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D R Colman

Publications and source records attributed to D R Colman.

70 records · Page 4Linked to original sources
PubMed1989

Mechanisms of cell adhesion in the nervous system: role of the immunoglobulin gene superfamily.

The amino acid sequences of a large number of the cell surface proteins known to mediate cell-cell interactions in the nervous system have recently been reported. Many of these proteins are members of the immunoglobulin gene superfamily and have remarkably similar structures and amino acid sequences in their extracellular segments. We have termed this family of immunoglobulin-related cell adhesion molecules the Ig-CAMs. In this article, we review the structural features of the Ig-CAMs, discuss how these features may relate to the role of these proteins in mediating cell adhesion and cell signaling events, and finally consider the evolutionary origins of this family of proteins.

Animals↗
PubMed1988

Chromosomal locations of genes encoding 2',3' cyclic nucleotide 3'-phosphodiesterase and glial fibrillary acidic protein in the mouse.

Cyclic nucleotide phosphodiesterase (CNP) and glial fibrillary acidic protein (GFAP) are useful markers of myelin and astroglia, respectively. Two proteins with CNP activity are known to exist in brain and lymphoid tissues. They appear to be the products of several distinct but related messenger ribonucleic acid (mRNA) species. GFAP is a single protein encoded by a single mRNA. We have localized the GFAP gene to distal chromosome 11 in the mouse. There are two genetic loci identified by CNP probes, one is closely linked to the GFAP gene, and the other maps to chromosome 3.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗
PubMed1988

Cellular and subcellular distribution of 2',3'-cyclic nucleotide 3'-phosphodiesterase and its mRNA in the rat central nervous system.

The 2',3'-cyclic nucleotide 3'-phosphodiesterases (CNPs) are closely related oligodendrocyte proteins whose in vivo function is unknown. To identify subcellular sites of CNP function, the distribution of CNP and CNP mRNA was determined in tissue sections from rats of various developmental ages. Our results indicate that CNP gene products were expressed exclusively by oligodendrocytes in the CNS. CNP mRNA was concentrated around oligodendrocyte perinuclear regions during all stages of myelination. Developmentally, initial detection of CNP mRNA closely paralleled initial detection of its translation products. In electron micrographs of immunostained ultrathin cryosections, CNP was associated with oligodendrocyte membranes during the earliest phase of axonal ensheathment. In more mature fibers, immunocytochemistry established that the CNPs are not major components of compact myelin but are concentrated within specific regions of the oligodendrocyte and myelin internode. These include (a) the plasma membrane of oligodendrocytes and their processes, (b) the periaxonal membrane and inner mesaxon, (c) the outer tongue process, (d) the paranodal myelin loops, and (e) the "incisure-like" membranes found in many larger CNS myelin sheaths. A cytoplasmic pool of CNP was also detected in oligodendrocyte perikarya and larger oligodendrocyte processes. CNP was also enriched in similar locations in myelinated fibers of the PNS.

2',3'-Cyclic Nucleotide 3'-Phosphodiesterase↗
PubMed1988

Chromosomal location of the mouse gene that encodes the myelin-associated glycoproteins.

The two myelin-associated glycoprotein (MAG) species, designated large MAG (L-MAG) and small MAG (S-MAG), are believed to be generated by differential splicing from a single RNA transcript. We have now defined the genetic locus encoding the two MAG proteins in the mouse. Analysis of a panel of interspecies somatic cell hybrids indicated that all MAG coding sequences reside on chromosome 7. Following the inheritance of a restriction fragment length polymorphism associated with MAG coding sequences allowed the locus to be positioned 0.5 centimorgans from the locus Abpa (androgen binding protein alpha) on proximal chromosome 7. These data strongly support the hypothesis that a single gene encodes the two MAG proteins, and we propose the name Mag for this locus. This localization places Mag in close proximity to the neurological mutant locus qv (quivering) and raises the possibility of a functional relationship or identity between Mag and qv. However, an analysis of the MAG gene, its RNA transcripts, and its protein products revealed no abnormalities in homozygous qv mutant mice, suggesting that this chromosomal linkage is not etiologically significant.

Animals↗
PubMed1987

Isolation and characterization of cDNA clones for rat ribophorin I: complete coding sequence and in vitro synthesis and insertion of the encoded product into endoplasmic reticulum membranes.

Ribophorins I and II are two transmembrane glycoproteins that are characteristic of the rough endoplasmic reticulum and are thought to be part of the apparatus that affects the co-translational translocation of polypeptides synthesized on membrane-bound polysomes. A ribophorin I cDNA clone containing a 0.6-kb insert was isolated from a rat liver lambda gtll cDNA library by immunoscreening with specific antibodies. This cDNA was used to isolate a clone (2.3 kb) from a rat brain lambda gtll cDNA library that contains the entire ribophorin I coding sequence. SP6 RNA transcripts of the insert in this clone directed the in vitro synthesis of a polypeptide of the expected size that was immunoprecipitated with anti-ribophorin I antibodies. When synthesized in the presence of microsomes, this polypeptide, like the translation product of the natural ribophorin I mRNA, underwent membrane insertion, signal cleavage, and co-translational glycosylation. The complete amino acid sequence of the polypeptide encoded in the cDNA insert was derived from the nucleotide sequence and found to contain a segment that corresponds to a partial amino terminal sequence of ribophorin I that was obtained by Edman degradation. This confirmed the identity of the cDNA clone and established that ribophorin I contains 583 amino acids and is synthesized with a cleavable amino terminal insertion signal of 22 residues. Analysis of the amino acid sequence of ribophorin I suggested that the polypeptide has a simple transmembrane disposition with a rather hydrophilic carboxy terminal segment of 150 amino acids exposed on the cytoplasmic face of the membrane, and a luminal domain of 414 amino acids containing three potential N-glycosylation sites. Hybridization measurements using the cloned cDNA as a probe showed that ribophorin I mRNA levels increase fourfold 15 h after partial hepatectomy, in confirmation of measurements made by in vitro translation of liver mRNA. Southern blot analysis of rat genomic DNA suggests that there is a single copy of the ribophorin I gene in the haploid rat genome.

Amino Acid Sequence↗
PubMed1987

The amino acid sequences of the myelin-associated glycoproteins: homology to the immunoglobulin gene superfamily.

The myelin associated glycoproteins (MAG) are integral plasma membrane proteins which are found in oligodendrocytes and Schwann cells and are believed to mediate the axonal-glial interactions of myelination. In this paper we demonstrate the existence in central nervous system myelin of two MAG polypeptides with Mrs of 67,000 and 72,000 that we have designated small MAG (S-MAG) and large MAG (L-MAG), respectively. The complete amino acid sequence of L-MAG and a partial amino acid sequence of S-MAG have been deduced from the nucleotide sequences of corresponding cDNA clones isolated from a lambda gt11 rat brain expression library. Based on their amino acid sequences, we predict that both proteins have an identical membrane spanning segment and a large extracellular domain. The putative extracellular region contains an Arg-Gly-Asp sequence that may be involved in the interaction of these proteins with the axon. The extracellular portion of L-MAG also contains five segments of internal homology that resemble immunoglobulin domains, and are strikingly homologous to similar domains of the neural cell adhesion molecule and other members of the immunoglobulin gene superfamily. In addition, the two MAG proteins differ in the extent of their cytoplasmically disposed segments and appear to be the products of alternatively spliced mRNAs. Of considerable interest is the finding that the cytoplasmic domain of L-MAG, but not of S-MAG, contains an amino acid sequence that resembles the autophosphorylation site of the epidermal growth factor receptor.

Amino Acid Sequence↗
PubMed1987

Complete amino acid sequence and in vitro expression of rat NF-M, the middle molecular weight neurofilament protein.

A lambda gtII expression library was prepared from rat brain and screened with a polyclonal antiserum, which recognizes both NF-H and NF-M. An NF-M cDNA clone (pNF-M3C = 1.6 kb) was isolated and characterized. The fusion protein of NF-M3C, when used as an affinity matrix for the anti-neurofilament serum, isolated a subpopulation of antibodies specific for NF-M. Northern analysis demonstrates a single band of approximately 3000 nt and a constant message level for NF-M during postnatal development from postnatal day 0 (PO) to adulthood. Using pNF-M3C as a probe, a second cDNA clone was isolated from a lambda gtII rat brain expression library (pNF-M2D = 2.7 kb). The 2 clones were sequenced and pNF-M2D was found to encode the entire rat NF-M protein. The calculated molecular weight is 95,600, which is only 65% of the molecular weight determined by SDS-PAGE. The amino acid sequence of rat NF-M shows the conserved rod segment present in all intermediate filament proteins. The molecule also contains an unusual C-terminal extension with stretches of glutamic acid, which could contribute to the anomalous migration of this protein on SDS-PAGE and the fact that NF-M does not readily assemble into filaments. The pNF-M2D clone was transcribed and translated in vitro utilizing a rabbit reticulocyte lysate system. The resulting radiolabeled translation products were unexpectedly shown to comigrate with purified rat NF-M on 1- and 2-dimensional gels, even though the translated protein is not phosphorylated.

Amino Acid Sequence↗
PubMed1987

Molecular cloning of a 2',3'-cyclic nucleotide 3'-phosphodiesterase: mRNAs with different 5' ends encode the same set of proteins in nervous and lymphoid tissues.

Antibodies raised to a mixture of the 46 and 48 kDa rat CNS 2',3'-cyclic nucleotide 3-phosphodiesterases (CNPs) recognized apparently identical proteins in peripheral nervous system (PNS), thymus, and circulating blood lymphocytes. These antibodies were used to identify, in a rat brain phage lambda gt11 expression library, cDNA clones encoding beta-galactosidase-CNP fusion proteins, some of which showed CNP activity. In RNA blots, the subcloned CNP cDNA inserts hybridized to mRNAs of approximately 2400 and approximately 2800 nucleotides (nts), and to a approximately 2500 nt mRNA from thymus. Several nonexpressing CNP cDNAs were identified by plaque hybridization, and the mRNA transcribed in vitro from one of these cDNAs (pCNP7) encoded a complete 46 kDa CNP polypeptide. Examination of the deduced amino acid sequence revealed an apparent homology to cAMP binding sites in several other proteins. A 373 bp segment from the 5' end of this pCNP7 hybridized only to the 2800 nt nervous system mRNAs, thus revealing that not all CNP mRNAs share the same 5'-ends. Genomic DNA blots probed with CNP cDNAs suggest that there is a single gene which can be alternatively spliced to produce the various mRNA transcripts in the nervous and lymphoid tissues.

2',3'-Cyclic Nucleotide 3'-Phosphodiesterase↗
PubMed1986

Small basic proteins of myelin from central and peripheral nervous systems are encoded by the same gene.

Peripheral nervous system (PNS) and central nervous system (CNS) rodent myelins, which are produced by different cell types, share common morphological and functional characteristics although their major integral membrane proteins are completely different. Both types of myelin however, contain sets of four myelin basic proteins (MBPs), which share similar immunochemical and electrophoretic properties. We have isolated and characterized cDNA clones corresponding to the rat mRNAs encoding the small MBPs (SMBPs) found in both CNS and PNS myelin. Sequence analysis of these clones indicate that SMBPs in both divisions of the nervous system are encoded by the same nucleotide sequences, which suggests that they are the products of the same gene expressed in both oligodendrocyte and Schwann cells. In dot-blot hybridization experiments with the CNS SMBP cDNA as a probe, it was shown that there is a 20-fold higher level of MBP mRNA in a CNS myelin fraction than in total brainstem mRNA. It also was found that in optic and sciatic nerves, which contain oligodendrocytes and Schwann cells respectively, there are higher levels (4-fold and 2-fold, respectively) of MBP mRNA than in brainstem. Blot-hybridization experiments showed that a probe derived from the coding region of the rat SMBP cDNA hybridizes to an homologous mRNA (approximately equal to 2.6 kilobases) present in human optic nerve, which is not detectable with a probe derived from the 3' untranslated region. This conservation of coding-region sequences is in accord with the highly homologous amino acid sequences reported for the MBPs in the two species.

Animals↗
PubMed1982

Synthesis and incorporation of myelin polypeptides into CNS myelin.

The distribution of newly synthesized proteolipid protein (PLP, 23 kdaltons) and myelin basic proteins (MBPs, 14-21.5 kdaltons) was determined in microsomal and myelin fractions prepared from the brainstems o1 10-30 d-old rats sacrificed at different times after an intracranial injection of 35S-methionine. Labeled MBPs were found in the myelin fraction 2 min after the injection, whereas PLP appeared first in the rough microsomal fraction and only after a lag of 30 min in the myelin fraction. Cell-free translation experiments using purified mRNAs demonstrated that PLP and MBPs are synthesized in bound and free polysomes, respectively. A mechanism involving the cotranslational insertion into the ER membrane and subsequent passage of the polypeptides through the Golgi apparatus is consistent with the lag observed in the appearance of the in vivo-labeled PLP in the myelin membrane. Newly synthesized PLP and MBPs are not proteolytically processed, because the primary translation products synthesized in vitro had the same electrophoretic mobility and N-terminal amino acid sequence as the mature PLP and MBP polypeptides. It was found that crude myelin fractions are highly enriched in mRNAs coding for the MBPs but not in mRNA coding for PLP. This suggests that whereas the bound polysomes synthesizing PLP are largely confined to the cell body, free polysomes synthesizing MBPs are concentrated in oligodendrocyte processes involved in myelination, which explains the immediate incorporation of MBPs into the developing myelin sheath.

Animals↗
PubMed1976

Centrifugal fibers to the eye in a nonavian vertebrate: source revealed by horseradish peroxidase studies.

A source of efferent fibers to the eye of snakes of the genus Thamnophis has been identified by the use of the retrograde transport of horseradish peroxidase. Cell bodies of the contralateral nucleus of the ventral supraoptic decussation accumulate horseradish peroxidase after intraocular but not intraorbital injections. Intraocular injections also result in anterograde transport of horseradish peroxidase to retinofugal axon terminals. Intraorbital injections result in accumulation of horseradish peroxidase in the cell bodies of the cranial nerve nuclei of extraocular muscles.

Animals↗