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Biomedical subjects

G M Edelman

Publications and source records attributed to G M Edelman.

At least 235 records · Page 13Linked to original sources
PubMed1982

A neural cell adhesion molecule from human brain.

We have used a crossreactive monoclonal antibody against a mouse neural cell adhesion molecule (N-CAM) to characterize and purify an antigen from embryonic and neonatal human brain. This antigen was identified as human N-CAM according to several criteria, including molecular weight, sialic acid content, amino acid composition, analysis of peptide fragments, reactivity with a variety of anti-CAM antibodies, and activity of the antigen in assays of cell and membrane vesicle aggregation. The findings make feasible an exploration of the possible role of N-CAM in various neurological disorders.

Amino Acids↗
PubMed1982

Cell adhesion molecules in early chicken embryogenesis.

N-CAM, the neural cell adhesion molecule, has been found at a number of regions in the early (1-5 days) chicken embryo by fluorescent antibody techniques. These regions appear to be those concerned with induction of the primary developmental axis (neural plate, neural tube, notochord, somites) or those in which later inductive events occur (neural crest cells, optic, otic, and pharyngeal placodes, cardiac mesoderm, mesonephric primordium, limb buds). The staining patterns in the latter group of regions are highly dynamic and transient and are limited to the epithelial components of the placodes and to the precursors of mesonephric tubules. In neural crest cells, N-CAM appears early, disappears during migration of the cells on fibronectin, and reappears at sites where ganglia are formed. In other regions of the nervous system, particularly those related directly to the neural tube, the N-CAM molecule is stained at all stages. The results raise the possibility that adhesion mediated by N-CAM plays a primary role in early embryogenesis as well as in later histogenesis.

Brain↗
PubMed1982

Embryonic to adult conversion of neural cell adhesion molecules in normal and staggerer mice.

The neural cell adhesion molecule (N-CAM) has an unusually high amount of sialic acid (28-35 g/100 g of polypeptide) and shows microheterogeneity in electrophoretic gels in its embryonic or E form. During development, the molecule undergoes conversion to several adult or A forms, which resemble the E form but which on the average have only 10% sialic acid and do not appear to be microheterogeneous. In the present study, rabbit antibodies to mouse N-CAM and two different monoclonal antibodies were used to follow the E leads to A conversion in normal and mutant mice. E leads to A conversion to three forms (Mr 180,000, Mr 140,000, and Mr 120,000) was found to occur at different rates in different parts of the brains of wild-type mice. Examination of the entire cerebellum of the granuloprival mouse mutant staggerer (sg/sg) showed that the E leads to A conversion did not occur by 21 days after birth, whereas in wild type it was almost complete at that time. There was also some delay in E leads to A conversion within the cerebral cortex of sg/sg, although phenotypically no evidence of cortical disorder has been detected. In pooled tissues from phenotypically normal-appearing littermates, (i.e., a mixture of sg/+ and +/+), a slight conversion delay was also found in cerebellum and cortex. The mutants weaver, reeler, and jimpy all showed normal schedules of E leads to A conversion. These observations raise the possibility that a major defect in staggerer mutants relates to a failure in local surface modulation of N-CAM to produce the A forms of the molecule. Some of the failures of synapse formation and of cell survival seen in this disease may result from the anomaly, which is likely to alter the binding properties of N-CAM at critical times of development.

Aging↗
PubMed1982

Selective networks capable of representative transformations, limited generalizations, and associative memory.

Two parallel sets of selective networks composed of intercommunicating neuron-like elements have been connected to produce a new kind of automaton capable of limited recognition of two-dimensional patterns. Salient features of this automaton are (i) preestablished unchanging connectivity, (ii) preassigned connection strengths that are selectively altered according to experience, (iii) local feature detection in one network with simultaneous global feature correlation in the other, and (iv) reentrant interactions between the two networks to generate a new function, associative memory. No forced learning, explicit semantic rules, or a priori instructions are used.

Computers↗
PubMed1981

Lateral diffusion of surface molecules in animal cells and tissues.

When bound to cell surfaces, certain lectins such as concanavalin A induce a drop in the average diffusion coefficients (D) of a number of cell surface molecules. To find whether such anchorage modulation occurs naturally, D of surface antigens on different cell and tissue types were measured by fluorescence photobleaching recovery. Values for cells of the same tissue origin under different conditions of growth and association - in tissues, in small aggregates, and as isolated cells - varied by less than twofold when polyspecific monovalent antibodies to cell surface antigens were used, a range much less than the sixfold decrease in D observed after lectin-induced anchorage modulation. Thus, if reversible modulation of the diffusion rate is used naturally as a means of cell signaling, it must involve only a few kinds of surface receptors not detected by the antibodies used in this study. In certain tissues, however, a significant proportion of cells showed no apparent receptor mobility. This "all or none" modulation of lateral diffusion may reflect relatively long-lasting alterations in the states of a single cell type or differentiation among the cells of the particular tissue.

Animals↗
PubMed1981

Distinct calcium-independent and calcium-dependent adhesion systems of chicken embryo cells.

Three criteria have been used to distinguish among different systems of embryonic cell adhesion: dependence on Ca2+, involvement of particular cell-surface molecules, and binding specificity. The characterization of the adhesion with respect to cell-surface molecules was carried out by using specific antibodies against the neural and liver cell adhesion molecules (N-CAM and L-CAM) and antibodies raised against retinal cells prepared by limited trypsinization in the presence of Ca2+ (called "T/Ca cells"). Aggregation of cells prepared from retina or brain without Ca2+ did not require Ca2+ and was inhibited by anti-(N-CAM) antibodies but not by anti-(L-CAM) or anti-T/Ca cell antibodies. In contrast, cells obtained from the same tissues in the presence of Ca2+ did require Ca2+ to aggregate. This aggregation was inhibited by anti-T/Ca cell antibodies but not by anti-(N-CAM) or anti-(L-CAM) antibodies. Hepatocyte aggregation also required Ca2+ and was inhibited only by anti-(L-CAM) antibodies. These results define three antigenically distinct cell adhesion systems in the embryo and raise the possibility that additional systems will be found. The neural Ca2+-independent system displayed a limited tissue specificity, mediating binding to neural but not liver cells. In contrast, the Ca2+-dependent systems of both neural and liver cells caused binding to all cell types tested. The Ca2+-dependent system was most active in retinal cells from 6-7 day embryos, whereas the Ca2+-independent system was most active at later times during development. In addition, treatments that inhibited the Ca2+-independent or Ca2+-dependent systems had very different effects on the fasciculation of neurites from dorsal root ganglia. All of the results suggest that Ca2+-independent and Ca2+-dependent adhesion systems play different functional roles during embryogenesis.

Animals↗
PubMed1980

Antibodies to a neural cell adhesion molecule disrupt histogenesis in cultured chick retinae.

Cell-surface proteins are believed to have important roles in cell-cell interactions during brain development, particularly in such processes as cellular adhesion, neurite outgrowth and synapse formation. The chick neural cell adhesion molecule, CAM, is a cell-surface protein specific to the nervous system and has been implicated in cell adhesion among cells and neurites of the developing retina and brain. Previous studies have shown that F(ab') fragments of antibodies directed against CAM inhibit the in vitro aggregation of cells obtained from 9-day embryonic chick retina. The specific antibody fragments also reduce the diameter of neurite fascicles that grow out from cultured dorsal root ganglia, apparently by blocking side-to-side adhesion between the neurites. In addition, anti-CAM antibodies alter the appearance of histotypic patterns in retinal cell aggregates maintained in culture for several days. We now demonstrate that the antibodies can disrupt histogenesis of the developing retina in organ culture, strengthening the notion that the cell-cell adhesion properties mediated by CAM are involved in the normal development of histological layers in the chick retina.

Animals↗
PubMed1980

Density-dependent stimulation and inhibition of cell growth by agents that disrupt microtubules.

We have previously reported that agents that disrupt microtubules, such as colchicine, inhibit the growth stimulation of lymphocytes and arrested fibroblasts; other workers have recently reported enhanced stimulation of fibroblasts in the presence of the same drugs. In the present studies, we resolve this conflict by demonstrating that the stimulatory and inhibitory effects of microtubule disruption depend upon the density and the cell type of the treated cultures. Our analysis included an examination of three variables: (i) cell density (sparse or confluent), (ii) cell type (resting fibroblasts from mouse or chicken embryos or from the permanent 3T3 mouse fibroblast line), and (iii) treatment with colchicine and related drugs in the presence or absence of various mitogens such as serum, insulin, and epidermal growth factor. We found that colchicine augmented mitogenesis in confluent cultures of all cell types. Colchicine by itself appeared to be mitogenic only for confluent chicken embryo fibroblasts. In sparse cultures with minimal cell-cell contacts, however, there were differences between embryonic cells and the 3T3 cell line. In confirmation of our previous reports, disruption of microtubules by colchicine inhibited the mitogenic stimulation of sparse cultures of embryonic chicken or mouse fibroblasts. In contrast, fibroblasts of the permanent 3T3 line in sparse cultures were stimulated by some mitogens despite the presence of colchicine. The augmentative effects of colchicine on the stimulation of confluent cultures were synergistic with the mitogens, and colchicine allowed response to otherwise submitogenic doses of growth factors. Kinetic studies indicated that the stimulatory and inhibitory effects of colchicine are separable and that both can operate simultaneously. The experiments suggest that the regulation of growth by nutrient deprivation and the regulation by density dependence proceed at least in part by different mechanisms. All of the results suggest that microtubular integrity can be associated with the expression of either negative or positive controls on cell growth, depending upon the confluence or lineage of the cells in culture.

Animals↗
PubMed1980

Association of the 2-micron DNA plasmid with yeast folded chromosomes.

The 2-micron DNA plasmid cosedimented in sucrose gradients with the folded chromosome on centrifugation of lysates from logarithmically growing yeast cells. It banded with both the slow-sedimenting g1 form derived from prereplicative cells and the fast-sedimenting g2 form from postreplicative cells. When cells were induced to withdraw from the cell cycle by nitrogen starvation, the folded chromosome was converted to the g0 form, which sedimented more slowly than the g1 form, and only 1/10th the amount of 2-micron DNA cosedimented with this g0 form as compared to the logarithmic-phase forms, g1 and g2. Expression of the temperature-sensitive cell division cycle (cdc) 28 mutation, which defines the "start" of the cell cycle, resulted in a rapid alteration in the folded chromosome sedimentation pattern, and less than 20% of the 2-micron DNA cosedimented with the folded chromosome. These results raise the possibility that association of the 2-micron DNA plasmid with structures in the cell corresponding to the folded chromosome is subject to cell division cycle control.

Cell Cycle↗
PubMed1980

Structure of the heavy chain of the H-2Kk histocompatibility antigen.

We have used radiochemical techniques to characterize the heavy chain (Mr 46,000) of the murine H-2Kk histocompatibility antigen in terms of six fragments (I-VI) obtained after cleavage of the polypeptide chain with CNBr. The tentative order of the fragments, which account for more than 90% of the heavy chain, was assigned by radiochemical sequence analysis of the intact heavy chain and of each purified CNBr fragment and by analysis of the CNBr fragments obtained from the large papain fragment of the heavy chain. Treatment of cells with tunicamycin yielded H-2 molecules with heavy chains of molecular weight 40,000, suggesting that the carbohydrate moieties have a combined molecular weight of approximately 6000. CNBr cleavage of H-2Kk heavy chains labeled with [3H]fucose indicated that the carbohydrate moieties are located on fragments II and IV.. Incubation of cells with 32PO4 gave H-2 molecules with radioactive phosphoserine in the carboxyl-terminal CNBr fragment (VI) of the heavy chain and in the fraction containing beta 2-microglobulin. Sequence analysis of each CNBr fragment intrinsically labeled with 3H- and 35S-labeled amino acids identified a total of 87 residues in the H-2Kk heavy chain. The sequence closely resembles that of the H-2Kb molecule, and the 11 differences are scattered throughout the polypeptide chain. Comparison with HLA sequences indicates that the two allelic H-2 sequences are more closely related to each other (88% identity) than either is to the HLA-B7 or A2 antigens (approximately 70%). Similarly, the nonallelic HLA antigens are more closely related to each other (83%) than either is to the H-2Kk or H-2Kb molecules.

Amino Acid Sequence↗
PubMed1980

A cell surface molecule involved in aggregation of embryonic liver cells.

Aggragation of chicken enbryo hepatocytes can be inhibited by Fab' fragments of antibodies prepared against the cells. An aqueous extract of liver cell membranes contained antigens that neutralized the adhesion-blocking properties of the Fab' fragments. This neutralization activity was associated with a polypeptide of Mr68,000 in NaDodSO4; the polypeptide was distinct from serum albumin. Specific antibodies prepared against the 80-fold purified active fraction inhibited liver cell adhesion and immunoprecipitated the 68,000 Mr polypeptide from active fractions as well as from a detergent extract of liver cell membranes. In hepatocyte cultures, Fab' fragments of antibodies against the liver molecule prevented both colony formation and appearance of histotypic patterns. Liver cell adhesion was compared at the cellular and molecular levels to that of embryonic neural retina cells. Antibodies against the cell adhesion molecule from neural tissue inhibited retinal but not liver cell aggregation; conversely, antibodies against the liver polypeptide inhibited liver but not retinal cell aggregation. By means of antibody absorption and immunoprecipitation, it was confirmed that the two cell adhesion molecules are antigenically unrelated.

Animals↗
PubMed1980

Effects of fasciculation on the outgrowth of neurites from spinal ganglia in culture.

This report describes the influence of neurite fasciculation on two aspects of nerve growth from chick spinal ganglia in vitro: the inhibition of outgrowth by high concentrations of nerve growth factor (NGF) and the preferential growth of neurites toward a capillary tube containing NGF. These studies involved a comparison of cultures of single cells, cell aggregates, and intact ganglia and the use of antibodies against the nerve cell adhesion molecule (CAM) to perturb fasciculation under a variety of conditions. The inhibition of outgrowth, which was observed with ganglia and aggregates but not with single cells, was correlated with a thickening of neurite fascicles. In accord with this observation, anti-CAM, which diminishes fasciculation by inhibiting side-to-side interactions between individual neurites, also partially reversed the inhibition of neurite outgrowth at high NGF concentrations. On the basis of these and other studies, we consider the possibility that neurite bundling causes an increase in the elastic tension of a fascicle without a compensatory increase in its adhesion to substratum. It is proposed that this imbalance could inhibit neurites from growing out from a ganglion and even result in retraction of preexisting outgrowth. In the analysis of NGF-directed growth, it was found that a capillary source of NGF produced a steep but transient NGF gradient that subsided before most neurites had emerged from the ganglion. Nevertheless, the presence of a single NGF capillary caused a dramatic and persistent asymmetry in the outgrowth of neurites from ganglia or cell aggregates. In contrast, processes of individual cells did not appear to orient themselves toward the capillary. The most revealing finding was that anti-CAM antibodies caused a decrease in the asymmetry of neurite outgrowth. These results suggest that side-to-side interactions among neurites can influence the guidance of nerve bundles by sustaining and amplifying an initial directional signal.

Animals↗
PubMed1979

Characterization of the protein kinase activity of avian sarcoma virus src gene product.

The avian sarcoma virus src gene product, p60src, has been purified 650-fold from cytoplasmic extracts of the rat tumor cell line RR1022 by using ammonium sulfate fractionation, hydrophobic chromatography on omega-aminohexyl agarose, and ion exchange chromatography on phosphocellulose. Partially purified p60src is a monomer, with a native molecular weight of about 60,000 and an apparent pI of 6.0. In immunoprecipitates, p60src catalyzed phosphorylation of anti-p60src IgG heavy chains within the variable (VH) domain, which contains the heavy chain portion of the antigen combining site. Crude preparations of p60src contained phosphatase activity able to cleave phosphate from IgG heavy chains; this activity was removed by the purification procedure, and partially purified p60src could phosphorylate the heavy chain of specific antibody in solution. Furthermore, purified p60src catalyzed phosphorylation in solution of the general protein kinase substrate, alpha-casein, strengthening the hypothesis that it may in fact function as a protein kinase in vivo.

Alpharetrovirus↗
PubMed1979

Replication in vitro of the 2-micrometer DNA plasmid of yeast.

Cell-free extracts prepared from growing cells of the budding yeast Saccharomyces stimulated DNA synthesis directed by the supercoiled 2-micrometer yeast DNA plasmid. The major products of the reaction were open-circular daughter molecules possessing newly synthesized full-length linear DNA strands. Some of these were ligated and supertwisted by the extracts to yield a supercoiled DNA product. Both of the complementary DNA strands of the template were replicated. In addition, the extracts induced the appearance of theta-forms of the plasmid DNA, which are presumed to be replicative intermediates. The results of experiments utilizing BrdUTP incorporation indicated that DNA repair did not contribute significantly to the overall reaction. Extracts prepared from the cell division cycle mutants cdc7 and cdc8, held in culture at the nonpermissive temperature, possessed diminished activity. Because these mutants define a dependent sequence of events leading from the start of the cell cycle through G1 to S phase, this result suggests that the activity that stimulates 2-micrometer DNA replication in vitro is subject to control in the yeast cell cycle.

DNA↗
PubMed1979

Favin versus concanavalin A: Circularly permuted amino acid sequences.

We have determined the tentative amino acid sequence of the beta chain (M(r) 20,000) of the lectin favin. In previous studies, we have shown that the alpha chain (M(r) 5600) of this lectin is homologous to a region in the middle of the concanavalin A (Con A) sequence (residues 70-119). Now we present evidence that the beta chain is homologous to two discrete segments of Con A. The homology begins at residue 120 of Con A, extends to the COOH terminus (residue 237) and continues without interruption through the NH(2)-terminal 69 residues of Con A. Together, the alpha and beta chains of favin account for a polypeptide chain equivalent in size to that of Con A. The comparison of the two proteins thus reveals a circular permutation of extensive homologous sequences. The favin molecule contains residues identical to many of the residues postulated to be involved in sugar binding by Con A, and contains all of the direct metal ligands as well as residues homologous to most of the residues that form the beta-pleated sheets of Con A. These homologies suggest that the three-dimensional structures of the two lectins are likely to be very similar. Moreover, favin appears to be even more closely related in primary structure and sugar specificity to the lectins from pea and lentil, raising the possibility that all of these lectins may have structures that resemble Con A. Some of these similarities may also extend to the lectins from soybean, peanut, and red kidney bean, which have different sugar specificities but share sequence homologies with the favin beta chain.

Journal Article↗