Showing papers on "Cellular differentiation published in 1985"

The in vitro development of blastocyst-derived embryonic stem cell lines: formation of visceral yolk sac, blood islands and myocardium

Abstract: The in vitro developmental potential of mouse blastocyst-derived embryonic stem cell lines has been investigated. From 3 to 8 days of suspension culture the cells form complex embryoid bodies with endoderm, basal lamina, mesoderm and ectoderm. Many are morphologically similar to embryos of the 6- to 8-day egg-cylinder stage. From 8 to 10 days of culture about half of the embryoid bodies expand into large cystic structures containing alphafoetoprotein and transferrin, thus being analagous to the visceral yolk sac of the postimplantation embryo. Approximately one third of the cystic embryoid bodies develop myocardium and when cultured in the presence of human cord serum, 30% develop blood islands, thereby exhibiting a high level of organized development at a very high frequency. Furthermore, most embryonic stem cell lines observed exhibit similar characteristics. The in vitro developmental potential of embryonic stem cell lines and the consistency with which the cells express this potential are presented as aspects which open up new approaches to the investigation of embryogenesis.

Soluble interleukin 2 receptors are released from activated human lymphoid cells in vitro.

Abstract: With the use of an enzyme-linked immunoabsorbent assay to measure soluble human interleukin 2 receptors (IL 2R), certain human T cell leukemia virus I (HTLV I)-positive T cell lines were found to spontaneously release large quantities of IL 2R into culture supernatants This was not found with HTLV I-negative and IL 2 independent T cell lines, and only one of seven B cell-derived lines examined produced small amounts of IL 2R In addition to this constitutive production of soluble IL 2R by certain cell lines, normal human peripheral blood mononuclear cells (PBMC) could be induced to release soluble IL 2R by plant lectins, the murine monoclonal antibody OKT3, tetanus toxoid, and allogeneic cells Such activated cells also expressed cellular IL 2R measurable in detergent solubilized cell extracts The generation of cellular and supernatant IL 2R was: dependent on cellular activation, rapid, radioresistant (3000 rad), and inhibited by cycloheximide treatment NaDodSO4-polyacrylamide gel electrophoresis analysis of soluble IL 2R released from either the HTLV I-positive T cell line HUT 102B2 or normal phytohemagglutinin-activated PBMC demonstrated molecules of apparent Mr = 35,000 to 40,000, and 45,000 to 50,000, respectively, somewhat smaller than the mature surface receptor on these cells The release of soluble IL 2R appears to be a characteristic marker of T lymphocyte activation and might serve an immunoregulatory function during both normal and abnormal cell growth and differentiation

Production of transgenic rabbits, sheep and pigs by microinjection

Abstract: Direct microinjection has been used to introduce foreign DNA into a number of terminally differentiated cell types as well as embryos of several species including sea urchin, Candida elegans, Xenopus, Drosophila and mice. Various genes have been successfully introduced into mice including constructs consisting of the mouse metallothionein-I (MT) promoter/regulator region fused to either the rat or human growth hormone (hGH) structural genes. Transgenic mice harbouring such genes commonly exhibit high, metal-inducible levels of the fusion messenger RNA in several organs, substantial quantities of the foreign growth hormone in serum and enhanced growth. In addition, the gene is stably incorporated into the germ line, making the phenotype heritable. Because of the scientific importance and potential economic value of transgenic livestock containing foreign genes, we initiated studies on large animals by microinjecting the fusion gene, MT-hGH, into the pronuclei or nuclei of eggs from superovulated rabbits, sheep and pigs. We report here integration of the gene in all three species and expression of the gene in transgenic rabbits and pigs.

Cell differentiation in the retina of the mouse

Abstract: Cell differentiation in the retina of the mouse during the postnatal period was studied by autoradiography. Animals were injected with 3H-thymidine at ages extending from the day of birth through postnatal day 11. Six weeks later the distribution of labeled nuclei in the cells of the mature neural retina was analyzed to determine when these cells completed their final mitosis prior to differentiating. Central and peripheral zones were analyzed separately. Cell division ceases by 5–6 days in the center of the retina and by 11 days in the periphery. Among cells produced postnatally, 73% differentiate as rods, 20% as bipolar cells, 6% as Muller cells, and 1% as amacrine and ganglion cells. At all stages of embryogenesis, the differentiation of at least three and as many as six distinct types of specialized cells is initiated simultaneously within the ventricular cell population.

Insulin-like growth factors as intraovarian regulators of granulosa cell growth and function.

Abstract: A relatively large body of evidence now appears to support the existence of the essential ingredients for novel intraovarian IGF-driven control mechanisms. Indeed, evidence presented in this communication is in keeping with the possibility that the granulosa cell may be the site of IGF production, reception, and action. Although the relevance of IGFs to ovarian cell types other than the granulosa cell is largely unknown, one cannot at the present time exclude the possibility of nongranulosa cell contributions to intraovarian IGF production, reception, and action. Indeed, preliminary affinity cross-linking studies (Adashi, Resnick, Svoboda, Van Wyk and D'Ercole; unpublished data) suggest the existence of type-I and type-II receptors in nongranulosa cell compartments. The above notwithstanding, IGFs of granulosa (and possibly circulatory) origins may interact with granulosa cell autoreceptors either independently or in synergy with other granulosa cell agonists. According to this view, IGFs may act in the autocrine mode to stimulate granulosa cell replication on the one hand and promote granulosa cell differentiation on the other. Although proliferation and terminal differentiation may prove mutually exclusive under some circumstances, coexistence of the two processes is being increasingly recognized. In this context, some studies of porcine granulosa cells support a dual role for IGFs in granulosa cell ontogeny. As such, the IGFs can be added to a growing list of growth factors known to modulate granulosa cell growth and function, including EGF, PDGF, and FGF. Our findings indicate that Sm-C/IGF-I synergizes with FSH in the induction of rat granulosa cell aromatase activity at nanomolar concentrations compatible with its granulosa cell receptor binding affinity (thus far studied only in porcine cells. A role for Sm-C/IGF-I in the regulation of this key granulosa cell function would be in keeping with the possibility that Sm-C/IGF-I may partake in the assertion and maintenance of dominance by the selected follicle(s) or in promoting juvenile and early follicular development. Moreover, the ability of Sm-C/IGF-I to potentiate this and other FSH-driven ovarian functions may also account, at least in part, for the puberty-promoting effect of growth hormone. This permissive action of growth hormone has been initially suggested by observation in growth hormone-deficient rats, mice (dwarf mutants, and humans (sporadic, hereditary or acquired growth hormone deficiency.(ABSTRACT TRUNCATED AT 400 WORDS)

Plasticity of the differentiated state.

Abstract: Heterokaryons provide a model system in which to examine how tissue-specific phenotypes arise and are maintained. When muscle cells are fused with nonmuscle cells, muscle gene expression is activated in the nonmuscle cell type. Gene expression was studied either at a single cell level with monoclonal antibodies or in mass cultures at a biochemical and molecular level. In all of the nonmuscle cell types tested, including representatives of different embryonic lineages, phenotypes, and developmental stages, muscle gene expression was induced. Differences among cell types in the kinetics, frequency, and gene dosage requirements for gene expression provide clues to the underlying regulatory mechanisms. These results show that the expression of genes in the nuclei of differentiated cells is remarkably plastic and susceptible to modulation by the cytoplasm. The isolation of the genes encoding the tissue-specific trans-acting regulators responsible for muscle gene activation should now be possible.

Identification of major cell classes in the developing mammalian nervous system

Abstract: A major difficulty in studying early developmental processes and testing hypotheses of possible cellular mechanisms of development has been the inability to reproducibly identify specific cell types. We have generated monoclonal antibodies that distinguish among major cell types present during mammalian neurogenesis. These antibodies have been used to analyze the development of cellular organization in the early nervous system. Monoclonal antibody Rat-401 identifies a transient radial glial cell in the embryonic rat central nervous system (CNS) that is temporally and spatially suited to guide neuronal migration. Rat-401 also identifies a peripheral non-neuronal cell that may establish axon routes from the CNS to the periphery. Monoclonal antibody Rat-202 recognizes an antigen present in early axons, their growth cones, and filopodia, and has allowed us to follow early axons and observe the structures they contact. Two other antibodies that recognize axons demonstrate antigenically distinct phases in axon development. In addition, we report a marker for another cell class present in the developing nervous system, the endothelial cells that give rise to the CNS vasculature.

The action of oncogenes in the cytoplasm and nucleus

Abstract: As many as 40 distinct oncogenes of viral and cellular origin have been identified to date Many of these genes can be grouped into functional classes on the basis of their effects on cellular phenotype These groupings suggest a small number of mechanisms of action of the oncogene-encoded proteins Some data suggest that, in the cytoplasm, these proteins may regulate levels of critical second messenger molecules; in the nucleus, these proteins may modulate the activity of the cell's transcriptional machinery Many of the gene products can also be related to a signaling pathway that determines the cell's response to growth-stimulating factors Because some of these genes are expressed in nongrowing, differentiated cells, the encoded proteins may in certain tissues mediate functions that are unrelated to cellular growth control

Human leukemic models of myelomonocytic development: a review of the HL-60 and U937 cell lines.

Abstract: The human leukemic myeloblast HL-60 and monoblast U937 cell lines have made important contributions to the disciplines of cancer, hematology, and immunology. As sources of leukemic cells, they have been used for the study of neoplasia and therapeutics. As sources of hemic cells, they have been used for biochemical and biological analysis of regulation and differentiation in myelopoiesis. When stimulated with immunomodulatory factors, the cell lines develop properties of host-defense effector cells. They are also a source of cytokines that affect other cell types.

Decreased expression of N- myc precedes retinoic acid-induced morphological differentiation of human neuroblastoma

Abstract: Proto-oncogenes may be important in the cellular processes central for the growth and differentiation of normal cells. N-myc is a DNA sequence which shares limited homology to the proto-oncogene c-myc and has been found to be amplified in both primary tissue and cell lines from neuroblastoma, a childhood tumour of neuroectodermal origin. Differentiation of this embryonal tumour is of clinical importance, since occasional tumours have been noted to differentiate in vivo to benign ganglioneuroma. In vitro, many human neuroblastoma cell lines can be induced to differentiate morphologically and biochemically by a variety of agents. Retinoic acid (RA), an analogue of vitamin A, has been shown to inhibit neuroblastoma cell growth and clonability in soft agar, and to induce extensive neurite outgrowth. Therefore we examined the relationship of N-myc expression to the in vitro differentiation of these cells. We report here that in the case of RA-induced differentiation, a decreased level of expression is detected within 6 h of treatment and precedes both cell-cycle changes and morphological differentiation.

Expression of interleukin-2 receptors as a differentiation marker on intrathymic stem cells.

Abstract: The thymus is regarded as the primary site for T-cell lymphopoiesis, but very little is known about the lineage inter-relationships of cells within that organ. At least four subpopulations of mouse thymocytes can be defined on the basis of staining with monoclonal antibodies directed against the T-cell differentiation antigens Lyt-2 and L3T4 (ref. 2). Thus immunocompetent (medullary) thymocytes, like peripheral T cells, express either Lyt-2 (cytotoxic phenotype) or L3T4 (helper phenotype) but not both, whereas non-functional (cortical) thymocytes express both markers. In addition, a small subpopulation comprising 2-3% of cells in the thymus and expressing neither Lyt-2 nor L3T4 has recently been described. The latter cells have the properties of intrathymic 'stem cells' in that they are the first to appear in the embryonic thymus and at least some can be shown to give rise, both in vivo (ref. 4. and our unpublished data) and in vitro, to other thymocyte subpopulations. We show here that 50% of Lyt-2-/L3T4- cells in the adult thymus express receptors for the polypeptide growth hormone interleukin-2 (IL-2) whereas other cells in the thymus do not. Furthermore, immunohistochemical localization studies on frozen sections indicate a disperse distribution of IL-2 receptor-positive cells in both the cortex and medulla. These novel findings have potential implications in the context of current models of differentiation pathways within the thymus.

Extracellular matrix regulates Sertoli cell differentiation, testicular cord formation, and germ cell development in vitro.

Abstract: Sertoli cell preparations isolated from 10-day-old rats were cultured on three different substrates: plastic, a matrix deposited by co-culture of Sertoli and peritubular myoid cells, and a reconstituted basement membrane gel from the EHS tumor. When grown on plastic, Sertoli cells formed a squamous monolayer that did not retain contaminating germ cells. Grown on the matrix deposited by Sertoli-myoid cell co-cultures, Sertoli cells were more cuboidal and supported some germ cells but did not allow them to differentiate. After 3 wk however, the Sertoli cells flattened to resemble those grown on plastic. In contrast, the Sertoli cells grown on top of the reconstituted basement membrane formed polarized monolayers virtually identical to Sertoli cells in vivo. They were columnar with an elaborate cytoskeleton. In addition, they had characteristic basally located tight junctions and maintained germ cells for at least 5 wk in the basal aspect of the monolayer. However, germ cells did not differentiate. Total protein, androgen binding protein, transferrin, and type I collagen secretion were markedly greater when Sertoli cells were grown on the extracellular matrices than when they were grown on plastic. When Sertoli cells were cultured within rather than on top of reconstituted basement membrane gels they reorganized into cords. After one week, tight junctional complexes formed between adjacent Sertoli cells, functionally compartmentalizing the cords into central (adluminal) and peripheral (basal) compartments. Germ cells within the cords continued to differentiate. Thus, Sertoli cells cultured on top of extracellular matrix components assume a phenotype and morphology more characteristic of the in vivo, differentiated cells. Growing Sertoli cells within reconstituted basement membrane gels induces a morphogenesis of the cells into cords, which closely resemble the organ from which the cells were dissociated and which provide an environment permissive for germ cell differentiation.

A Macrophage Factor Inhibits Adipocyte Gene Expression: An in Vitro Model of Cachexia

Abstract: Certain infections and malignancies in mammals cause the development of a condition known as cachexia in which the animal continues to lose weight, often while consuming an adequate diet. When macrophages are stimulated with an endotoxin, they produce a factor or factors, termed cachectin, that inhibits the activity of fat-producing (lipogenic) enzymes in cultured adipocytes. This effect may reflect one of the physiological bases for cachexia. In the present study, clones of complementary DNA from genes whose expression is increased during the differentiation of adipocytes were used to study the molecular basis of cachectin's actions. In the presence of cachectin, the expression of the corresponding genes was reversibly and specifically inhibited. Furthermore, when mature adipocytes were exposed to cachectin, the messenger RNA's of those genes diminished and rapidly approached the levels present before differentiation.

Spheroidal aggregate culture of rat liver cells: histotypic reorganization, biomatrix deposition, and maintenance of functional activities.

Abstract: Liver cells isolated from newborn rats and seeded on a non-adherent plastic substratum were found to spontaneously re-aggregate and to form, within a few days, spheroidal aggregates that eventually reached a plateaued diameter of 150-175 micron. Analyses on frozen sections from these spheroids by immunofluorescence microscopy using antibodies to various cytoskeletal elements and extracellular matrix components revealed a sorting out and a histotypic reorganization of three major cell types. A first type consisted of cells that segregated out on the aggregate surface forming a monolayer cell lining; a second type was identified as hepatocytes that regrouped in small islands often defining a central lumen; and a third group of cells reorganized into bile duct-like structures. This intercellular organization in the aggregates was paralleled by the accumulation of extracellular matrix components (laminin, fibronectin, and collagen) and their deposition following a specific pattern around each cell population structure. Determinations of albumin secretion and tyrosine aminotransferase induction by dexamethasone and glucagon at various times after the initiation of the cultures revealed a maintenance of the hepatocyte-differentiated functions for at least up to 2 mo at the levels measured at 3-5 d. It is concluded that cells dispersed as single cells from newborn rat liver conserve in part the necessary information to reconstruct a proper three-dimensional cyto-architecture and that the microenvironment so generated most likely represents a basic requirement for the optimal functioning of these differentiated cells.

Developmental regulation of T-cell receptor gene expression.

Abstract: In contrast to B cells or their antibody products, T lymphocytes have a dual specificity, for both the eliciting foreign antigen and for polymorphic determinants on cell surface glycoproteins encoded in the major histocompatibility complex (MHC restriction)1–4. The recent identification of T-cell receptor glycoproteins5–7 as well as the genes encoding T-cell receptor subunits will help to elucidate whether MHC proteins and foreign antigens are recognized by two T-cell receptors or by a single receptor. An important feature of MHC restriction is that it appears to be largely acquired by a differentiating T-cell population under the influence of MHC antigens expressed in the thymus8–10, suggesting that precursor T cells are selected on the basis of their reactivity with MHC determinants expressed in the host thymus9–11. To understand this process of ‘thymus education’, knowledge of the developmental regulation of T-cell receptor gene expression is necessary. Here we report that whereas messenger RNAs encoding the β-and γ-subunits are relatively abundant in immature thymocytes, α mRNA levels are very low. Interestingly, whereas α mRNA levels increase during further development and β mRNA levels stay roughly constant, γ mRNA falls to very low levels in mature T cells, suggesting a role for the γ gene in T-cell differentiation.

Differentiation-enhanced binding of the amino-terminal fragment of human urokinase plasminogen activator to a specific receptor on U937 monocytes.

Abstract: The purified amino-terminal fragment (ATF) of human urokinase plasminogen activator (residues 1-135), which is not required for activation of plasminogen, binds with high affinity to specific plasma membrane receptors on U937 monocytes. Intact urokinase efficiently competes for 125I-labeled ATF binding; 50% competition occurs with 1 nM urokinase. A large part of receptor-bound urokinase remains on the cell surface for at least 2 hr at 37 degrees C. Differentiation of U937 monocytes into macrophage-like cells specifically increases ATF binding 10- to 20-fold. These results suggest an important role for urokinase in monocyte/macrophage biology: the native enzyme binds to the cells with the amino-terminal domain; the catalytic, carboxyl-terminal domain remains exposed on the cell surface to stimulate localized proteolysis and facilitate cell migration.

The biology of cell reproduction

Abstract: PART I: BIOLOGY 1. The Cell Cycle Phases of the cell cycle Variability of the cell cycle 2. Nondividing Cells G0 cells Terminally differentiated cells 3. Populations of Cells Stem cells Transformed cells 4. Tissue Growth Growth in size Growth in number Doubling time Growth of tumors 5. Synchronization of Cells in the Cell Cycle Methods for synchronizing cells in culture Morphology of cells during the cell cycle PART II: CELL BIOLOGY 6. Temperature-Sensitive Mutants of the Cell Cycle Defining cell cycle mutants Conditional cell cycle mutants The execution point 7. Informational Content of Cells in Different Phases of the Cell Cycle Cell fusion Informational content of S phase cells Informational content of G0-G

Biological activities of laminin

Abstract: Laminin is a multifunctional protein with diverse biological activities. Like fibronectin, it can influence cell adhesion, growth, morphology, differentiation, migration, and agglutination as well as the assembly of the extracellular matrix. Laminin primarily affects cells of epithelial origin, and the response varies depending on the cell. Because most differentiated cells are difficult to maintain in culture, laminin may be an important supplement in studies on cell differentiation in vitro.

Mode of Action of Pituitary Growth Hormone on Target Cells

Abstract: Normal postnatal somatic growth becomes progressively dependent on GH with time. In contrast to other hormones, GH is the only hormone known to produce a dose-dependent stimulation of postnatal growth. Most of the effects attributed to GH action appear to be the result of a direct effect of GH on cells in different peripheral tissues, including cartilage. In addition to the growth-stimulating effect, GH has the intrinsic properties of being able to exert both insulin-like and insulin-antagonistic effects in adipose tissue and skeletal muscle. These two apparently antagonistic effects seem to be explained by the stage of responsiveness of the target cells to GH, which is determined by the previous influence of endogenous GH. An inhibition of adenylate cyclase with a concomitant decrease in intracellular cAMP might be an important early cellular event in the course of GH action, but it is not known whether or how this change in nucleotide metabolism relates to the various expressed effects of the hormone. The recognition that GH directly interacts with chondrocytes in cartilage suggests that alterations in the concentration of circulating somatomedins cannot be the only factor regulating skeletal growth. The recent discovery by Green and coworkers (42) demonstrating that GH specifically stimulates the differentiation of cloned preadipose cells and myoblasts in tissue culture may be a major breakthrough in the understanding of the mechanism of action of the growth-promoting effect of GH. Green (42) has proposed that GH directly stimulates terminal differentiation of cells in many different tissues including epiphyseal plate cartilage. The finding that GH binds specifically to cells in the resting cell zone but not to differentiated chondrocytes in the growth plate suggests that prechondrocytes in the growth plate are the target cells for GH action. If it is correct that GH directly stimulates the differentiation of prechondrocytes, we suggest that, during the process of chondrocyte differentiation in the growth plate, the genes that code for growth factors of the somatomedin class, such as IGF-I, are expressed. As a consequence, the clonal expansion of the chondrocytes in the proliferative zone of the growth plate that occurs in vivo during the process of normal growth is the result of this local production of growth factors.

Sarcoma viruses carrying ras oncogenes induce differentiation-associated properties in a neuronal cell line

Abstract: The growth-promoting and/or differentiation-blocking activities of Kirsten (Ki-MSV) or Harvey murine sarcoma virus (Ha-MSV) on various types of cells in vitro are well documented. Here we report an unexpected effect of these viruses on a rat phaeochromocytoma cell line, PC12. PC12 cells, which multiply indefinitely in growth medium, are known to respond to nerve growth factor (NGF) by cessation of cell division and expression of several properties resembling those of differentiated sympathetic neurones. We have found that Ki- and Ha-MSV mimic some, if not all, of the activities of NGF in PC12 cells, and there is evidence that the viral oncogenes, v-Ki-ras and v-Ha-ras, are responsible for this phenomenon. This system may be of value for studying the mechanism of action of the v-ras genes as well as the regulatory mechanism of growth and differentiation in neuronal cells.

Induction of transformation and continuous cell lines from normal human mammary epithelial cells after exposure to benzo[a]pyrene.

Abstract: Rapidly growing primary cultures of normal human mammary epithelial cells (HMEC) were exposed to 1 microgram of benzo[a]pyrene (B[a]P) per ml for two or three 24-hr periods. The B[a]P-treated populations consistently contained cells displaying a longer period of active growth in culture compared to the untreated control cells. Widespread heterogeneity in morphology and growth patterns was evidenced in these "extended life" (EL) cultures, with multiple sequential changes in these parameters occurring during the course of their life in culture. Two apparently immortal continuous cell lines have thus far emerged from these EL cultures. These lines have been characterized to be of human mammary epithelial origin and derived from the originally treated HMEC specimen. The continuous lines do not appear to be malignantly transformed as they do not cause tumor formation in nude mice and show little or no anchorage-independent growth. Nonetheless, they have acquired several properties characteristic of tumor-derived HMEC, which distinguish them from their normal progenitors. These cell lines, as well as the EL strains, may provide useful substrates for studies to determine what agents can induce further transforming events. Additionally, analysis of the multiple steps occurring in the El cultures, as well as in the emergence of the continuous cell lines, could potentially elucidate the processes occurring during human epithelial cell carcinogenesis and escape from senescence.

Environmental influences in the development of neural crest derivatives: glucocorticoids, growth factors, and chromaffin cell plasticity

Abstract: The neural crest gives rise to three major adrenergic cell types: sympathetic principal neurons, adrenal chromaffin cells, and small intensely fluorescent (SIF) cells. All of these derivatives synthesize and store catecholamines, but they differ in numerous other characteristics. SIF cells appear intermediate in phenotype between the other two. We have examined the role of several environmental factors in the differentiation of sympathetic principal neurons and adrenal chromaffin cells. In previous studies of young rat adrenal chromaffin cells in dissociated cell culture, differentiated characteristics such as the presence of the enzyme phenylethanolamine N-methyltransferase (PNMT), epinephrine (E) synthesis, and large catecholamine storage vesicles were not well maintained. Here we describe long-term culture of chromaffin cells which, in the presence of micromolar glucocorticoid, maintained all of these characteristics. In addition, chromaffin cells of a variety of ages were found to be dependent on glucocorticoid for long-term survival in culture. In the absence of glucocorticoid, many adrenal chromaffin cells from neonatal rats could be rescued by nerve growth factor (NGF) administration. They extended neurites, as previously described by Unsicker and colleagues (Unsicker, K., B. Krisch, U. Otten, and H. Thoenen (1978) Proc. Natl. Acad. Sci. U.S.A. 75: 3498–3502). In contrast to previous studies, however, with long-term exposure to NGF these cells became indistinguishable from mature sympathetic neurons, as judged by the following morphological and biochemical criteria: increased cell size and loss of intense CA fluorescence in their cell bodies; acquisition of characteristic neuronal ultrastructure, including morphologically specialized synapses; loss of chromaffin granules, PNMT, and E synthesis; and acquisition of neuron markers, including tetanus toxin labeling and immunoreactivity to neurofilament protein. This conversion to neurons was markedly enhanced by addition of a non-neuronal cell conditioned medium (CM) containing a neurite-promoting factor, which acted by increasing the NGF responsiveness of the chromaffin cells. Even chromaffin cells from adult rats, which are known to grow few processes in response to NGF alone, became neuronal in the presence of this CM plus NGF. While converting to neurons, adrenal chromaffin cells transiently assumed an intermediate phenotype resembling type I SIF cells, which suggests particular developmental relationships between the different cell types of the sympathoadrenal lineage.

SEROLOGICAL, BIOCHEMICAL, AND FUNCTIONAL IDENTITY OF B CELL-STIMULATORY FACTOR 1 AND B CELL DIFFERENTIATION FACTOR FOR IgG1

Abstract: By three criteria, we have demonstrated that B cell stimulatory factor (BSF-1) and B cell differentiation factor (BCDF-gamma) are the same lymphokine. Highly purified preparations of high performance liquid chromatography-purified or affinity-purified BSF-1 had BCDF-gamma activity but not BCDF-mu activity. A monoclonal anti-BSF-1 antibody coupled to Sepharose depleted both BSF-1 and BCDF-gamma activity but not BCDF-mu activity from two different T cell supernatants. Soluble monoclonal anti-BSF-1 blocked the BSF-1 and BCDF-gamma but not the BCDF-mu responses. These results suggest that BSF-1 acts on both resting and activated B cells to induce different effects.

Type beta transforming growth factor controls the adipogenic differentiation of 3T3 fibroblasts

Abstract: Differentiating mouse 3T3-L1 preadipocytes have been used as a model system to study the ability of type beta transforming growth factor (TGF-beta) to modulate cell development. We find that TGF-beta inhibits potently (ID50 approximately equal to 25 pM) the adipogenic conversion of 3T3-L1 cells. Inhibition is observed only when cells are exposed to TGF-beta before they become committed to differentiation. Even a transient (4 hr) exposure to TGF-beta immediately before the commitment point is sufficient to prevent differentiation. This point coincides with the time point immediately preceding the onset of coordinate expression of differentiation-specific proteins in 3T3-L1 cells. TGF-beta interacts with cell surface receptors in 3T3-L1 cells that have structural and binding properties similar to TGF-beta receptors in other cell types in which TGF-beta acts as a growth activator or a growth inhibitor. However, TGF-beta does not markedly alter differentiation-related mitosis in 3T3-L1 cells. The action of TGF-beta on 3T3-L1 cells does not involve changes in cAMP or prostaglandin E levels. These results suggest that TGF-beta is a unique modulator of adipogenic differentiation of fibroblasts.

Close link between reduction of c-myc expression by interferon and, G0/G1 arrest.

Abstract: It has recently been reported that c-myc is an inducible gene, regulated directly by growth signals which promote proliferation and expressed in a cell-cycle dependent manner Because various leukaemic cell lines express high levels of c-myc messenger RNA, it was of interest to discover whether the gene could be down-regulated in these cells by a growth inhibitor such as interferon (IFN) We show here that in Daudi Burkitt's lymphoma cells, IFN-alpha produces a five- to sevenfold reduction in c-myc mRNA through a decreased rate of c-myc gene transcription By isolating a growth-resistant Daudi cell variant that had escaped from this down-regulation, we provide the first clear link between reduction of c-myc mRNA and the IFN-mediated G0/G1 arrest characteristic of Daudi cells Furthermore, by screening other cell lines, we demonstrate the heterogeneity of human leukaemic cells with respect to these criteria Thus, IFN-alpha fails to reduce the c-myc mRNA and to change the cell-cycle distribution in HL-60 and U937 cells, although normal induction of other IFN-regulated activities takes place The latter group of cells shows a decline in c-myc gene expression when they become arrested in the G0/G1 phase as part of their terminal differentiation