Showing papers on "Cellular differentiation published in 1968"

Differentiated Rat Glial Cell Strain in Tissue Culture

Abstract: Rat glial tumors, induced by injections of N-nitrosomethylurea, were plated and propagated in culture. Among a few cell strains obtained, one clone contains S-100 protein, which is unique to brain in vertebrates. Stationary-phase cultures contain approximately ten times more S-100 protein per cell than exponentially growing cells. When injected into newborn rats, cells producing S-100 grew as a glial tumor, which contained S-100 protein.

Embryonic development of the heart. I. A light and electron microscopic study of myocardial development in the early chick embryo

Abstract: Embryonic chick myocardium (stages 8+ to 12−) was studied by light and electron microscopy. The myocardium, which is initially comprised of radially oriented cells with large intercellular spaces gradually becomes more tightly packed. Intercellular spaces decrease and the cells assume a circumferential orientation. Myocardial cells remain epithelial throughout formation of the functional tubular heart and specialized epithelial junctions (apical junctional complex or terminal bars) undergo modification to form intercalated discs. Embryonic myocardial cells contain large amounts of free ribosomes and particulate glycogen, the latter often associated with portions of granular reticulum. Unlike developing skeletal muscle. The amount of granular reticulum contained in the myocardial cell cytoplasm is large and, along with a hypertrophied Golgi apparatus, suggests that these cells may have a secretory function. These organelles persist during the initial period of fibril formation. Myofibrils apparently form from non filamentous precursor material and not by alignment of sequentially synthesized components.

Chapter 6 Cell Aggregation and Differentiation in Dictyostelium

Abstract: Publisher Summary This chapter discusses experiments on the control of cell differentiation and pattern formation in a simple multicellular system. Aggregation patterns and mechanisms of Dictyostelium cells have been used as a model for these studies. The aggregation patterns are formed through self-organization; whereas the establishment of polarity in the conus is under the control of influences provided by exposure of a cell group to a liquid-air interphase. In the aggregation in D. minutum, pattern results from control of the number of cells that found aggregation centers, and also from the activity of a simple chemotactic system. In contrast, D. discoideum involves more complicated cell functions and interactions, particularly oscillation of the center's activity and transmission of stimuli. The chapter discusses how these phenomena in D. discoideum may be useful as models when pattern formation in other developmental systems is considered.

The cytoplasmic control of nuclear activity in animal development.

Abstract: Summary 1.This article reviews the occurrence, mechanism, and functional significance of the cytoplasmic regulation of nuclear activity during cell differentiation and especially during early animal development. 2.Nuclei from brain, and from other kinds of adult cell normally inactive in DNA synthesis, are rapidly induced to commence DNA synthesis by components or properties of intact egg cytoplasm. The components of egg cytoplasm which induce DNA synthesis are not species-specific and they are likely to include DNA polymerase. It is known that DNA polymerase exists in egg cytoplasm before it becomes associated with nuclei in which it is effective. The induction of DNA synthesis in brain nuclei by living egg cytoplasm is always preceded by a pronounced nuclear swelling, a dispersion of chromosomes or chromatin, and the entry of cytoplasmic protein into the nucleus. 3.RNA synthesis can be experimentally induced or repressed by living cytoplasm. The cytoplasm of unfertilized and fertilized eggs appears to contain components which can reversibly and independently repress the synthesis of ribosomal RNA, transfer RNA, and heterogeneous RNA. RNA synthesis can be induced by introducing nuclei inactive in this respect into the cytoplasm of cells very active in RNA synthesis. The induction and repression of RNA synthesis is preceded by a marked swelling of the nucleus and the dispersion of its chromosome material. 4.The cytoplasmic control of chromosome condensation before division has been demonstrated by introducing sperm or adult brain nuclei into the cytoplasm of oocytes undergoing meiotic maturation. 5.The evidence that regional differences in the composition of eggs and other cells are associated with changes in nuclear and gene activity is reviewed in Section 111. While it is certain that these regional differences are of great importance in cell differentiation, evidence that they have a direct effect on nuclear activity has been obtained in a few instances only. In some species it has been shown that the cytoplasmic components related to germ-cell differentiation include RNA and, frequently, granules. 6.It is concluded that whenever nuclei are introduced experimentally into the cytoplasm of another cell, they very quickly assume, in nearly every respect, the nuclear activity characteristic of the host cell. In many instances, altered function has been demonstrated in nuclei which subsequently support normal development. The induced nuclear changes are therefore regarded as normal and it is believed that they are achieved through the same mechanism as that by which the host cell nucleus originally came to function in its characteristic way. Examples are cited to show that changes in gene activity very frequently arise immediately after mitosis. The changes induced experimentally in transplanted nuclei resemble in very many respects those undergone by nuclei which are naturally reconstituted after mitosis, and it is argued that the two processes are functionally equivalent, It is suggested that during telophase of mitosis, chromosomes are reprogrammed in respect of potential gene activity by association with cytoplasmic proteins. Inter-phase nuclei seem not to show changes of gene activity except when they undergo a pronounced enlargement after entering a new cytoplasmic environment.

An electron microscopic study of the neuroglia during postnatal development of the rat cerebrum.

Abstract: The differentiation of spongioblasts from undifferentiated cells and into neuroglial cells has been studied in the postnatal rat cerebral cortex with the electron microscope. The nuclei of all the non-neural elements are characterized by clumping of dense chromatin, especially near the nuclear envelope. The undifferentiated cells possess only a thin rim of perinuclear cytoplasm containing few organelles. Spongioblasts are characterized by an increased number of cytoplasmic organelles, mostly mitochondria and Golgi complex, and by the growth of processes. These cells mature and take on either the features of oligodendrocytes or astrocytes. The multiple oligodendrocyte processes are thin and branching and develop intimate contacts with the developing axons. Early stages of myelination are characterized by the envelopment of axons by oligodendrocyte processes which overlap each other to form inner and outer tongues that are cheracteristic of central nervous system myelin. Astrocytes can be distinguished by the presence of cytoplasmic glycogen particles and fibrils. Processes of these latter cells develop intimate relations with the developing blood vessels. A variety of cell was occasionally encountered which is termed the polycystic cell. This cell may be quite large, contains numerous cysts and vesicles of various types and appears to be a form of spongioblast. No cells which would qualify as “microglia” were observed.

The development of the female Drosophila reproductive system.

Abstract: Light and electron microscopical studies allow a descriptive account to be given of the preadult development of the ovary of Drosophila melanogaster. The lineage of the cell groups which contribute to the tissues of the adult ovary has been determined. The earliest morphologically detectable event in the differeentiation of each ovariole is the formation during the larval period of its terminal filament. Oogonia play no role in the induction of terminal filaments. The developmental events which transform a spherical mass of ovarian cells into a collection of multicellular cylinders is described. The importance in morphogenesis of acellular membranes secreted at the interface separting cells of different prospective significances is stressed. Such membranes may serve to regulate the future migration of cell populations or as sites of attachment for monolayers of cells which later fuse to form multinucleated muscle sheaths. The transformation of oogonia to cystoblasts coincides with and presumably depends upon the same hormonal stimulus which causes metamorphosis. The first oocytes to undergo crossing over do so between 24 and 36 hours after puparium formation.

Intercellular bridges and synchronization of germ cell differentiation during oogenesis in the rabbit

Abstract: A certain degree of synchronization of germ cell differentiation is a general feature of mammalian oogenesis. In the rat (3, 10), mouse (4), and rabbit (15, 16), germ cell differentiation is highly synchronized in that there is a direct correspondence between fetal age and predominant stage of cellular activity. In the guinea pig (11), monkey (2), and man (1), the synchronized pattern is less apparent because of a considerable overlapping of mitosis, meiosis, and degeneration. Correpondence between age and stage of differentiation of a significant percentage of germ cells is found even in these species, however. In the course of an electron microscopic study of ovarian development in the newborn rabbit, we have observed that the synchronization of the oogenetic process finds expression not only in the close relationship between fetal age and stage of cellular differentiation, but also in the maturation of the germ cells in groups and in the synchronous differentiation of all the cells in each group. Such synchronization appears to be related

Heart induction in salamanders.

Abstract: Heart determination is a gradual, cumulative process involving inductive and suppressive interactions between the heart mesoderm and nearby embryonic tissues. Our analysis of heart determination in the California newt, Taricha torosa, includes defect and other in vivo experiments, and explants in epidermal vesicles and into hanging drops. Explants of presumptive heart mesoderm from neurulae into hanging drops of a completely defined salt solution (Niu-Twitty solution) produce beating hearts only infrequently. The addition of various other tissues and fractions of tissue homogenates changes the frequency and the rate of differentiation. These two parameters were used to assess the stimulatory and suppressive effects of tissues and tissue fractions on the differentiation of the presumptive heart mesoderm. At least three different factors are active in eliciting and regulating heart differentiation. A specific heart inductor in anterior endoderm increases the rate and the freqency of heart differentiation. A general stimulatory factor in epidermis and other embryonic tissues increases the frequency, but not the rate, of heart differentiation. An inhibitory agent in cranial fold and neural plate tissues delays or prevents heart differentiation. These three factors operate from intact tissues in the embryo or when explanted in vesicles or hanging drops, and are effectively present in a fraction (from sephadex column chromatography) of homogenates of the appropriate tissues.

Possible mechanism for Mycoplasma inhibition of lymphocyte transformation induced by phytohaemagglutinin.

Abstract: Mycoplasma pneumoniae stimulates transformation and mitosis in cultures of lymphocytes obtained from sensitized individuals1, as do other antigens2. In contrast, M. hominis3 and M. arthritidis4 inhibit lymphocyte transformation induced by phytohaemagglutinin (PHA). We have examined the effects of different species of Mycoplasma on lymphocyte cultures in an attempt to elucidate the mechanism of mycoplasma inhibition of PHA-induced transformation.

Function of the lactate dehydrogenase B gene in mouse erythrocytes: evidence for control by a regulatory gene.

Abstract: Experimental evidence suggests that cells comprising complex multicellular organisms possess qualitatively equivalent ensembles of genes, but the differentiation of these cells requires differential gene expression. According to this hypothesis, differentiation occurs primarily as the result of a patterned activation of certain genes and a repression of others. Developmental control of gene expression can operate at many levels, such as transcription, translation, end product alteration, or combinations of these. It is reasonable to expect that the control processes should themselves be genetically controlled and, as a result, that mutations affecting control should also occur. Evidence for mutations affecting certain levels of control in higher organisms exists in fungi, Drosophila, plants, and mammals.'-3 These examples provide some insight into the mechanisms controlling differential gene expression. In this report we present genetic evidence for a mammalian gene that appears to control the expression of an independent structural gene in a differentiated cell. This gene controls the appearance of the active B subunit, but not the A subunit, of the lactate dehydrogenase (LDH) tetramer in mouse erythrocytes. It has no detectable effect in any other tissue examined. Preliminary evidence has been reported elsewhere.4 Lactate dehydrogeniase (EC 1.1.1.27) is composed of two electrophoretically distinct subunits, A and B, which associate at random to form five tetrameric isozymes, each with a molecular weight of about 135,000.5, 6 The five isozymes are generated by assortment of the A and B subunits into all possible combinations of four.7 Formulas for the five isozymes may be written as follows: BBBB = LDH-1; BBBA = LDH-2; BBAA = LDH-3; BAAA = LDH-4; AAAA = LDH-5. These five forms are the principal lactate dehydrogenase isozymes found ubiquitously in mammals. A high degree of tissue specificity characterizes isozyme patterns. Certain tissues contain more LDH-5 than LDH-1, thus demonstrating that unequal amounts of the A and B subunits are available for tetrameric association. Differential expression of the LDH isozymes has also been shown during specific tissue development.8 The developmental specificity of such tissue indicates that control mechanisms exist for regulating the relative amounts of synthesis of the A and B subunits of LDH. In the present study two lactate dehydrogenase phenotypes were observed in mouse erythrocytes but not in other tissues. In one phenotype, LDH B subunits were expressed, while in the second, LDH B subunits were absent. This phenotypic difference was iniherited according to expectations of two alleles at an autosomal locus. The allele that specifies the formation of LIDH B subunits is dominant to that which is associated with the absence of these subunits.

Kinetics of gas diffusion in mammalian cell culture systems. II. Theory

Abstract: Mathematical models have been constructed which relate the depth of the culture fluid overlay to the oxygen available to mammalian cells cultured under static conditions. These models suggest that the maintenance of a given rate of oxygen utilization by some culture systems may be critically depended on this fluid depth and on the solubility and rate of diffusion of oxygen in the culture fluid. The importance of these concepts as applied to the isolation and growth of differentiated cells representative of the tissue of origin are noted.

Cellular differentiation of the immune system of mice. I. Separate splenic antigen-sensitive units for different types of anti-sheep antibody-forming cells.

Abstract: Spleen cell suspensions of unprimed donor mice containing precursors of immunocytes have been transplanted into X-irradiated recipient mice. In the presence of antigen (sheep erythrocytes) these precursors, called antigen-sensitive units, gave rise to progeny cells secreting specific antibody. We studied quantitatively the production of cells releasing IgM hemolysins (direct plaque-forming cells), IgG hemolysins (indirect plaque-forming cells), and hemagglutinins (cluster-forming cells). We found that each of these immunocyte populations was distinct, i.e., that cells releasing agglutinins did not, as a rule, release hemolysins, and vice versa. We also found that cell populations secreting IgM hemolysins did not shift, under certain experimental conditions, to the production of IgG hemolysins during the primary immune response. By transplanting graded numbers of spleen cells, we succeeded in limiting to one or a few the number of antigen-sensitive units that reached the recipient spleen. We estimated thereby the frequency of antigen-sensitive units in donor cell suspensions and tested their potential for production of immunocytes of more than one type. Our results indicated that antigen-sensitive units were unipotent for they displayed in the spleens of unprimed donors the same restrictions of function and heterogeneity (antibody-specificity differentiation, antibody-class differentiation) found among antibody-forming cells. Furthermore, antigen-sensitive precursors for direct plaque-forming cells, indirect plaque-forming cells, and cluster-forming cells were detected in the spleens of unprimed mice in different frequencies, i.e., 1 in approximately 10(6), 1 in approximately 7 x 10(6), and 1 in approximately 19 x 10(6) spleen cells, respectively. We concluded that relatively advanced differentiation of potentially competent cells occurs before sheep erythrocyte administration. The relevance of this finding for the broad spectrum of immunologic reactivities and for the heterogeneity of antibody responses to given antigens was discussed.

Regulation of melanin synthesis in mammalian cells, as studied by somatic hybridization. I. Evidence for negative control.

Abstract: Somatic hybrids between pigmented Syrian hamster cells and unpigmented mouse cells were isolated and propagated in vitro. These hybrids are unpigmented and lack dopa oxidase (and tyrosinase) activity, which is correlated with the pigmentation of the Syrian hamster cells. In contrast, the presence of three other enzymes (LDH, MDH, and thymidine kinase) also specified by the hamster genome but unrelated to pigment synthesis is observed in the hybrid cells. This suggests that the repression of dopa oxidase in these cells is a specific effect on the enzyme associated with the differentiated state of pigment cells. It is concluded that the genetic control of differentiation in this case involves a diffusible regulator substance which functions negatively.

The Stability of the Determined State in Cultures of Imaginal Disks in Drosophila

Abstract: The development of different cell types in higher organisms, arising from one cell type (the zygote), is designated as cell differentiation. Differentiation is initiated by the process of determination which programs the cells for their future developmental pathway. There is accumulating evidence that the developmental programs reside in the genome and represent sets of genes acting in a coordinate fashion. The fundamental problem of how different genes are coordinately controlled remains to be elucidated. Two major categories of determinative processes are known: one is embryonic induction which involves cell or tissue interactions by means of diffusible inducing substances, and another is cytoplasmic segregation which is based upon factors intrinsic to the differentiating cells. In the latter case differentiation may be achieved by unequal distribution during cell division of cell components acting as determinative factors. Since determination creates the first essential differences among cells, an understanding of this process might be a key to the problem of differentiation in general. One approach to elucidate determination is to isolate the inducing substances produced by the inducer tissue and to study their action on the reacting tissue. Another approach, which will be considered in this chapter, is to study determination in “mosaic systems” in which intrinsic factors are responsible for setting up the developmental program.

Cellular differentiation and the aging process in cartilaginous tissues. Mucopolysaccharide synthesis in cell cultures of chondrocytes.

Abstract: Primary cell cultures of differentiated chondrocytes were shown to produce chondroitin-4-sulfate as the predominant mucopolysaccharide, with suggestive evidence for the synthesis of keratan sulfate and possibly chondroitin-6-sulfate. Chicken embryonic cartilage was shown to be composed mainly of chondroitin-4-sulfate, with a small amount of chondroitin-6-sulfate, but essentially no keratan sulfate. These findings were compared to the data of others, and a hypothesis explaining the aging process in cartilage in terms of cellular differentiation was presented.

Modification in transfer RNA during the differentiation of wheat seedlings

Abstract: Mechanisms involved in the regulation of the synthesis of macromolecules have been investigated primarily in bacterial systems. Various schemes have been proposed which implicate transcription of the genetic message as the initial site for the regulation of enzyme synthesis. Recently, attention has been focused on the steps involved in translation of the ribonucleic acid message as the level at which regulation occurs. It has been suggested that certain transfer RNA molecules are involved in the regulation of cell metabolism and cell differentiation at the translation level.\" 2 If such conjecture were true, one should find evidence of changing tRNA populations when the physiologic processes of an organism are profoundly altered. Changes in the distribution of certain tRNA species have been reported in bacterial cells undergoing sporulation,3 4 in phageinfected bacteria, 5. 6and in virus-infected animal cells.7 IA the present investigation we have examined the aminoacylated-tRNA's of wheat embryos and wheat seedlings. The purpose was to learn whether or not detectable changes occur in the distribution of tRNA's during differentiation. In this report we show changes in at least three aminoacyl-tRNA's and discuss their possible role in differentiation. Materials and Methods.-The organism studied was Triticum aestivum (var. Pawnee). Pawnee wheat seed was obtained from the Champaign (Illinois) County Seed Co. Radioactivity was determined by liquid scintillation spectroscopy on 1.5to 2-ml fractions in Bray's dioxane fluid. The samples were cooled 8 hr before they were counted. Seeds were germinated in trays on paper towels saturated with water containing 100 ,g dihydrostreptomycin sulfate per milliliter. The trays were covered with plastic film (Saran Wrap) and left at room temperature in room lighting. Nongerminated embryos were isolated by the method of Johnston and Stern.8 The partial purification of aminoacyl-tRNA synthetases from wheat embryos, the isolation of wheat embryo and wheat seedling sRNA, and the characterization of the in titro aminoacylation of wheat tRNA will be reported elsewhere.'0 The methylated albumin kieselguhr column of Mandel and Hershey9 was used throughout. Soluble RNA samples from embryos (0 hr) and seedlings (48 hr) were separately charged in vitro with a given C14 or H3 amino acid. The reaction mixture contained a C14 amino acid (sp. act. of 50 mc/mmole) or a H3 amino acid (sp. act. between 0.25 and 4.8 c/mmole) at a concentration of at least 10-6 mmoles amino acid/reaction; 250 or 500 ,ug sRNA; 0.1-2.0 mg protein (amino-acyl-RNA synthetase fraction); 50 Mmoles Tris, pH 8.0 at 18'C; 5 Mmoles MgCl2; 5,pmoles adenosine 5'-triphosphate (ATP); 1 Mmole reduced glutathione; 0.15 Mmole cytidine 5'-triphosphate (CTP); and glass-distilled water to a total volume of 0.5 ml. The reaction mixture was incubated at 18'C until a level of saturation was reached. Results.-(a) Cochromatography of individual species of tRNA's from embryos and 48-hour seedlings: Radioactivity and optical density profiles for embryo and seedling aminoacyl-tRNA coeluted from MAK are given in Figure lA-H. Profiles for valyl-, lysyland prolyl-tRNA are shown in Figures 2, 3A, and.4A.

Hormone-dependent differentiation of mammary gland in vitro.

Abstract: Publisher Summary This chapter discusses the studies of the synthesis of specific protein markers of differentiated function in an attempt to define stages of transition in the differentiation of mammary alveolar cells in vitro. These studies have provided information relating to several major questions regarding the nature of differentiation of mammalian cells. Evidence has been provided to support the concept that cell division is a prerequisite for the expression of new differentiated function. The agent of primary importance in effecting covert differentiation, hydrocortisone, acts upon the parent cells, and new function is expressed by the daughter cells. However, the requirement for cell division and the basis for the new genetic expression remain to be explained in molecular terms. Concern with the intracellular control mechanisms involved must be coupled with recognition of the possible importance of mesenchymal cells in modifying the response of epithelial cells. These studies have emphasized the vulnerability of proliferating cells to factors in the environment, especially to hormonal agents that have the capacity to alter genetic expression within cells.

Cell affinities in antennal homoeotic mutants of drosophila melanogaster

Abstract: DISSOCIATED embryonic cells show, in culture, cell affinities and morphogenetic movements which are tissue characteristic. While cells which derive from the same organ and tissue are able to reconstitute the original cell arrangements in mosaic fashion, cells from different organs sort out and regroup separately. This situation holds for vertebrate cells as well as for cells of many other lower organisms (see TRINKAUS 1966 for discussion). In Drosophila the adult cuticle consists of several cell structures specifically arranged into segment characteristic patterns. The adult cuticular structures are formed from cells of the imaginal discs of the larvae which undergo differentiation during metamorphosis. A variety of mutants in Drosophila meLanogaster change the color or form of single cuticular structures (cell mutants). With the aid of cell marker mutants HAWRN, ANDERS and URSPRUNG (1959) have shown that dissociated cells of the same imaginal disc are able to reaggregate and reconstruct the adult patterns of this disc integrated in mosaic fashion. However, dissociated cells deriving from different imaginal discs (NOTHIGER 1964; GARCIA-BELLIDO 1’36613) or from different regions of the same disc (GARCIABELLIW 1966a) sort out or segregate in aggregates. Furthermore, cells from homologous imaginal discs (different leg discs) reconstruct the common patterns in a typical mosaic integration; whereas they segregate when they correspond to different patterns (GARCIA-BELLIDO 1966a). These results are indicative of a highly specific cell determination correlated with highly selective cell affinities in the dissociated cells of the imaginal discs. When cultured in u h o , aggregated cells may change their prospective differentiation into that typical for other imaginal discs. The underlying phenomenon is called transdetermination and is assumed to be based upon a non-mutational change in the activity of sets of genes (HADORN 1966). When studied in cell aggregates, the transdetermined cells show new cell affinities which correspond to their new cell determination ( GARCIA-BELLIDO 1966b). The hypothesis was advanced then that the same specific genes are responsible for both the selective affinity and the correlative differentiation of the imaginal disc cells. There are mutants in Drosophila which specifically change the arrangement of the differentiated structures in the adult cuticle. Such mutants can be con-

A study of the interdependence of red cell and bone marrow stem cell populations.

Abstract: Haemolytic anaemia was produced in rabbits by the administration of a regular course of incompatible red cell iso-antibody. A greatly increased rate of red cell production was observed but haemoglobin and reticulocyte counts exhibited vigorous and continuing fluctuations with, in the adult rabbits, a regular periodicity. The effects of steroids and splenectomy on this antibody-mediated red cell destruction were found to be virtually unobservable, and the implications of this with regard to the haemolytic anaemias of man resulting from red cell destruction by iso- or auto-antibodies are discussed. The significance of the fairly regular oscillations was analysed on the basis of evidence on the various parts of the haemopoietic system. The nature of these and other oscillations observed led to the suggestion that they could be understood in terms of interactions of a four-component system: the stem cell population; a stem cell specific mitotic inhibitor, termed chalone, which is produced in proportion to the stem cell population and catabolized in proportion to its own level; the differentiated cell population; and erythropoietin. The features of the various oscillations in terms of the four-component system, and the effects of the parameters on these features, are discussed.

Morphological cell death in the post-embryonic development of the insect optic lobes.

Abstract: THE incidence of cell death among differentiating cells of the embryonic vertebrate central nervous system is well documented1–3, and there is evidence that in some cases its occurrence is influenced by the peripheral load encountered by the outgrowing fibres1–5. In vertebrate neural ontogeny both morphogenetic and histogenetic cell death have been observed6,7. Histogenetic cell death—which is involved in the differentiation of organs and tissues—has also been reported in the embryonic nervous systems of insects, for example, Tenebrio8 and the gall midge, Miastor (personal communication from S. Counce). It is reported here in the post-embryonically developing optic lobes of the larval and pupal brains of the endopterygote Danaus plexippus L. (Lept.) and is of special interest because it is possible to determine the age of a particular cell in this region and to observe cell and fibre areas of a wide range of ages within the same individual (our unpublished results).