1,720,965 research outputs found
The molecular biology of desmosomes and hemidesmosomes: ?What's in a name?'
No full textDesmosomes are junctions involved in intercellular adhesion of epithelial cells and hemidesmosomes are junctions involved in adhesion of epithelia to basement membranes. Both are characterised at the ultrastructural level by dense cytoplasmic plaques which are linked to the intermediate filament cytoskeleton of the cells. The plaques strongly resemble each other suggesting a relationship between the two kinds of junctions, as implied by their names. Recent characterisation of the molecular components of the junctions shows they are, in fact, quite unrelated implying that structural similarity is fortuitous. The molecular biology raises many fascinating problems relating to their structure and function.<br/
A study of desmosomes in colorectal carcinoma
No full textDesmosomes are adhesive junctions of epithelial cells. Their expression may be altered or lost in carcinomas resulting in reduced cellular adhesiveness. The desmosomes of colorectal carcinomas have been studied by fluorescent antibody staining, immunoblotting and electromicroscopy. A series of 58 malignant specimens, comprised of primary tumours and metastases, were desmosome positive. There was no indication of a comparative reduction in desmosome expression that might give rise to reduced adhesiveness of tumour cells, although loss of polarised junctional distribution in poorly differentiated tumours might have such a consequence. Western blotting analysis of colorectal cancers and cultured carcinoma cells identified desmosomal polypeptides dp1 + 2, dg1 and dg2 + 3 with similar relative molecular weights to normal homologues. In addition, a polypeptide of 140,000 was recognised only in malignant epithelium by anti-dg2 + 3 antiserum. The significance of this polypeptide is not understood. Tumours and uninvolved epithelium were exposed to low extracellular [Ca2+] to test whether tumour desmosomes were of reduced stability. This caused much cellular degradation in tumours but some viable cell clumps possessed desmosomes resistant to disruption by low [Ca2+]. Desmosomes may thus have a positive role in metastasis by maintaining intercellular adhesion between metastasising cells.<br/
Regulation of desmocollin transcription in mouse preimplantation embryos
No full textThe molecular mechanisms regulating the biogenesis of the first desmosomes to form during mouse embryogenesis have been studied. A sensitive modification of a reverse transcriptase-cDNA amplification procedure has been used to detect transcripts of the desmosomal adhesive cadherin, desmocollin. Sequencing of cDNA amplification products confirmed that two splice variants, a and b, of the DSC2 gene are transcribed coordinately. Transcripts were identified in unfertilized eggs and cumulus cells and in cleavage stages up to the early 8-cell stage, were never detected in compact 8-cell embryos, but were evident again either from the 16-cell morula or very early blastocyst (approx 32-cells) stages onwards. These two phases of transcript detection indicate DSC2 is encoded by maternal and embryonic genomes. Previously, we have shown that desmocollin protein synthesis is undetectable in eggs and cleavage stages but initiates at the early blastocyst stage when desmocollin localises at, and appears to regulate assembly of, nascent desmosomes that form in the trophectoderm but not in the inner cell mass (Fleming, T. P., Garrod, D. R. and Elsmore, A. J. (1991), Development 112, 527–539). Maternal DSC2 mRNA is therefore not translated and presumably is inherited by blastomeres before complete degradation. Our results suggest, however, that initiation of embryonic DSC2 transcription regulates desmocollin protein expression and thereby desmosome formation. Moreover, data from blastocyst single cell analyses suggest that embryonic DSC2 transcription is specific to the trophectoderm lineage. Inhibition of E-cadherin-mediated cell-cell adhesion did not influence the timing of DSC2 embryonic transcription and protein expression. However, isolation and culture of inner cell masses induced an increase in the amount of DSC2 mRNA and protein detected. Taken together, these results suggest that the presence of a contact-free cell surface activates DSC2 transcription in the mouse early embryo. <br/
Size heterogeneity, phosphorylation and transmembrane organisation of desmosomal glycoproteins 2 and 3 (desmocollins) in MDCK cells
No full textMetabolic labelling with [35S]methionine and immunoprecipitation with specific antibodies to bovine desmosomal glycoproteins 2 and 3 (dg2 and dg3: desmocollins) reveals a triplet of polypeptides of Mr 115,000, 107,000 and 104,000 in MDCK cells. Tunicamycin treatment shows that this heterogeneity does not arise through differential N-linked glycosylation. Under conditions in which cells are actively forming desmosomes, the largest polypeptide, dg2, becomes phosphorylated on serine, but the two smaller polypeptides, dg3a and 3b, do not. Controlled trypsinisation of intact cells yields three membrane-protected fragments (Mr 28,000, 24,000 and 23,000) derived from these glycoproteins. The largest of these fragments is phosphorylated but the two smaller fragments are not. A monoclonal antibody to bovine dg2 and dg3 stains MDCK cells cytoplasmically. In immunoblotting of MDCK cells the monoclonal antibody recognises dg2 strongly and shows a weaker reaction with a band of lower Mr corresponding to dg3a. It also recognises the immunoprecipitated 28,000 Mr fragment from trypsinised cells and a smaller fragment of 24,000 Mr. The simplest interpretation of these data is that all three glycoproteins have a transmembrane configuration with a single membrane-spanning domain, and show heterogeneity of size and phosphorylation in their cytoplasmic domains. The data are discussed in relation to the known structures of some cell adhesion molecules. Questions about the relative roles and distributions of the different polypeptides in desmosomal organisation are raised. <br/
Cloning, sequence and expression patterns of mouse desmocollin 2 (DSC 2): a cadherin-like adhesion molecule
No full textDesmocollins are cadherin-like adhesion molecules of desmosomes. We have determined the full cDNA sequence of a murine desmocollin, the homologue of human and bovine type 2 desmocollins (DSC2), and studied its tissue distribution and expression in stratified epithelia. An 8.5 day mouse embryo cDNA library was screened yielding overlapping clones which encoded the mouse DSC2. This gene has an open reading frame of 2710 base pairs (bp) encoding a polypeptide of 902 amino acids (aa). The polypeptide comprises a signal peptide, a precursor peptide, and a mature protein of 766 aa having an extracellular domain of 549 aa, a single transmembrane domain and a cytoplasmic domain of 184 aa. Like other desmocollins, murine DSC2 has two products, Dsc2a and Dsc2b, produced by alternative splicing of a 46 bp exon which encodes 11 COOH-terminal aa followed by an in-frame stop codon. Inclusion of this exon forms Dsc2b which is 54 aa shorter than Dsc2a. Mouse Dsc2a shows 75.7% amino acid identity to human and 63.3% identity to bovine Dsc2a. The mouse desmocollin is also homologous to the cadherins; 32.2% to the most closely related typical cadherin, human N-cadherin. DSC2 is ubiquitously expressed in epithelial tissues and the heart of adult mice and from the blastocyst stage of development. In situ hybridization shows that the gene is most strongly expressed suprabasally in stratified epithelia, similar to the expression of bovine DSC2.<br/
Desmosomal glycoproteins 2 and 3 (desmocollins) show N-terminal similarity to calcium-dependent cell-cell adhesion molecules
No full textThe N-terminal sequence of a mixture of desmosomal glycoproteins 2 and 3 (dg2/3, desmocollins) from bovine nasal epidermis, prepared by electro-elution from polyacrylamide gels, was determined by solid-phase Edman degradation. A sequence of 23 amino acids was obtained. This showed 43% identity with that of the N terminus of the calcium-dependent cell adhesion molecule, N-cadherin. A lesser degree of identity with other members of the cadherin-uvomorulin-L-CAM family was also found. In order to confirm that the sequence was derived from the dg2/3 molecules a rabbit antiserum was raised against a synthetic peptide corresponding to the sequence, conjugated to keyhole limpet haemocyanin (KLH). The antiserum obtained showed high (titre) activity against both the peptide and KLH in ELISA. Each activity could be specifically adsorbed with the appropriate ligand. The antiserum reacted specifically with both dg2 and dg3 of bovine nasal epidermis on immunoblots, this binding was blocked by the N-terminal peptide but was unaffected by KLH. The identity of dg2 and -3 in these preparations was confirmed by immunoblotting with two monoclonal antibodies and one polyclonal antiserum raised against the whole molecules. The N-terminal peptide antiserum was shown to bind to the intercellular space of desmosome profiles by immunoelectron microscopy on ultra-thin frozen sections. One of the two monoclonal antibodies (07-4D) also reacted with the desmosomal intercellular space. dg2 and -3 were shown by Staphylococcus aureus V8 protease digestion to have identical one-dimensional peptide maps. Both the N-terminal antiserum and 07-4D reacted with a V8 fragment of 19,000 Mr derived from dg2 and dg3
Behavioural plasticity in developing animals.
No full textIn: Development in the nervous system, Series Editor: Garrod, D.R. and Feldman, J.D.Onderzoeksbibliografie Frank OdbergHerkomst: Onderzoeksbibliografie van em. prof. dr. Frank O. Ödberg, verbonden aan de Vakgroep Voeding, Genetica en Ethologie van de Faculteit Diergeneeskund
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Cloning and sequence analysis of desmosomal glycoprotein 2 and 3 cDNAs: cadherin-like desmosomal adhesion molecules with heterogeneous cytoplasmic domains
Get PDFDesmosomal glycoproteins 2 and 3 (dg2 and 3) or desmocollins have been implicated in desmosome adhesion. We have obtained a 5.0-kb-long clone for dg3 from a bovine nasal epidermal lambda gt11 cDNA library. Sequence analysis of this clone reveals an open reading frame of 2,517 bases encoding a polypeptide of 839 amino acids. The sequence consists of a signal peptide of 28 amino acids, a precursor sequence of 104 amino acids, and a mature protein of 707 amino acids. The latter has the characteristics of a transmembrane glycoprotein with an extracellular domain of 550 amino acids and a cytoplasmic domain of 122 amino acids. The sequence of a partial clone from the same library shows that dg2 has an alternative COOH terminus that is extended by 54 amino acids. Genomic DNA sequence data show that this arises by splicing out of a 46-bp exon that encodes the COOH-terminal 11 amino acids of dg3 and contains an in-frame stop codon. The extracellular domain of dg3 shows 39.4% protein sequence identity with bovine N-cadherin and 28.4% identity with the other major desmosomal glycoprotein, dg1, or desmoglein. The cytoplasmic domain of dg3 and the partial cytoplasmic domain of dg2 show 23 and 24% identity with bovine N-cadherin, respectively. The results support our previous model for the transmembrane organization of dg2 and 3 (Parrish, E.P., J.E. Marston, D.L. Mattey, H.R. Measures, R. Venning, and D.R. Garrod. 1990. J. Cell Sci. 96:239-248; Holton, J.L., T.P. Kenny, P.K. Legan, J.E. Collins, J.N. Keen, R. Sharma, and D.R. Garrod. 1990. J. Cell Sci. 97:239-246). They suggest that these glycoproteins are specialized for calcium-dependent adhesion in their extracellular domains and, cytoplasmically, for the molecular interactions involved in desmosome plaque formation. Moreover this represents the first example of alternative splicing within the cadherin family of cell adhesion molecules. <br/
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