Showing papers in "International Review of Cytology-a Survey of Cell Biology in 1994"
TL;DR: The chapter explores the possibility that CSK tensegrity may also provide a mechanical basis for cell locomotion as well as a structural mechanism for coupling mechanical and chemical signaling pathways inside the cell.
Abstract: Publisher Summary This chapter focuses on the role of the intracellular cytoskeleton (CSK) in cell shape determination and tissue morphogenesis. The role of mechanical changes in the CSK during embryological development is reviewed. The chapter focuses on the mechanism by which mechanical forces are transmitted across the cell surface and through the CSK, as well as how they regulate cell shape. An analysis of the biomechanical basis of cell shape control addresses two central questions: (1) how do changes in mechanical forces alter CSK organization, and (2) how do changes in CSK structure regulate cell growth and function. The results from recent studies showing that the CSK can respond directly to mechanical stress are also reviewed. The particular type of mechanical response that living cells exhibit is consistent with a theory of CSK architecture that is based on tensional integrity and is known as “tensegrity”. Inherent to the tensegrity model is an efficient mechanism for integrating changes in structure and function at the tissue, cell, nuclear, and molecular levels. The chapter explores the possibility that CSK tensegrity may also provide a mechanical basis for cell locomotion as well as a structural mechanism for coupling mechanical and chemical signaling pathways inside the cell.
439 citations
TL;DR: Signals, their perception, and transduction in a typical plant defense response is described, which consists of a large number of metabolic changes, including changes in the expression of many different genes that set into motion a complex cascade of events.
Abstract: Publisher Summary Plants are equipped with a wide array of constitutive deterrents that include both toxic chemicals and mechanical barriers. In addition to these, there is a complex system of inducible defense responses aimed at stopping herbivores and pathogens. This chapter describes signals, their perception, and transduction in a typical plant defense response. The defense response consists of a large number of metabolic changes, including changes in the expression of many different genes—that is, a single elicitor signal sets into motion a complex cascade of events, possibly through an array of secondary signals. The extracellular signal compounds involved in triggering defense reactions are known as “elicitors.” The effect of an elicitor is to induce a whole array of responses in a parallel or sequential manner. Elicitors of plant defense responses fall into two categories depending on their source: exogenous and endogenous signals. Exogenous elicitors are the primary signals in plant pathogen interactions. Proteins, oligosaccharides, glycoproteins, fatty acids, and derivatives have been identified that can function as exogenous elicitors. Endogenous elicitors are components of the intercellular signal transduction system of plants.
376 citations
TL;DR: This chapter focuses on the way that changes of intracellular Ca2+ are generated in mammalian eggs, and describes how theseCa2+ changes affect the subsequent development of the embryo.
Abstract: Publisher Summary At fertilization in mammals, the incoming sperm makes two essential contributions to the development of the new organism. One contribution is the DNA and all its associated genes, which enables a diploid organism to develop to full term. The other is the message that triggers egg development. Without this message, delivering the DNA is pointless. In all animal species studied, the message that the sperm delivers is written in the language of cell Ca2+ changes. This chapter focuses on the way that changes of intracellular Ca2+ are generated in mammalian eggs, and describes how these Ca2+ changes affect the subsequent development of the embryo. It is shown that the Ca2+ dynamics at fertilization in mammalian eggs are more complex than in nonmammalian systems. One of the main points that is emphasized is that mammalian eggs are different from other eggs in that they undergo Ca2+ oscillations, or repetitive Ca2+ spikes, during activation at fertilization. One of the central problems to be solved is the triggering mechanism for the oscillations at fertilization. Ca2+o scillations have been described in a vast range of somatic cell types.
294 citations
TL;DR: This chapter discusses lignin and phenolic acids in detail, a description of other phenolic components in the plant cell wall such as cutin and suberin, which are lipophilic polymers.
Abstract: Publisher Summary This chapter focuses on phenolic components of the plant cell wall. Phenol is the structural component common to all phenolic compounds. Both lignin and suberin are phenolic, or phenol-rich polymers, and their role in the life of the plant is well established. The chapter discusses lignin and phenolic acids in detail. There is also a description of other phenolic components in the plant cell wall such as cutin and suberin, which are lipophilic polymers. Sporopollenin is a highly resistant polymer found in the outer pollen wall of higher plants. Lignin is often present in the primary cell walls of fibers, xylem vessels, and tracheids. Lignin can be stained cytochemically by using a range of relatively specific reagents, including phloroglucinol-HCl, which responds to the cinnamaldehyde groups present in lignin. Phenolic compounds can also be detected in situ by their autofluorescence under ultraviolet light. During development, lignification often begins in the middle lamellae and primary cell walls and only later spreads into the secondary wall layers; in other tissues, however, only the secondary walls lignify. The lignin content of tissues can change quantitatively and qualitatively in response to various stimuli.
222 citations
TL;DR: An important concept discussed in this chapter is that the spermatozoon itself may contribute to its own maturation providing that the appropriate conditions of its external milieu are met by the secretory and endocytic activities along the excurrent reproductive duct system.
Abstract: Publisher Summary The epithelial cells of the entire male reproductive duct system, from the testis to the vas deferens, contribute to a proper milieu for sperm maturation through two distinct activities: secretion and endocytosis. Examples are provided in the chapter of these activities by following the origin and fate of SGP-1, SGP-2, and immobilin in the excurrent duct system. These proteins typify the regional variations that exist for the secretion and endocytosis of proteins along the reproductive duct. The reasons for such regional variations in secretion and endocytosis of different proteins ultimately lies in the genetic regulatory factors for each protein, the type of association of each protein with the spermatozoa, if any, and the functional contributions that each protein plays in the final maturation of spermatozoa. An important concept discussed in this chapter is that the spermatozoon itself may contribute to its own maturation (i.e., glycosylation) providing that the appropriate conditions of its external milieu are met by the secretory and endocytic activities along the excurrent reproductive duct system.
166 citations
TL;DR: This chapter includes only the early events of communication between Rhizobia and their host plants, that is, the perception of flavonoid signals by the bacteria, the production of Nod signals by rhizobia, and the early plant responses to the bacteria.
Abstract: Publisher Summary This chapter discusses the Cell and molecular biology of Rhizobium -plant interactions. Soil bacteria, referred to as rhizobia belonging to the genera Rhizobium , Bradyrhizobium , and Azorhizobium , have the unique ability to induce nitrogen-fixing nodules on the roots or stems of leguminous plants. Nodule development consists of several stages determined by different sets of genes both in the host and symbiont. At least at the very early steps of symbiosis, the bacterial and plant genes are activated consecutively by signal exchanges between the symbiotic partners. First, flavonoid signal molecules exuded by the host plant root induce the expression of nodulation ( nod, nol ) genes in Rhizobium in conjunction with the bacterial activator NodD protein. Then, in the second step, lipooligosaccharide Nod factors with various host-specific structural modifications are produced by the bacterial Nod proteins. The Nod factors induce various plant reactions, such as root hair deformation, initiation of nodule meristems, and induction of early nodulin genes, leading to nodule formation. Other classes of bacterial genes are required for successful infection and for nitrogen fixation. This chapter includes only the early events of communication between rhizobia and their host plants, that is, the perception of flavonoid signals by the bacteria, the production of Nod signals by rhizobia, and the early plant responses to the bacteria.
149 citations
TL;DR: It is shown that purely chemical and physical considerations will account for the varieties of pattern the authors notice in natural diatoms, and their living structure appears only to provide the conditions under which the silicious precipitation takes place.
Abstract: An examination of the artificial diatoms shows that purely chemical and physical considerations will account for the varieties of pattern we notice in natural diatoms, and their living structure appears only to provide the conditions under which the silicious precipitation takes place, according to the ordinary laws of chemical action and molecular coalescence [I have tried] to make the subject more intelligible to that, I fear, very numerous class of microscopists who have not paid to Schultze's (1863a,b) artificial diatoms the attention they deserve. (Slack, 1870) The external form of crystals is prismatic, and bounded by straight surfaces which cut each other at certain angles. But the same form is seen in the skeletons of many of the protists, especially the flinty shells of the diatomes and radiolaria; their silicious coverings lend themselves to mathematical determination just as well as the inorganic crystals. (Haeckel, 1905)
136 citations
TL;DR: The hormonal imprinting that occurs at the beginning of the evolutionary sequence retains its role in the higher organisms and influences the maturation of receptors around the period of birth.
Abstract: Publisher Summary This chapter focuses on the origin and development of hormone receptors. Studies of evolution show that there are no unique signal molecules, only those which are selected to be hormones and which are more suitable than others to perform the hormone function. It is also probable that there are no unique hormone receptors, only those structures which are able to recognize the environment. These structures develop into receptors following an encounter with a molecule suitable for signal transmission. Hormonal imprinting occurs at the first encounter of the prospective hormone and the prospective receptor. This results in more specific receptors and more numerous receptors being produced by the cell. The receptors are transmitted to the offspring generations. The hormonal imprinting that occurs at the beginning of the evolutionary sequence retains its role in the higher organisms and influences the maturation of receptors around the period of birth. Imprinting is necessary to complete the program of receptor formation. Imprinting is not age-dependent but depends on the stage of development; it can be developed also in immature, differentiating cells in adults. The recognition system of cells is universal but there are several ways it can be expressed. In each method there are receptors and ligands.
134 citations
TL;DR: A role for MAPs in the establishment and regulation of neuronal form is inferred from their varied, but specific associations with the three principal structural compartments or domains of neurons—namely, axonal, somatic, and dendritic.
Abstract: Publisher Summary This chapter highlights the cellular and subcellular distribution of fibrous microtubule-associated proteins (MAPs) in the vertebrate nervous system It emphasizes on the functional roles of various fibrous MAPs in nervous tissues such as the establishment and maintenance of cellular form, the differentiation of particular types of neuronal and supporting cells in diverse regions of the nervous system, and the generation and regulation of the outgrowth, plasticity, and stabilization of neuronal processes MAPs are nontubulin proteins which copurify to constant stoichiometry with tubulin either during cycles of temperature-dependent microtubule assembly and disassembly or during taxol-stimulated microtubule assembly The major categories of nervous tissue MAPs according to the molecular mass of the principal subunits include: high molecular mass (HMM), intermediate molecular mass (IMM), and low molecular mass (LMM) A role for MAPs in the establishment and regulation of neuronal form is inferred from their varied, but specific associations with the three principal structural compartments or domains of neurons—namely, axonal, somatic, and dendritic Antibodies to some MAPs are frequently used as compartment-specific markers, although there is evidence that all major MAPs are expressed in all three compartments under some circumstances
127 citations
TL;DR: This chapter discusses the physiological and biochemical aspects of cytoplasmic streaming, which is responsible for intercellular transport in Characeae and in the stem of some higher plants.
Abstract: Publisher Summary This chapter discusses the physiological and biochemical aspects of cytoplasmic streaming. Cytoplasmic streaming has been reported in various plant species ranging from algae to higher plants and fungi. the motive force for cytoplasmic streaming in most plant cells is generated by the actin-myosin system, which is also responsible for generating the motive force in muscle contraction and ameboid movement, etc. Cytoplasmic streaming may play an important role not only in intracellular transport but also in other cell functions. In characean cells, it may affect photosynthesis by controlling the transport of ions or substrate through the plasma membrane. Also, cytoplasmic streaming is responsible for intercellular transport in Characeae and in the stem of some higher plants. The mechanism of cytoplasmic streaming is elucidated mostly by experiments using characean cells. It is reasonable to say that the motive force of cytoplasmic streaming in other plant cells is also generated by the same mechanism as that in characean cells, that is, the sliding of myosin associated with organelles along actin filaments using ATP energy.
115 citations
TL;DR: Different criteria can be applied for grouping the photoreceptive organelles of flagellate algae, such as ultrastructural characteristics, the used photoreceptor pigment, the mechanisms involved in primary signal amplification, and extension to low light intensities.
Abstract: Publisher Summary This chapter describes the structural aspects of different photoreceptive organelles including their interaction with cytoskeletal elements. It also examines the mechanisms used for signal generation and modulation, the photoreceptors used and the involved photoelectrical responses, and the currently known elements of the signal transduction or processing chains toward the flagellum. The photoreceptive apparatuses of flagellate algae exhibit an enormous structural variation and result from numerous parallel evolutionary processes. The phototactic systems of flagellate algae, including the sensory transduction chain, are optimized to detect a temporal pattern of light rather than the steady-state light intensity. Proper positioning of the functional eyespot apparatus during cell division is important for signal perception or generation in algal phototaxis and for correct coupling of the photoreceptive apparatus to the signaling effector, the flagellum. Different criteria can be applied for grouping the photoreceptive organelles of flagellate algae, such as ultrastructural characteristics, the used photoreceptor pigment, the mechanisms involved in primary signal amplification, and extension to low light intensities.
TL;DR: This chapter comprises the newer information on nuclearly encoded factors that affect mitochondrial transcription; mRNA processing, stability, and translation; and posttranslational modification and assembly.
Abstract: Publisher Summary This chapter focuses on the regulation of mitochondrial gene expression in yeast ( Saccharomyces cerevisiae ), and tries to explain how these gene expression is regulated. The chapter comprises the newer information on nuclearly encoded factors that affect mitochondrial transcription; mRNA processing, stability, and translation; and posttranslational modification and assembly. Transcription of yeast mitochondrial operons appears to be somewhat more complicated than transcription of phage genes but less complex than E. coli transcription. The 9-bp mitochondrial promoter is positioned immediately upstream of the start of transcription, which is reminiscent of the spacing of the polymerase recognition sequence in T3 and T7 phage genes. Though the mitochondrial enzyme contains two subunits, the catalytic subunit RP041 has considerable sequence similarity to the single subunit T-odd polymerases. With the exception of one transcript, that for a second tRNAthr, mitochondrial transcription units are multigenic. In some cases the initial transcripts contain multiple tRNAs, in other cases combinations of mRNAs and tRNAs or rRNAs and tRNAs. The RNAs involved in mitochondrial translation are all encoded on the mitochondrial genome, including the large and small ribosomal RNAs and the tRNAs.
TL;DR: This chapter summarizes the progress that has been made in determining and understanding the effect of gravity on cell function and describes the results from three general areas of spaceflight research, and within each area, focuses on specific cell systems for which sufficient data have been accumulated.
Abstract: Publisher Summary This chapter summarizes the progress that has been made in determining and understanding the effect of gravity on cell function. It describes the results from three general areas of spaceflight research, and within each area, focuses on specific cell systems for which sufficient data have been accumulated. Included are (1) cell physiology, with a focus on immune cell activation; (2) cell development, with a focus on plant cell differentiation; and (3) the physiology of unicellular organisms. In addition, the chapter describes the underlying principles that govern spaceflight research on the cell, and examines experimental approaches used to investigate the effects of altered gravity on cell function. One environmental factor that has remained constant throughout evolution is the force of earth's gravitational field. The cardiovascular system counteracts gravity when it pumps blood to the upper body, but also uses the pull of gravity when it distributes fluid to the lower extremities. These well-known adaptations to gravity become clearly evident during manned orbital spaceflight, where the inertial acceleration caused by gravitational force is virtually canceled and the gravity vector is no longer detectable. In this microgravity environment, where mass is nearly weightless, astronauts experience space motion sickness, muscle atrophy and bone demineralization, as well as cardiovascular deconditioning and the redistribution and pooling of body fluids in the upper body.
TL;DR: This chapter focuses on plant enzymes known to be regulated by reversible phosphorylation and explores how this mechanism of post-translational modification may serve to coordinate flux through major metabolic pathways.
Abstract: Publisher Summary Protein phosphorylation is considered one of the most studied posttranslational-modification mechanisms affecting protein structure and function. This chapter reviews the regulation of plant enzymes by protein phosphorylation. It focuses on plant enzymes known to be regulated by reversible phosphorylation and explores how this mechanism of post-translational modification may serve to coordinate flux through major metabolic pathways. Most of the enzymes known to be phosphorylated are leaf proteins and the phosphorylation status of many of the phosphoproteins is altered in response to light. Phosphorylation of numerous chloroplast stromal proteins can be observed when intact spinach chloroplasts are provided [32P]Pi in the light or when stromal extracts are given [γ-32P] in vitro. One chloroplast stromal enzyme that undergoes reversible phosphorylation is pyruvate Pi dikinase (PPDK). This enzyme is found in highest activities in leaves of C4 species and in certain crassulacean acid metabolism (CAM) plants, where it plays an important role in photosynthesis by catalyzing the regeneration of phosphoenolpyruvate (PEP), which is the primary CO2 acceptor. The light or dark modulation of PPDK activity in leaves can be mimicked in vitro by an ADP-dependent inactivation and a Pi-dependent activation.
TL;DR: In this article, the authors focused on the isolation and function of human Dendritic cells (DCs) and their relationship with other myeloid cells. But the precise relationships between the DCs found in different tissues and their relationships to other myels remain to be conclusively established.
Abstract: Publisher Summary This chapter focuses on the Isolation and Function of Human Dendritic Cells (DCs) DCs have been delineated in practically every human organ with the exception of the brain and central cornea These tissue-resident DCs are thought to provide an extensive network of sentinel antigen-presenting cells (APCs) capable of antigen capture, processing, and subsequent migration to local lymphoid tissue where efficient primary T-lymphocyte stimulation occurs The work on human DCs has emphasized the close relationship of DCs with other myeloid cells, despite their distinctive morphological and functional properties The precise relationships between the DCs found in different tissues and their relationship to other myeloid cells remain to be conclusively established Identification of DC precursors in human bone marrow and understanding the regulation of tissue migration and differentiation is still in its infancy, but important advances are being made, and are outlined in the chapter
TL;DR: The structure and function of the IF proteins and their oligo- and polymeric forms are compared with a variety of gene-regulatory protein factors and nuclear matrix elements and shown to have many features in common with these compounds.
Abstract: Publisher Summary Intermediate filament (IFs) probably represents one of the last functionally important macromolecular protein assemblies of the eukaryotic cell whose biological role has not yet been unveiled. This chapter discusses the cellular function of IFs, which is based on some characteristic reactivities of their constituent protein subunits with nuclear components in vitro. The structure and function of the IF proteins and their oligo- and polymeric forms are compared with a variety of gene-regulatory protein factors and nuclear matrix elements and shown to have many features in common with these compounds. IF proteins are a class of regulatory DNA binding factors which, in accordance with their developmentally and tissue-specifically regulated expression, may play an important role in cell differentiation as one of their major biological functions.
TL;DR: This chapter discusses membrane and cytoskeleton flow in motile cells with emphasis on the contribution of free-living amoebae.
Abstract: Publisher Summary This chapter discusses membrane and cytoskeleton flow in motile cells with emphasis on the contribution of free-living amoebae. The universal feature of amoeboid cells—independent of their provenance—is the absence of any motor organelles with stable position and permanent structure. In an amoeboid cell, any action leads to the disintegration of the effector and requires its reconstruction in a new location. This endless disassembly–transport–reassembly wheel rotates in each amoeboid cell at all levels of organization: molecular, ultrastructural, and macromorphological. The behavior of the cortical layers of free-living amoebae and amoeboid tissue cells indicates that the cytoskeletal network they contain is in a uniform state of contraction. This contraction results in a continuous and uniform sliding of the cytoskeleton beneath the plasma membrane from the leading edge toward the rear of the cell, or centripetally toward cell-to-substratum attachment sites. The generation of the force needed for this retrograde transport of cytoskeleton is most commonly attributed to the interaction of myosin II or I with the actin network. The actin filaments that compose the submembrane network in amoebae are indirectly connected to a number of integral membrane proteins. Therefore, patches of membrane proteins are hauled by the cytoskeleton in concert with its retrograde or centripetal movement.
TL;DR: This chapter discusses how to detect and locate mechanical stresses in developing embryos and presents some maps of the stresses based on amphibian embryos and some attempts to estimate the range of absolute stress values.
Abstract: Publisher Summary This chapter discusses how to detect and locate mechanical stresses in developing embryos and presents some maps of the stresses based on amphibian embryos The chapter discusses some attempts to estimate the range of absolute stress values The morphogenetic effects of artificial stretching and relaxation of stress in embryonic tissues are also discussed The chapter discusses the role of “surface tension (ST)-like’’ and quasi-elastic components in generating and maintaining stresses One of the simplest and biologically reasonable ways to detect the presence and location of mechanical stresses is to dissect or incise embryonic tissues and trace their deformation immediately after dissection under conditions that prevent the tissue from contracting Rough maps of mechanical stresses can be constructed by making a series of precisely located incisions during successive developmental stages of amphibian embryos At the subcellular level ST-like phenomena may be identified with internalization-resorption (an increase in ST) of cell membrane subunits or the opposite, externalization-insertion (a decrease in ST as far as a negative ST, or surface compression) The first process is usually expressed as endocytosis and the second as exocytosis
TL;DR: This chapter describes some of the unique attributes of flageLLar motors and their potential significance for flagellar function, and highlights some structural, enzymatic, and motility properties of flagllar dyneins that may be common to all family members.
Abstract: Publisher Summary This chapter describes some of the unique attributes of flagellar motors and their potential significance for flagellar function, and highlights some structural, enzymatic, and motility properties of flagellar dyneins that may be common to all family members. Many details of dynein structure have been determined, including the sequence of several subunits and the relationship between sequence and quaternary structure. Much of this information can be applied broadly to cytoplasmic as well as flagellar dyneins, and may ultimately provide insights into general motor enzyme mechanisms. Because of their large size, however, dynein genes may yield their secrets more. easily through traditional in uiuo mutagenesis followed by molecular analysis of the most phenotypically interesting mutants, rather than targeted in vitro mutagenesis and transformation. As ATPase enzymes and as molecular motors, dyneins are unique for their large size, variety, and subunit complexity. Genetic and biochemical dissection of flagellar dyneins has revealed that several similar but unique types are present in any given cilium or flagellum, and that some dyneins contain as many as 3 catalytic heavy chains, each greater than 500 kDa, and up to 12 smaller proteins, while others appear to have a single heavy chain and 2 or 3 smaller subunits.
TL;DR: This chapter focuses on the cytomechanics of the regulation of expression of the differentiated phenotype in retinal pigmented epithelial (RPE) cells and, subsequently, on the process by which RPE cells alter their identity to become other distinct cell types, also known as “cell type conversion” or “ cellular metaplasia.”
Abstract: Publisher Summary This chapter focuses on the cytomechanics of the regulation of expression of the differentiated phenotype in retinal pigmented epithelial (RPE) cells and, subsequently, on the cytomechanics of the process by which RPE cells alter their identity to become other distinct cell types, also known as “cell type conversion” or “cellular metaplasia.” The organization of the cytoskeleton in RPE cells in vitro is a function of cell adhesiveness and substratum deformability, where both linear and circumferential arrangements of microfilaments reflect the lines of a tension field generated by the cell's contractile activity and spatially restricted by adhesions. Both the stress fibers and the circumferential rings of microfilaments are contracting isometrically. When grown on planar, rigid, basement membrane protein carpets, RPE cells are stimulated to spread and divide. In the absence of basic fibroblast growth factor (bFGF), the presumptive RPE cells acquire and maintain RPE markers with time in culture. In the presence of bFGF, the presumptive RPE loses the RPE markers, transdifferentiates into a pleomorphic neuroepithelium, and acquires a general neural marker such as the neural cell adhesion molecule.
TL;DR: Results indicate that rearrangement of the spatial positions of specific chromatin domains may depend upon transcriptional demands of the cell and may be taken to indicate the presence of a potential link between the positioning of specific gene sequences and cell function.
Abstract: Publisher Summary This chapter summarizes some of the evidence describing the three-dimensional (3-D) organization of interphase nuclei and correlates this evidence with results showing that the organization of interphase nuclei is dynamic and under the control of physiological stimuli. The considerable evidence indicates that specific chromatin domains in interphase nuclei of cells in vitro may move within the global confines of interphase nuclei. In addition, chromosome patterns in cells in vivo are dynamic, either during differentiation when cells exhibit stage-specific, characteristic patterns of centromeric satellite DNA or under conditions of altered functional states. Together, these results indicate that rearrangement of the spatial positions of specific chromatin domains may depend upon transcriptional demands of the cell and may be taken to indicate the presence of a potential link between the positioning of specific gene sequences and cell function. A body of evidence also indicates that rearrangement of chromosome patterns may occur in cells in vitro as well as in cells in vivo under pathological conditions. To ultimately assign a functional role to these phenomena, however, it would be necessary to show in intact cell assemblies that changes in the organization of chromatin domains within neuronal interphase nuclei may occur in response to physiological stimuli.
TL;DR: The idea is advanced that the evolution of the sheathed nuclear division contributed to the development of double spermatogenesis in Lepidoptera.
Abstract: Publisher Summary This chapter focuses on spindle architecture in Lepidoptera. The variability in spindle structure is illustrated by describing meiosis as well as mitosis in both sexes. Lepidoptera chromosomes are unusually small, and light microscopy has not contributed much to knowledge of chromosome structure in this group. Although observations are limited to a few species, fine structure studies suggest that Lepidoptera chromosomes represent a type intermediate between monokinetic and holokinetic chromosomes. Four different spindle types have been identified in Lepidoptera. These are somatic and gonial mitoses, female meiosis I, and divisions in eupyrene and apyrene spermatocytes. Though smaller, the spindles of spermatogonia and somatic tissues of Lepidoptera resemble those of mammalian cells. Meiosis I in female Lepidoptera is achiasmatic. Eupyrene spindles of Lepidoptera, which give rise to fertile spermatozoa, usually show a prominent spindle envelope and a rich intraspindle membrane system. Apyrene spindles, which produce sterile sperm, possess fewer membranes and microtubules (MTs) than the spindles of the “sheathed nuclear division.” Segregation of the chromatin is highly irregular in the apyrene line. The idea is advanced that the evolution of the sheathed nuclear division contributed to the development of double spermatogenesis in Lepidoptera. The acetylation status of MTs in mitotic and eupyrene meiotic spindles and its implications for MT behavior are described in the chapter.
TL;DR: This chapter discusses both lymphokines/interleukins and the hematopoietic growth factors (colonystimulating factors CSFs) only in connection with their role in the migration control of nonhematopOietic cells.
Abstract: Publisher Summary Cell migrations are at the basis of metazoan life. Starting with the migration of the sperm and ending with the invasive behavior of malignant tumor cells that finally kill their host, cell translocations over considerable distances are an essential part of the dynamics of higher eukaryotes. Much of information on cell migration has been obtained from in vitro studies with embryonic and tumor cells. Malignant tumors have provided “motile” and “immortalized” cells, and have also been the source of proteins that are initially isolated as “growth” (i.e., proliferation-stimulating) factors. The concept of angiogenesis as a crucial step in tumor development stimulated the search for and analysis of factors that modulate the proliferation and migration of endothelial cells. In addition to the polypeptides currently considered as bonafide or classic growth factors, the lymphokines (interleukins, cytokines), which are essential modulators of the immune system, also modulate cell migration. This chapter discusses both lymphokines/interleukins and the hematopoietic growth factors (colonystimulating factors CSFs) only in connection with their role in the migration control of nonhematopoietic cells.
TL;DR: This chapter presents the analysis of microfilament organization and contractile activities in the acellular slime mold Physarum polycephalum, which shows a common and permanent cytoskeletal differentiation in all investigated growth forms.
Abstract: Publisher Summary This chapter presents the analysis of microfilament organization and contractile activities in the acellular slime mold Physarum polycephalum. Physarum was predominantly used to analyze the morphology and contraction physiology of the cytoplasmic actomyosin system as exemplifying the situation in nonmuscle cells. During the vegetative phase, Physarum forms large motile phaneroplasmodia that can grow up to several square meters. Due to the large variety of the different life cycle and experimentally derived stages of Physarum, microfilaments can attain manifold manifestations ranging from a primitive actomyosin cortex beneath the plasma membrane in amoeboflagellates to an extremely complex arrangement of actomyosin fibrils extending through the entire cytoplasmic matrix in vegetative phaneroplasmodia. Most significant is the existence of the cortical microfilament system, which shows a common and permanent cytoskeletal differentiation in all investigated growth forms. The microfilament system serves two main functions. Together with the spectrin-like membrane skeleton, the actomyosin cortex stabilizes the cell surface and participates in morphogenetic events such as formation of an invagination system. The actomyosin cortex delivers motive force by regular contractile activities, which are transformed via the plasma membrane into hydraulic pressure gradients and finally result in protoplasmic streaming via gel-sol transformations.
TL;DR: The chapter begins with a description of different mechanisms of resistance, even though they may have been documented in only one of the classes of Resistance, and focuses on cellular resistance to cancer chemotherapy.
Abstract: Publisher Summary One of the most challenging aspects of cancer chemotherapy is the problem of resistance to clinical drugs. The reasons for clinical resistance may include pharmacokinetic or cell kinetic factors. It is generally accepted that cellular drug resistance is one of the major reasons that treatment fails. The mechanisms of resistance depend on several factors and circumstances that have given rise to the following classifications: (1) natural ( de novo or intrinsic) versus acquired resistance, (2) experimental versus clinical resistance, (3) resistance developed in rodent versus in human cell lines, (4) in vitro versus in vivo resistance and ( 5 ) low versus high degree of resistance. In addition, the dose schedule may affect resistance. Basically, cellular resistance depends on the biological possibilities which are available for a mammalian cell to escape cellular injury from a cytotoxic drug. Consequently, the mechanisms of resistance found in one cellular system may also occur in another. Considering drug resistance from this point of view, all mechanisms described may be relevant. The chapter begins with a description of different mechanisms of resistance, even though they may have been documented in only one of the classes of resistance, and focuses on cellular resistance to cancer chemotherapy.
TL;DR: The role of mechanical stimulation in the establishment and maintenance of muscle cell differentiation is discussed and the primitive myofibrils of the heart appear to be subject to the extrinsic tensile forces that must accompany these morphogenetic events.
Abstract: Publisher Summary This chapter discusses the role of mechanical stimulation in the establishment and maintenance of muscle cell differentiation. The striated tissues of the myocardium and axial skeleton are exquisitely sensitive to changes in mechanical load. In the heart, an acute increase in preload can act to augment cardiac output on a beat-to-beat time scale. In skeletal muscle, it serves to accelerate shortening velocity and increase contractile force. During early embryonic life, the developing cardiac myocyte displays a rounded, ovoid shape. Myofibrils are disseminated throughout the sarcoplasm and intercellular junctions are distributed at irregular intervals along the periphery of the cells. With continued development, the myocytes grow severalfold in size and begin to gradually elongate to assume a rod-like shape. The essential role which mechanical forces play in directing cardiac morphogenesis is readily apparent when an intact, developing heart is partially unloaded. Externally derived forces may also serve as an early signal that acts to direct the nucleation of myofibrils in the developing heart. Because the primitive myofibrils of the heart appear to be attached to the sarcolemma through nascent costameres and fascia adherens junctions, they appear to be subject to the extrinsic tensile forces that must accompany these morphogenetic events.
TL;DR: The characteristics of the permeant molecules that are most likely to have a major influence on nucleocytoplasmic exchanges relate to signal composition encoded in the primary structure of the protein; the accessibility of the signal to the receptors; and post-translational changes, which interfere with signal activity.
Abstract: Publisher Summary This chapter discusses the role of nuclear trafficking in regulating cellular activity The focus is on the specific and nonspecific mechanisms used by cells to regulate the nucleocytoplasmic distribution of proteins and RNA Regulation at this level could be achieved either by variations in the transport machinery or the properties of the permeant molecules Nuclear envelope separates the nucleoplasm from the remainder of the cell The envelope is a double membrane structure that contains the nuclear pores, circular spaces that are 70-80 nm in diameter, which are formed by the fusion of the inner and outer membranes The pores are not simply the openings that permit free communication between the nucleoplasm and cytoplasm, but contain highly organized supramolecular protein structures that regulate the movement of macromolecules The pores, along with their structural elements, are referred to as “pore complexes” Macromolecular exchanges through the pores can occur either by passive diffusion or signal-mediated transport The characteristics of the permeant molecules that are most likely to have a major influence on nucleocytoplasmic exchanges relate to signal composition encoded in the primary structure of the protein; the accessibility of the signal to the receptors, which could be affected by either binding reactions that anchor the permeant molecule to cytoplasmic elements or masking of the signal; and post-translational changes, such as phosphorylation, which interfere with signal activity
TL;DR: This chapter provides an overview of locomotion in tissue culture cells, with a positive correlation between adhesive strength, including in particular the formation of focal adhesions, and the abilities of different cell types to distort flexible substrata.
Abstract: Publisher Summary This chapter provides an overview of locomotion in tissue culture cells. To propel itself forward, a cell must somehow exert rearward forces on something in its immediate environment. In the case of tissue culture cells, this traction is exerted through adhesions to such substrata as glass, plastic, plasma clots, collagen fibers, or other materials. Traction can be detected by the distortions that it produces in culture substrata, as long as these are mechanically weak enough to be visibly distorted by traction; substrata that are used to study traction include plasma clots, collagen gels, silicone rubber membranes, pools of highly viscous silicone fluid, and other inert, insoluble, and viscous liquids. There is a positive correlation between adhesive strength, including in particular the formation of focal adhesions, and the abilities of different cell types to distort flexible substrata. Likewise there is a strong positive correlation with cytoskeletal organization; cells with well-developed stress fibers can be relied upon to exert strong traction, and drugs which disrupt cytoskeletal organization always weaken the traction.
TL;DR: This chapter describes the expression of butyrylcholinesterase (BChE) and acetylcholinease (A ChE) during avian neurogenesis, with particular emphasis on the recent studies, which reveal new functions for both BChE and AChE.
Abstract: Publisher Summary This chapter describes the expression of butyrylcholinesterase (BChE) and acetylcholinesterase (AChE) during avian neurogenesis, with particular emphasis on the recent studies, which reveal new functions for both BChE and AChE. The best-known member of the cholinesterase family is AChE, which degrades the neurotransmitter acetylcholine at the postsynaptic membrane of cholinergic synapses. BChE is enriched in the liver, heart, brain, and especially in serum. It is able to hydrolyze higher cholinesters as well as acetylcholine. The production of cholinesterases is developmentally regulated in a complex manner. The enzymes appear in different molecular forms in specific cell types and specific tissue parts. The entire history of embryonic cholinesterase development is divided into two main periods—namely, embryonic and synaptic. The first period consists of the early expression of cholinesterases, that is, during neurogenesis when cells of the neuroepithelium leave the mitotic cycle and start to differentiate. These cholinesterases are called “embryonic cholinesterases.” This early morphogeneti” period is distinguished from the synaptic period of cholinesterase expression, when neurofibrillar laminae and then synapses are established.