Search PubMed⌕ Search

Biomedical subjects

N B Gilula

Publications and source records attributed to N B Gilula.

At least 73 records · Page 4Linked to original sources
PubMed1987

Selective disruption of gap junctional communication interferes with a patterning process in hydra.

The cells that make up the body column of hydra are extensively joined by gap junctions, capable of mediating the rapid exchange of small hydrophilic molecules between the cytoplasms of neighboring cells. Both the rate of transfer of small molecules through the gap junctions and the rate of return of gap junction coupling after grafting experiments are sufficiently rapid to mediate events in the patterning of hydra tissue. Antibodies to the major rat liver gap junction protein (27,000 daltons) recognize a gap junction antigen in hydra and are effective in eliminating junctional communication between hydra cells. The antibodies perturb the head inhibition gradient in grafting operations, suggesting that cell-cell communication via gap junctions is important in this defined tissue patterning process.

Animals↗
PubMed1987

Topological analysis of the major protein in isolated intact rat liver gap junctions and gap junction-derived single membrane structures.

The topological organization of the major rat liver gap junction protein has been examined in intact gap junctions and gap junction-derived single membrane structures. Two methods, low pH and urea at alkaline pH, were used to "transform" or "split" double membrane gap junctions into single membrane structures. Low pH treatment "transforms" rat liver gap junctions into small single membrane vesicles which have an altered sodium dodecyl sulfate-polyacrylamide gel electrophoresis profile after digestion with L-1-to-sylamido-2-phenylethylchloromethyl ketone-trypsin. Alkaline pH treatment in the presence of 8 M urea can split isolated rat liver gap junctions into single membrane sheets which have no detectable structural alteration or altered sodium dodecyl sulfate-polyacrylamide gel electrophoresis profile after proteolytic digestion, suggesting that these single membrane sheets may be useful for topological studies of the gap junction protein. Proteolytic digestion studies have been used to localize the carboxyl terminus of the molecule on the cytoplasmic surface of the intact gap junction. However, the amino terminus does not appear to be accessible to proteases or to interaction with an antibody that is specific for the amino-terminal region of the molecule in intact or split gap junctions. Binding of antibodies, that block junctional channel conductance, can be eliminated by proteolytic digestion of intact gap junctions, suggesting that all antigenic sites for these antibodies are located on the cytoplasmic surface of the intact gap junction. In addition, calmodulin gel overlays indicate that at least two calmodulin binding sites exist on the cytoplasmic surface of the junctional protein. The information generated from these studies has been used to develop a low resolution two-dimensional model for the organization of the major rat liver gap junctional protein in the junctional membrane.

Amino Acid Sequence↗
PubMed1987

Functional assembly of gap junction conductance in lipid bilayers: demonstration that the major 27 kd protein forms the junctional channel.

Gap junctions isolated from rat liver were incorporated into planar lipid bilayers. A channel activity that was directly dependent on voltage was recorded. Changes of pH and (Ca2+) had no direct effect on channel activity; however, they modulated the voltage-dependent gating of the gap junction channels differently. Single-channel fluctuations showed large scatter with peak amplitudes of 140 and 280 picoSiemmens in 0.1 M NaCl. The major protein of gap junctions (Mr of 27 kd) was also reconstituted into bilayers, giving channel properties similar to those of intact gap junctions. Polyclonal antibodies specific for this protein caused inhibition of the junctional conductance in bilayers. These data provide direct evidence that the 27 kd protein is the molecular species responsible for gap junction communication between cells.

Animals↗
PubMed1987

Topology of gap junction protein and channel function.

This paper presents recent results from this laboratory concerning the topological structure and function of the major 27 kDa gap junction protein. Immunological, biochemical and biophysical observations now provide evidence for the localization of the 27 kDa protein to gap junction structures, both in vivo and in vitro, and for the participation of the 27 kDa protein in channel conductance.

Animals↗
PubMed1986

Cloning and characterization of human and rat liver cDNAs coding for a gap junction protein.

An extended synthetic oligonucleotide (58-mer) has been used to identify and characterize a human liver gap junction cDNA. The cDNA is 1,574 bases long and contains the entire coding region for a gap junction protein. In vitro translation of the RNA products of this cDNA is consistent with it coding for a 32,022-D protein. Southern blot analysis indicates that the gap junction gene is present as a single copy, and that it can be detected in a variety of organisms using the human liver cDNA as a probe. The human cDNA has been used to screen a rat liver cDNA library, and a rat liver junction cDNA clone has been isolated. The rat liver clone is 1,127 bases in length, and it has strong sequence homology to the human cDNA in the protein-coding region, but less extensive homology in the 3'-untranslated region.

Amino Acid Sequence↗
PubMed1985

Interaction of calmodulin and other calcium-modulated proteins with mammalian and arthropod junctional membrane proteins.

Calmodulin and other calcium-modulated proteins bind in vitro to purified junctional polypeptides from rat liver gap junctions, bovine lens fiber junctions, a chymotryptic fragment from bovine lens junctions, and crayfish hepatopancreas gap junctions. The potential biological relevance of the interaction of calmodulin with junctional proteins is suggested by immunocytochemical localization of endogenous calmodulin in cortical regions of the cell where gap junctions exist. These observations provide a molecular basis for understanding the potential regulatory role of calmodulin on cell-cell communication channels in vivo. In addition, the calmodulin binding represents the first molecular homology that has been found for junctional channel proteins from mammalian and arthropod tissues.

Animals↗
PubMed1984

The biosynthesis of gap junctions.

This brief presentation is designed to review the descriptive information available on the formation of gap junctions between cells, and to discuss the recent progress that has been made on studying the biosynthesis of junctional polypeptides in both cell-free systems and intact tissue.

Animals↗
PubMed1982

Comparative analysis of the major polypeptides from liver gap junctions and lens fiber junctions.

Gap junctions from rat liver and fiber junctions from bovine lens have similar septilaminar profiles when examined by thin-section electron microscopy and differ only slightly with respect to the packing of intramembrane particles in freeze-fracture images. These similarities have often led to lens fiber junctions being referred to as gap junctions. Junctions from both sources were isolated as enriched subcellular fractions and their major polypeptide components compared biochemically and immunochemically. The major liver gap junction polypeptide has an apparent molecular weight of 27,000, while a 25,000-dalton polypeptide is the major component of lens fiber junctions. The two polypeptides are not homologous when compared by partial peptide mapping in SDS. In addition, there is not detectable antigenic similarity between the two polypeptides by immunochemical criteria using antibodies to the 25,000-dalton lens fiber junction polypeptide. Thus, in spite of the ultrastructural similarities, the gap junction and the lens fiber junction are comprised of distinctly different polypeptides, suggesting that the lens fiber junction contains a unique gene product and potentially different physiological properties.

Animals↗
PubMed1980

Synaptogenesis in the vestibular sensory epithelium of the chick embryo.

The formation of synapses between sensory cells and the terminals of afferent axons has been examined in the embryonic chick labyrinth. Neurites initially cross the otocyst basal lamina and ramify among the undifferentiated epithelial cells by stage 25 Hamburger and Hamilton. At the same time granular vesicles, with diameters averaging 130nm, appear in the basal cytoplasm of a few of the epithelial cells. These vesicles often exist in groups at sites contact with; neurites. By stages 27-28, non membrane-bound densities are frequently found in association with groups of granular vesicles at the plasma membrane. Smaller, clear synaptic vesicles are also a prominent component of these arrangements in presumptive hair cells. Presynaptic ribbons opposite postsynaptic densites are identifiable at about stage 28, and their number increases during subsequent embryonic stages. Specialized appositions, including adherent, postsynaptic and possibly gap junctional contacts, join epithelial cells and nerve terminals throughout this period. The distribution of these junctions is variable, and is not necessarily correlated with the sites of formation of presynaptic ribbons. By stage 32, well-developed chemical synapses consisting of presynaptic ribbons witah vesicle halos and postsynaptic densities are common features of hair cell-afferent nerve terminal contact regions. In addition, possible sites of gap junctional contact between adjacent intra-epithelial nerve endings found at stage 32 presage those found in the cristae and maculae of pre-hatch (stage 45) embryos and adults.

Animals↗