivation. There are two major approaches to the analysis of fidelity in mammalian cells. The first involves structural (chemical) analysis of restored areas, while the other involves biological evaluation (survival, host cell reactivation, genetic analysis) of cells damaged with various agents. Physical and chemical studies of repair synthesis following excision of damage indicate that in mammalian cells restoration of the damaged region is an orderly accurate process which appears to use the undamaged, complementary strand as a template for nucleotide insertion. An important aspect of repair processes in relation to carcinogenesis is the degree to which these processes themselves may introduce errors that may be carcinogenic. Several studies in bacteria emphasized error-prone and error-free repair processes.
TL;DR: In this chapter, comparisons are made of the different regulatory mechanisms operating in muscles of both vertebrates and invertebrates, and the characteristics of calcium regulation are discussed.
Abstract: Publisher Summary The sliding-filament theory and its supporting evidence are now widely accepted. During muscular contraction, thick and thin filaments do not themselves shorten but instead slide past each other. The relative movement of filaments is thought to be driven by cross bridges projecting from the thick filaments, which in a cyclic and repetitive process attach to and advance along the thin filaments. Associated with the hydrolysis of adenosine triphosphate (ATP), the cross-bridge interaction is thought to generate the force for contraction. In addition to the contractile machinery displayed by the two sets of filaments, muscles must also possess regulatory systems to control their activity. In this chapter, comparisons are made of the different regulatory mechanisms operating in muscles of both vertebrates and invertebrates. The chapter discusses the large body of information on cross bridge–thin filament interaction and the regulation of this interaction in vertebrates. Micromolar amounts of calcium are required for tension development in all the muscles that have been examined, and there is no evidence that any molecule other than calcium triggers contraction. Before discussing the characteristics of calcium regulation, this chapter summarizes the data on the dynamics of cross bridges and what is currently known about their interactions and enzymology. This information serves as a basis for the succeeding discussion of regulation, because it is the cross-bridge cycle that is modulated by changes in the concentration of calcium ions.