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Showing papers in "International Review of Cytology-a Survey of Cell Biology in 1988"


Book ChapterDOI
TL;DR: This chapter provides a comprehensive overview of the current state of knowledge of the research with particular emphasis on evolving concepts of fatty acid binding proteins (FABP) structure, regulation, and function.
Abstract: Publisher Summary This chapter provides a comprehensive overview of the current state of knowledge of the research with particular emphasis on evolving concepts of fatty acid binding proteins (FABP) structure, regulation, and function. Long-chain fatty acids provide the main energy source of most mammalian tissues and also comprise essential components of the structural lipids of cell membranes. The purification of the specific proteins responsible for the low-molecular-weight fatty-acid binding protein activity in different tissues leads to the characterization of three structurally distinct FABP of similar size, each the product of a separate gene. The three cytosolic FABP are generally named according to their tissues of greatest abundance, and comprise liver FABP, intestinal FABP, and heart muscle FABP. A role for the 40-kDa LPM-FABP as a specific cell membrane carrier in the transport of long chain fatty acids into the cells of the liver and possibly other tissues as well is available. The 14- to 15-kDa cytosolic FABPs may function as intracellular acceptors and carriers of long-chain fatty acids and their coenzyme A (CoA) esters, maintaining the ability of the tissues, particularly liver, intestine, heart, and skeletal muscle to utilize fatty acids over wide and acutely varying ranges of flux.

275 citations


Book ChapterDOI
TL;DR: The historical description of Sertoli cells as "nurse cells" thus appears to have been accurate and the nurse-cell function is most clearly demonstrated by the proposed mechanism by which germinal cells obtain ferric ions.
Abstract: As was stated in the introduction, many of the functions of the Sertoli cells are apparently carried out by the protein secretions of these cells. The use of Sertoli cell cultures and appropriate biochemical and immunological techniques has allowed the characterization of some of these secretion products. It is likely that many of the functions of the Sertoli cells are necessary because of the presence of the blood-testis barrier. Many growth and nutritive factors which are necessary for cell viability are available to most cells via the serum. The germinal cells within the adluminal compartment do not have access to serum factors and one of the functions of the Sertoli cells is to synthesize serum-like components and secrete them into the adluminal compartment. The historical description of Sertoli cells as "nurse cells" thus appears to have been accurate. The nurse-cell function is most clearly demonstrated by the proposed mechanism by which germinal cells obtain ferric ions. The Sertoli cells have developed a system to move serum-derived iron through their own cytoplasm and to secrete it bound to newly synthesized testicular transferrin molecules which can deliver it to specific receptors on the germinal cell surface (Huggenvik et al., 1984). Functionally, all of the secreted proteins from Sertoli cells which have been characterized or proposed fall into one of five basic classes. First, Sertoli cells secrete a number of transport proteins including transferrin, ceruloplasmin, and ABP. The proposed function of these proteins is the transport of Fe3+, Cu2+, and androgens to the germinal cells or to the epididymis (ABP). Second, Sertoli cells synthesize and secrete a number of proteins which have a hormone-like or growth factor-like activity. AMH is a clear and well-documented example of this type of product while the evidence for inhibin, somatomedin C, EGF-like growth factor, and seminiferous growth factor will require further corroboration. Third, Sertoli cells secrete proteins which have enzymatic activities. Plasminogen activator is the best characterized example of this class of products and the alpha-lactalbumin-like activity is of potential interest. The fourth class of Sertoli cell secretion products includes those proteins which contribute to the basement membrane, namely, type IV collagen and laminin. Finally, there is a very important group of Sertoli cell secretion products for which there is, as yet, no evidence for a defined function. This group includes SGP-1 and SGP-2 which are the major sertoli cell products in rats and which have been well-characterized biochemically.(ABSTRACT TRUNCATED AT 400 WORDS)

207 citations


Book ChapterDOI
TL;DR: The chapter reveals that potassium uptake is mainly metabolic at low external [K + ] ( M ), while it becomes increasingly nonmetabolic at higher (> 1 m M ) external [ K + ].
Abstract: Publisher Summary This chapter discusses the potassium estimation, uptake, and its role in the physiology and metabolism of flowering plants. Potassium is one of the vital elements involved in inorganic plant nutrition. A number of methods have been developed for the qualitative and quantitative estimation of potassium. It is now feasible to determine accurately K + content even at the cellular level. Two methods are available for the quantitative estimation of K + in situ: electron probe X-ray microanalysis and potassium-sensitive microelectrodes. Electron probe X-ray microanalysis permits the simultaneous quantitative estimation of several elements in a microstructure. In principle, an electron beam is focused on a section of tissue that excites atoms to emit X-rays whose energy is characteristic of the elements. The X-rays are collected in a tune spectrometer, converted to electrical pulses, and counted. Electron probe X-ray microanalysis can also be used for qualitative localization of ions, a technique called X-ray mapping. The chapter reveals that potassium uptake is mainly metabolic at low external [K + ] ( M ), while it becomes increasingly nonmetabolic at higher (> 1 m M ) external [K + ].

188 citations


Book ChapterDOI
TL;DR: This chapter discusses the biochemistry, mechanism, and regulation of secretion along with the functions of the pituitary hormones prolactin (PRL) and growth hormone (GH) and the nomenclature used to describe PLs in various species.
Abstract: Publisher Summary This chapter discusses the biochemistry, mechanism, and regulation of secretion along with the functions of the pituitary hormones prolactin (PRL) and growth hormone (GH). The placentas of numerous species produce hormones that are structurally and functionally similar to the PRL and GH, which are 20–25K molecular weight proteins that regulate various processes, including mammary gland differentiation, steroidogenesis, somatic growth, and intermediary metabolism. The most extensively studied placental PRL-like hormones are the placental lactogens (PLs). The PLs differ from one another in size and primary function, and some species produce more than one hormone that is a PL. The chapter summarizes the nomenclature used to describe PLs in various species. The maternal component of the placenta—the decidua—also produces PRL-like substances in some species. The primate decidua secretes a molecule that appears to be structurally identical to pituitary PRL. The rat decidua produces a substance designated decidual luteotropin, which has PRL-like biological activity but is not identical to rat pituitary PRL.

147 citations


Book ChapterDOI
TL;DR: This chapter reviews the genetic and molecular aspects of maize endosperm development and leads to useful manipulations to gain increased yields and improved quality.
Abstract: Publisher Summary This chapter reviews the genetic and molecular aspects of maize endosperm development The Zea mays L (maize) endosperm development is generated by both its importance in agriculture and by the opportunity it affords to study developmental mechanisms The endosperm of maize is a large storage organ that constitutes 80–90% of the mature kernel dry weight The mature maize kernel is the result of an integrated developmental process involving both the embryo and the endosperm The development of the endosperm is focused as it relates to overall kernel maturation It leads to useful manipulations to gain increased yields and improved quality The maize endosperm is generally described as having a triploid origin and the development of endosperm tissue in the kernel proceeds at a tremendously fast rate The rapidly growing endosperm gradually replaces the nucleus and ultimately compresses any remaining nuclear cells to the outer edge of the kernel cavity Cross-section preparations of the endosperm show the overall structure consisting of irregularly shaped cells with prominent nuclei and nucleoli

132 citations


Book ChapterDOI
TL;DR: This chapter discusses the recent findings of chloroplast degradation and provides an overview of organelle senescence, and discusses a general pattern of temporal changes in the fine structure of different cellular organelles, including chloroplasts.
Abstract: Publisher Summary This chapter discusses the recent findings of chloroplast degradation and provides an overview of organelle senescence. Senescence is the last phase of development of a whole organism, organ, cell, or organelle. It is a degenerative process that leads to the death of a living system. Different tissues and cells of the leaves have their own pattern and timing of senescence. The initiation of senescence in mesophyll cells may not necessarily be synchronized with the process in vascular or epidermal tissues. Even different organelles of a single leaf cell––namely, chloroplasts, mitochondria, endoplasmic reticulum, ribosomes, and the nucleus do not show synchrony in the induction and progress of senescence. The chapter discusses a general pattern of temporal changes in the fine structure of different cellular organelles, including chloroplasts. Chloroplasts are the first organelles to show symptoms of disorganization when all other organelles are normal, followed by a change in the structure of the endoplasmic reticulum and loss of ribosomes. The loss of intrinsic electron transport components should follow the senescence-induced damage to the water-splitting system.

82 citations


Book ChapterDOI
TL;DR: Participation of MTs in the intracellular processes of mature cardiac myocytes is analyzed using the model of cardiac hypertrophy in the rat and an analysis made on the involvement ofMTs in several cellular processes.
Abstract: Publisher Summary This chapter describes the distribution of microtubules (MTs) in various physiopathological states and of their involvement in a broad spectrum of cellular processes. MTs, like actin filaments, are made up of globular protein subunits that can assemble and disassemble rapidly in the cell. The dynamic nature of MTs is highly controlled and their function is directly coupled to the pattern of expression of the different isotypes of tubulins and microtubule-associated proteins (MAPs). A major constituent of the mitotic spindle, MTs influence the distribution of actin filaments, especially during the process of cell division, and of intermediate filaments during cell interphase. MTs play an essential role in the maintenance of cellular shape, in cell movement, and in cellular polarity. Participation of MTs in the intracellular processes of mature cardiac myocytes is analyzed using the model of cardiac hypertrophy in the rat. The chapter describes some characteristics of MTs in adult heart and distribution of MTs within myocytes. There is also an analysis made on the involvement of MTs in several cellular processes.

79 citations


Book ChapterDOI
TL;DR: Immunochemical studies have revealed that gametogenesis and embryonic development of different organisms are accompanied by profound changes in the polypeptide composition of the nuclear lamina, and it is possible that these changes might relate to alterations in the functional organization of nuclei in differentiating cells.
Abstract: Publisher Summary This chapter discusses the contributions of immunochemical approaches to the study of nuclear structure and activity. By segregating the nuclear compartment from the cytoplasm, the nuclear envelope represents the most distinctive feature of a eukaryotic cell. It consists of a double membrane enclosing a 20- to 50-nm-wide perinuclear space. The two membranes are frequently joined and penetrated by nuclear pore complexes, that is, elaborate supramolecular assemblies through which most, if not all, macromolecules are exchanged between nucleus and cytoplasm. The outer nuclear membrane is frequently contiguous with the endoplasmic reticulum and studded with ribosomes, while in most cells the inner membrane is closely associated with chromatin. The nuclear lamina is a fibrillar protein meshwork apposed to the nucleoplasmic surface of the inner nuclear membrane. It is presumed to be important for envelope structure and stability; moreover, it may play a role in organizing the spatial arrangement of interphase chromosomes. Immunochemical studies have revealed that gametogenesis and embryonic development of different organisms are accompanied by profound changes in the polypeptide composition of the nuclear lamina. It is possible that these changes might relate to alterations in the functional organization of nuclei in differentiating cells.

71 citations


Book ChapterDOI
TL;DR: This chapter reviews the chemical and physical information possessed on bacterial surface polysaccharides and determines the extent to which it matches and amplifies the cytological observations of these polymeric structures.
Abstract: Publisher Summary This chapter reviews the chemical and physical information possessed on bacterial surface polysaccharides and determines the extent to which it matches and amplifies the cytological observations of these polymeric structures. The specific groups of extracellular polysaccharides are discussed. Bacterial exopolysaccharide (EPS) are a very diverse series of macromolecules, some of which show a relatively high degree of conservation of structural features. They produce a highly hydrated and an anionic environment immediately surrounding the bacterial cell. It provides the bacteria with a means of complexing cations close to the outer surface. In some polysaccharides, there is a marked specificity for the binding of certain cations. The EPS possess various physical characteristics such as the ability to undergo transition from an ordered to a disordered conformation in solution. The transition is dependent on factors such as the ionic environment, temperature, and the chemical composition of the polymer. The polysaccharides function in adhesion, recognition, and pathogenesis, as well as in prokaryotic development.

53 citations


Book ChapterDOI
TL;DR: The results gathered by normal light microscopy, immunocytochemistry, fluorescent-analog cytochemistry, and electron microscopy allow an improved interpretation of ameboid movement and related phenomena.
Abstract: Publisher Summary This chapter discusses the spatial arrangement, ultrastructural organization, and function of the contractile apparatus in Amoeba proteus as a highly limited portion of the field of cell motility Amoeba proteus grown under normal culture conditions shows various motile activities and cell shapes Active locomotion is always combined with the expression of a distinct polarity, whereas resting cells show a rather apolar organization The contractile system responsible in Amoeba proteus for the generation of motive force for protoplasmic streaming and a large variety of dynamic activities is represented mainly by a thin cortical filament layer at the cytoplasmic face of the cell membrane During normal locomotion, this layer exhibits a distinct structural and physiological polarity with three different zones: a zone of reformation at the front, a zone of contraction in the intermediate cell region, and a zone of destruction at the uroid The results gathered by normal light microscopy, immunocytochemistry, fluorescent-analog cytochemistry, and electron microscopy allow an improved interpretation of ameboid movement and related phenomena

47 citations


Book ChapterDOI
TL;DR: The present development of three-dimensional computer-assisted analysis and the display of nuclear structures in the field of cell biology will lead to a better understanding of both the architecture and functions of the cell nucleus along with its relationships with the cytoplasm.
Abstract: Publisher Summary This chapter reviews the structural aspects and functional significance of spatial relationship between the nucleolus and the nuclear envelope. The descriptive studies of the position of the nucleolus and chromosomes provide interesting data about the relationship between the spatial organization of the nucleus and some of its activities. The position of the nucleolus in the nucleus shows that the nucleoli are located close to or are in contact with the nuclear envelope in dividing somatic animal and plant cells, as well as in gametes. So far, the only cells in which the nucleolus occupies a central position are highly differentiated and do not divide after differentiation. The position of the nucleolus is a consequence of the chromosomal organization characterizing the different cell types. Thus, in plant cells and animal gametes in the early stages of meiosis, the telomeres of the nucleolus organizing regions (NOR)-bearing chromosomes form a small knob of condensed chromatin attached to the nuclear envelope. The present development of three-dimensional computer-assisted analysis and the display of nuclear structures in the field of cell biology will lead to a better understanding of both the architecture and functions of the cell nucleus along with its relationships with the cytoplasm.

Book ChapterDOI
TL;DR: It has been suggested that local synthesis and/or release of transferrin supplies the iron required by rapidly growing cells in situations where the cells do not have ready access to adequate amounts of plasma transferrin due to incomplete development of the vasculature or the presence of blood-tissue barriers.
Abstract: In addition to its role in the activity of specialized proteins such as hemoglobin and myoglobin, iron is required as a cofactor in several important enzymes common to most animal cells. One such enzyme, ribonucleotide reductase, which regulates the production of deoxyribonucleotides during DNA synthesis, requires a continuous supply of iron to maintain its activity throughout the process of DNA replication. The mechanism by which animal cells normally acquire iron involves receptor-mediated uptake of iron-loaded transferrin, followed by release of apotransferrin. The density of transferrin receptors on the cell surface is greatly increased in rapidly dividing normal and neoplastic cells. Various mitogens and certain organogenic tissue interactions have been shown to induce the appearance of transferrin receptors, signalling the onset of DNA replication. Interference with this process of iron delivery causes the rapid arrest of cell cycling, frequently during the S phase itself, which underscores the importance of iron for DNA replication. Although most circulating transferrin is synthesized in the liver and embryonic yolk sac, smaller quantities are produced in several other embryonic organs and certain other adult tissues. It has been suggested that local synthesis and/or release of transferrin supplies the iron required by rapidly growing cells in situations where the cells do not have ready access to adequate amounts of plasma transferrin due to incomplete development of the vasculature or the presence of blood-tissue barriers (Ekblom and Thesleff, 1985; Meek and Adamson, 1985). Oligodendrocytes and Schwann cells have been shown to synthesize and/or contain high concentrations of transferrin and these cells therefore may constitute a local source of this factor for neurons, whose growth and survival in vitro require transferrin. Transferrin in central and peripheral nervous tissues may be significant for the trophic or growth-promoting effect neurons exert on cells of certain tissues. Transferrin duplicates the activity of neural tissue or neural extracts on growth and development of cultured skeletal myoblasts from chick embryos and on proliferation of mesenchymal cells in blastemas from regenerating amphibian limbs, two systems that have been widely used in investigations of the growth-promoting influence of nerves. Moreover, removal of active transferrin from neural extracts, either with antibodies to transferrin or chelation of the iron, inhibits reversibly the effect of the extract in these developing systems. While the physiological significance of the extract in these developing systems.(ABSTRACT TRUNCATED AT 400 WORDS)

Book ChapterDOI
H. Fujita1
TL;DR: The follicular epithelial cell morphologically shows typical exocrine gland cell polarity, synthesizes high-molecular-weight glycoprotein (thyroglobulin) by the rough endoplasmic reticula (RER) and Golgi apparatus system, and releases secretory granules containing thyrogLobulin into the follicular lumen in exocrine cell manner.
Abstract: Publisher Summary This chapter discusses the characteristic ultrastructural and cytochemical functions of the follicular epithelial cell. The relationship between the uniqueness of the secreted hormones and that of the functional morphology of the thyroid gland and the follicular epithelial cell is also discussed. Thyroxine (tetraiodothyronine, T4) and triiodothyronine (T3), secreted from the thyroid follicular epithelial cell, are characteristic hormones because they are special amino acid derivatives (diphenyl ethers) derived from only two molecules of iodotyrosine linked by an ether bond. The follicular epithelial cell morphologically shows typical exocrine gland cell polarity, synthesizes high-molecular-weight glycoprotein (thyroglobulin) by the rough endoplasmic reticula (RER) and Golgi apparatus system, and releases secretory granules containing thyroglobulin into the follicular lumen in exocrine cell manner. Luminal thyroglobulin is usually reabsorbed into the cell by pinocytosis and in stimulated conditions, by phagocytosis as well as pinocytosis. The thyroid is innervated by three kinds of nerve fibers, sympathetic, cholinergic, and peptidergic, although only a few fibers actually enter the organ. The main route for stimulating the follicular epithelial cell to secrete T4 and T3 is humoral, through the thyrotropin-releasing hormone (TRH)- thyroid-stimulating hormone (TSH) system, rather than neuronal.

Book ChapterDOI
TL;DR: This chapter reviews the functional inclusions in prokaryotic cells and site-directed mutagenesis provides valuable information relating to the molecular mechanisms of catalysis and allosteric regulation.
Abstract: Publisher Summary This chapter reviews the functional inclusions in prokaryotic cells. Inclusions are visible expressions of cell metabolism. The inclusion is an integral part of the cell's metabolic machinery, it is important in adjusting the environment of the cell, thereby regulating certain metabolic events, or might represent a product of the cell's metabolism. Gas vesicles are rigid shells of protein that are found in a wide variety of prokaryotic organisms. The protein subunits of the gas vesicle have unique properties that enable their association to result in a structure that is impermeable to water. The genes encoding the structural components of the phycobilisome, gas vesicle, andthe genes for the enzymes involved in glycogen biosynthesis are cloned and sequenced. Site-directed mutagenesis provides valuable information relating to the molecular mechanisms of catalysis and allosteric regulation. The organization of the genes for a given inclusion is determined and is found to be clustered on the chromosome.

Book ChapterDOI
TL;DR: Calcium ions, ATP, and regulative proteins play an essential role in controlling both the interaction of actin and myosin and the sol-gel state of the cytoplasmic matrix.
Abstract: Recent results gathered by normal light microscopy, immunocytochemistry, fluorescent-analog cytochemistry, and electron microscopy have allowed an improved interpretation of ameboid movement and related phenomena. 1. The contractile system responsible in Amoeba proteus for the generation of motive force for protoplasmic streaming and a large variety of dynamic activities is represented mainly by a thin cortical filament layer at the cytoplasmic face of the cell membrane (Fig. 18I). During normal locomotion this layer exhibits a distinct structural and physiological polarity with three different zones: a zone of reformation at the front (A), a zone of contraction in the intermediate cell region (B), and a zone of destruction at the uroid (C). 2. Two types of filaments participate in the formation of the cortical layer: (1) randomly distributed thin (actin) filaments exhibiting a parallel orientation in the anterior (Fc1) and a disordered arrangement in the intermediate and posterior cell region (Fc2; see also Fig. 17b), and (2) thick (myosin) filaments in close association with F-actin and mostly restricted to the intermediate and posterior cell region (Fc2). 3. The internal hydraulic pressure generated by localized active contraction of the cortical layer is transmitted to the endoplasm via the cell membrane and converted into directed streaming by a gel-sol gradient of decreasing viscosity between the uroid and the front. Calcium ions, ATP, and regulative proteins (profilin and a kinase) play an essential role in controlling both the interaction of actin and myosin and the sol-gel state of the cytoplasmic matrix. 4. Any alterations externally induced in the polarity of the cortical filament system by chemical or physical stimulation and inhibition cause immobilization of the amebas (Fig. 18II) with characteristic changes in (1) cell shape (spherulation and cell flattening), (2) membrane dynamics (cytotic and cytokinetic activities), and (3) cytoplasmic organization (hyalogranuloplasmic separation). pseudopodial tip (Fig. 18III, b----c, d----e), (3) destruction of the old layer at the hyalogranuloplasmic border (Fig. 18III, c,e), and (4) alternate solation (Fig. 18III, b and d) and gelation (Fig. 18III, c and e) of the hyaloplasm between the layer and the plasma membrane. The retraction of pseudopodia is accomplished by a local contraction of the cortical layer in conjunction with a simultaneous gel-sol transformation of the ectoplasmic cylinder. 6. The expression of a rather complex cytoskeleton which is composed not only of microfilaments and associated proteins, but also of intermediate- and microtubularlike structures has to be considered in future

Book ChapterDOI
Brian Storrie1
TL;DR: This chapter describes the biochemical concept of accessory proteins—such as receptors—for the targeting of lysosomal proteins to the organelle with the focus on the occurrence of pleiotropic mutations affecting the transport of newly synthesized lysOSomal proteins.
Abstract: Publisher Summary This chapter reviews the assembly of lysosomes from a molecular cell biology perspective and discusses the molecular features of mature forms of lysosomal proteins and their relationship to the biosynthetic origin of the proteins. It also describes the biochemical concept of accessory proteins—such as receptors—for the targeting of lysosomal proteins to the organelle with the focus on the occurrence of pleiotropic mutations affecting the transport of newly synthesized lysosomal proteins and the effect of perturbation of intracellular pH on luminal and membrane protein localization to the lysosome. From these elements, a model for lysosome assembly and its relationship to secretory and endocytic pathways is developed. In this model, the assembly of the lysosomal membrane is considered as the primary event in defining the organelle. The lysosomal components are retained in lysosomes in the face of continuing endocytic trafficking and the process of lysosomal assembly regulation is reviewed. A range of organisms including Paramecium, Tetruhymena, Dictyostelium , yeast, and mammals are used in the experiment. The molecular level of proteins resident within vesicular carriers are selectively targeted to and retained within the lysosome.

Book ChapterDOI
TL;DR: This review has focused on the structural and functional characteristics of those epithelial cells that line the walls of the lower respiratory bronchioles, alveolar ducts, and alveoli and the role of the immune system in responding to the general defense of the lung.
Abstract: This review has focused on the structural and functional characteristics of those epithelial cells that line the walls of the lower respiratory bronchioles, alveolar ducts, and alveoli. In all, five cells types were considered: Clara cells, types I, II, and III pneumocytes, and alveolar macrophages. In addition, a very brief mention of the structure and influence of the basement membrane in alveolar development and repair was included, as well as a brief review of the role of epithelial cells in response to selected deleterious influences. No attempt was made to extend this review to cover the structure and functions of the epithelial lining of the conducting portions of the respiratory system, or the exciting and expanding complexities and interrelationships of the septal stroma. Since the volume of literature encircling this subject has virtually exploded during the last 15 years, it becomes almost impossible to review all reports. However, attempts were made to be selective in citations. Insofar as future developments are concerned, much remains to be understood concerning (1) the responses of all cell types to cytotoxic influences, including their respective abilities to repair induced damage, (2) cell-cell and cell-extracellular matrix relationships in response to injury, (3) the uniqueness of the basement membrane in the lung in controlling permeability and gaseous exchange, (4) the role(s) of alveolar macrophages in response to injury and their relationships to the septal macrophage population, (5) the aberrations in the respective cell types that can give rise to neoplastic growth, and (6) the role of the immune system in responding to the general defense of the lung. Indeed much has been learned in the past 2 decades, and it is expected that a review of this sort 1 or 2 decades hence will elucidate many of the functions and structural modifications of the lung.

Book ChapterDOI
TL;DR: This chapter discusses the interrelation between extracellular adhesion proteins and Extracellular matrix in the reaggregation of dissociated sponge cells.
Abstract: Publisher Summary This chapter discusses the interrelation between extracellular adhesion proteins and extracellular matrix in the reaggregation of dissociated sponge cells Sponges (Porifera) are considered as genuine Metazoa and are placed at the base of the animal kingdom The sponge organism is surrounded by the external epithelium (exopinacoderm), the based epithelial surface (basopinacoderm), and the epithelium of the aquiferous canals The sponges are used for the isolation and purification of the first soluble aggregation factor (AF) The AF is a key molecule in the cell–cell adhesion apparatus The AF-mediated cell–cell adhesion system of Geodia cydonium is heterophilic and of the third order Basically two molecules are involved, the AF and the aggregation receptor (AR) The strength of the interaction between these two molecules is controlled in a tuned manner by enzymatic and nonenzymatic processes The sponges have invented extracellular elements serving as a guiding matrix for an exact positioning of cells It comprises the fluidsolid phase (lectin-glucoconjugate system) and the solid phase (collagen)

Book ChapterDOI
TL;DR: The interactions and fusion of the sperm and egg, changes are initiated that affect virtually all components of the egg cortex and the egg plasmalemma becomes a mosaic composed of membranes derived from the egg and sperm, as well as from dehisced cortical granules.
Abstract: Publisher Summary This chapter describes the structural, chemical, and functional changes of the egg plasma membrane as the results of gamete fusion and cortical granule dehiscence There is a discussion on the investigations examining the fate of the sperm plasma and cortical granule membranes following their fusion with the egg plasmalemma The fundamental mechanisms related to metabolic changes of the activated ovum are also reviewed The processes related to aspects including dynamic changes of the egg cortex and secretory functions of cortical granules during fertilization are focused The interactions and fusion of the sperm and egg, changes are initiated that affect virtually all components of the egg cortex The egg plasmalemma becomes a mosaic composed of membranes derived from the egg and sperm, as well as from dehisced cortical granules Membrane changes reflecting an integration of sperm and egg plasma membranes along the fertilization cone are demonstrated using tracers at the ultrastructural level of observation The shunting of membrane from the egg surface in the form of endocytotic vesicles, to the Golgi complex, and lysosomes are demonstrated by tracer studies

Book ChapterDOI
TL;DR: The chapter outlines a number of the topogenic routes that exist in a typical eukaryotic cell, including the synthesis of quite hydrophobic membrane proteins in the cytoplasm and the translocation across the membranes of an organelle renowned for its selective permeability.
Abstract: Publisher Summary This chapter surveys and evaluates the findings to the identification of precursor forms of import proteins and describes the main stages in import, processing, and other posttranslational modifications into mitochondria. Mitochondrial DNA (MtDNA) encodes only a small minority of the several hundred proteins that go to make up this complex organelle; the rest are specified by nuclear genes, synthesized in the cytoplasm, and transported from the site of synthesis to their final destination. This process involves the passage of the newly synthesized proteins over one or both of the mitochondrial membranes. Such large-scale movement of protein represents one of the major routes for protein targeting (topogenesis) within the eukaryotic cell. This route involves the synthesis of quite hydrophobic membrane proteins in the cytoplasm and the translocation of both these and other quite hydrophilic ones across the membranes of an organelle renowned for its selective permeability. The chapter outlines a number of the topogenic routes that exist in a typical eukaryotic cell.

Book ChapterDOI
TL;DR: Observations lend support to the hypothesis that renin granules are modified lysosomes, which, during metaplastic transformation of vascular smooth muscle cells to epithelioid cells, have acquired the capability to process, condense, store, and release renin upon appropriate stimulation.
Abstract: Publisher Summary The secretory granules of juxtaglomerular cells are endowed with several functional and structural properties, which are otherwise characteristic for lysosomes. These include ultrastructural similarities, autophagic phenomena, the reaction to lysosomotropic agents, the uptake of exogenous tracers, and the coexistence, in these granules, of renin with a variety of lysosomal enzymes. Another facet of this similarity is the close functional and structural relationship between the lysosomal enzyme cathepsin D and renin, both belonging to the family of aspartyl-proteinases, and probably originating from a common ancestor. Taken together, these observations lend support to the hypothesis that renin granules are modified lysosomes, which, during metaplastic transformation of vascular smooth muscle cells to epithelioid cells, have acquired the capability to process, condense, store, and release renin upon appropriate stimulation. In juxtaglomerular cells, it is difficult to identify renin-negative organelles with the ultrastructural characteristics of secondary lysosomes, except for multivesicular bodies, which probably originate from endosomes. It is, therefore, speculated that renin granules are lysosomes thathave acquired the specialized function of renin handling, and have also retained, to some extent, the original lysosomal abilities, such as the uptake and degradation of cellular or foreign material by autophagocytosis or endocytosis, respectively.

Book ChapterDOI
TL;DR: The discovery of NK-1, NK-2, and NK-3-specific alloantigens of NK cells plays a crucial role in defining their subsets and allows a much more rational study of a phenomenon that is defined on the basis of an in vitro functional effect.
Abstract: Publisher Summary This chapter provides an overview of the current status of the surface antigens and markers that are specific for natural killer (NK) cells and others that are not confined to NK cells. As murine NK cells are heterogeneous, the chapter discusses the NK cells recovered from murine spleen that exhibit lytic activity toward lymphoma cells in short-term assays. The chapter considers natural cytotoxic (NC) cells that lyse solid tumor cells in long-term assays, reviews the aspects of putative NK and NC cell lines derived by in vitro culture in interleukin 2 (IL-2) and interleukin 3 (IL-3), and concludes by considering the use of NK cell-specific markers to study a number of important aspects of natural killing. The discovery of NK-1, NK-2, and NK-3-specific alloantigens of NK cells plays a crucial role in defining their subsets and allows a much more rational study of a phenomenon that is defined on the basis of an in vitro functional effect. The chapter discusses problems inherent in treating mice with anti-NK antisera that might not be NK specific, such as anti-asialo-GM I , or sera containing antibodies in addition to specific anti- NK antibodies.

Book ChapterDOI
TL;DR: This chapter provides an overview of the literature concentrating on the early interactions of viruses with sinusoidal and parenchymal cells of the liver in the acute phase of hepatitis.
Abstract: Publisher Summary This chapter provides an overview of the literature concentrating on the early interactions of viruses with sinusoidal and parenchymal cells of the liver in the acute phase of hepatitis. The complex interplay of factors operative in the pathogenesis of viral hepatitis is organized into two categories of viral-host responses. The first viral-host response involves the ability of the virus to adsorb, infect, and replicate in the host tissues with which it comes in contact, dependent on its route of inoculation. In the case of hepatitis, these cells always include hepatocytes, endothelial cells, and lymphoreticular cells that reside in liver, circulation, and extrahepatic lymphoid tissue. The second interaction involves the ability of the host to impede, contain, and finally free itself of the infecting virus. The chapter describes viral-host responses that involve liver-derived cells directly. Many of the viral-host responses may effectively occur before the virus ever arrives at the liver. The lymphoreticular cells in lymph nodes and circulation have important interactions with the virus before it enters liver tissue.

Book ChapterDOI
TL;DR: The rabbit pancreas is quite permeable to relatively large polar nonelectrolytes, such as mannitol, sucrose, and inulin, and may be the leakiest epithelium thus far identified.
Abstract: Publisher Summary This chapter focuses on the experimental work done on one of the epithelial gland, the pancreas, and its permeability to polar nonelectrolytes of substantial size. Epithelial cells form an imperfect, partially selective barrier to the exchange of matter between environment and organism. In addition to the plasma membrane of these cells, matter may enter or leave the organism through spaces between them; these spaces are known as “intercellular spaces” or “paracellular spaces.” The rabbit pancreas is quite permeable to relatively large polar nonelectrolytes, such as mannitol, sucrose, and inulin. In terms of this criterion, it may be the leakiest epithelium thus far identified. The extent of the nonspecific permeability and the fact that it is expressed across cells give a substantially different picture of epithelial leakiness than have studies of planar, predominantly nonglandular, epithelial surfaces. The nonelectrolyte permeability of the rabbit pancreas appears because of the passage of substances directly through the cell's membranes and is not the result of special vesicle transport processes. Permeability is increased several-fold when protein secretion is stimulated.

Book ChapterDOI
TL;DR: The chapter addresses the question of the maintenance of the antigenic homeostasis by autoaggressive lymphocytes, which presumably changes in the genetically determined specific scheme of biosynthetic processes as well as in the antigen pattern—dedifferentiation and/or disdifferentiation.
Abstract: Publisher Summary The concept of immune surveillance over the cytodifferentiation state was formulated on the basis of the data on the discovery of autoaggressive lymphoid cells, the data on the natural antitissue antibodies, and particularly on the analysis of the data on autosensibilization of lymphoid cells in regeneration processes. The role of autoaggressive lymphocytes in immune surveillance is, in many respects, dependent on the level of their activity. A realization of the potentialities of these cells is essential for the maintenance of the scheme of biosynthetic processes and of the antigenic patterns, which are specific for each definitive tissue. The chapter addresses the question of the maintenance of the antigenic homeostasis by autoaggressive lymphocytes. Presumably, there are some changes in the genetically determined specific scheme of biosynthetic processes as well as in the antigen pattern—dedifferentiation and/or disdifferentiation. This is expressed in the appearance of normal cellular antigens, embryospecific, heteroorganic,! and othersin unusual quantities for the definitive tissues. Malignant transformation is a typical example of such deviations; other examples that are not connected with pathology are regeneration and pregnancy. Consequently, the trigger mechanism for realization of autoaggressive potentialities of lymphocytes produces an increased synthesis of some normal cellular antigens in definitive tissues at an unusual time (embryonic proteins) or at an unusual place (ectopic proteins of various kinds, heteroorganic antigens, and isozymes).

Book ChapterDOI
TL;DR: This chapter discusses the relationships between micromorphology and the structural level, and the implications for micronorphology of principles governing symmetric aggregates.
Abstract: Publisher Summary This chapter discusses the relationships between micromorphology and the structural level. Precisely, there is a discussion about the implications for micromorphology of principles governing symmetric aggregates. These principles possess a priori validity from the standpoint of the microscopist. The focus is on the study on biological specimens in their natural context, such as with electron microscopy. The complex and delicate structure of such specimens presents extreme difficulties, resulting in a large gap between the resolution accessible by instrumental power and that relates to specimen organization. This gap is difficult to bridge, but in the case of symmetric aggregates it is provisionally filled by the application of a priori knowledge. The consequences of a symmetry concept are very specific and serve to promote the investigation to prove or disprove the concept, thereby providing a control mechanism of its own. The low-resolution data gain considerably in precision when a comparative study is performed in which use can be made of the clarifying effect of small morphological variations.