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W W Franke

Publications and source records attributed to W W Franke.

At least 19 recordsLinked to original sources
PubMed1992

Identification of a nonapeptide motif in the vimentin head domain involved in intermediate filament assembly.

The assembly of soluble vimentin subunits into intermediate filaments (IFs) is dependent on information located in the amino-terminal domain. Using site-directed mutagenesis of a Xenopus laevis vimentin cDNA and an Escherichia coli production system to obtain pure mutated protein, we have identified, in the head domain, a nine amino acid motif (SSYRRIFGG), evolutionarily conserved from amphibia to man, which plays an important role in the orderly formation of IFs. Exchanges in the central di-arginine and in the two aromatic residues interfere with IF assembly of vimentin in vitro: on assembly under standard assembly conditions (160 mM-NaCl) most of the protein is included in dense aggregates, with a variable and minor proportion of IFs, whereas at lower ionic concentrations short and incomplete IF-like structures are formed. The deletion of the whole motif results in a protein that under standard assembly conditions (e.g. 160 mM-NaCl) predominantly and rapidly precipitates into large aggregates of non-IF material, whereas at lower ionic strength (e.g. 50 mM-NaCl) both IFs and dense aggregates are formed simultaneously. Our results show that the mutated protein can assume different forms at the same time and under the same conditions. This motif alone is insufficient for the formation of normal IFs as demonstrated by a mutant in which the motif has been brought closer to the alpha-helical rod domain by deletion of 55 internal amino acid residues. Corresponding observations have been made, by immunofluorescence microscopy, upon transfection of cultured epithelial cells lacking vimentin IFs. The importance of the head domain motif for the assembly and higher-order arrangement of IFs is discussed.

3T3 Cells↗
PubMed1992

Ubiquitous soluble Mg(2+)-ATPase complex. A structural study.

We have performed a detailed structural analysis of the soluble Mg(2+)-ATPase complex purified from Xenopus laevis ovary, which is an abundant and ubiquitous homo-oligomeric protein complex located in the nucleus and in the cytoplasm, belonging to a novel multigene-family of putative Mg(2+)-ATPases. Enzyme activity staining after non-denaturing polyacrylamide gel electrophoresis revealed that Mg(2+)-ATPase activity of the native protein is dependent on oligomerization and could not be detected in dissociated subunits. For the native protein a sedimentation coefficient of 15.3 S and a corresponding relative molecular mass of 612,000 was determined by analytical ultracentrifugation and a relative molecular mass of 590,000 was estimated from scanning transmission electron microscopy, supporting our previous conclusion that the oligomer comprises six 97,000 Mr subunits. Conventional electron microscopy of negatively stained specimens revealed the Mg(2+)-ATPase complex to be a hexagonal molecule in its favoured "end-on" projection and a double-banded molecule in its "side-on" projection (approx. 12 nm diameter; approx. 9 nm height). In addition, dimerized complexes could be observed in negatively stained specimens, yielding pronounced hexameric images and four-banded images in their end-on and side-on orientations, respectively (approx. 12 nm diameter; approx. 18.5 nm height). Two-dimensional (2D = mono-molecular) crystals have been produced from the dimerized complexes by the negative staining carbon film technique. Hexagonal crystals with a p6 plane group symmetry were obtained from molecules in their end-on orientation and longitudinal arrays with a p2 symmetry from complexes in their side-on orientation. A low-resolution molecular model of the native protein, derived from averages of these two 2D crystals, is presented. From our results we propose oligomerization as an inherent structural principle of organization for this whole newly defined Mg(2+)-ATPase multigene-family, that includes such seemingly diverse functionally defined proteins as mammalian and yeast "vesicle fusion" and "peroxisome assembly" proteins and the product of the yeast cell cycle gene CDC48.

Animals↗
PubMed1992

Sequence analysis of cytoplasmic mRNA-binding proteins of Xenopus oocytes identifies a family of RNA-binding proteins.

Storage of maternal mRNAs as nontranslated ribonucleoprotein (RNP) complexes is an adaptive strategy in various vertebrate and invertebrate oocytes, for rapid translational recruitment during embryonic development. Previously, we showed that Xenopus laevis oocytes have a soluble cytoplasmic pool of mRNA-binding proteins and particles competent for messenger RNP assembly in vitro. Here we report the isolation of cDNAs for the most abundant messenger RNPs, the 54- and 56-kDa polypeptide (p54/p56) components of the approximately 6S mRNA-binding particle, from an ovarian expression library. The nucleotide sequence of p56 cDNA is almost identical to that recently reported for the putative Xenopus transcription factor FRG Y2. p54 and p56 are highly homologous and are smaller than expected by SDS/PAGE (36 kDa and 37 kDa) due to anomalous electrophoretic mobility. They lack the "RNP consensus motif" but contain four arginine-rich "basic/aromatic islands" that are similar to the RNA-binding domain of bacteriophage mRNA antiterminator proteins and of tat protein of human immunodeficiency virus. The basic/aromatic regions and a second conspicuous 100-amino acid "domain C" of p54 and p56 are conserved in the following DNA-binding proteins: human proteins dpbA, dpbB, and YB-1, rat protein EFIA, and Xenopus protein FRG Y1, all reported to bind to DNA; domain C is homologous to the major Escherichia coli cold-stress-response protein reportedly involved in translational control. Antibodies raised against a peptide of domain C have identified similar proteins in Xenopus somatic cells and in some mammalian cells and tissues. We conclude that p54 and p56 define a family of RNA-binding proteins, at least some of which may be involved in translational regulation.

Amino Acid Sequence↗
PubMed1992

Complexity and expression patterns of the desmosomal cadherins.

Desmosomes are intercellular junctions that contain two major kinds of transmembrane glycoproteins, desmoglein and desmocollins I and II, involved in cell-cell adhesion. Recent sequence analyses have shown that both desmosomal glycoproteins belong to the larger cadherin family of cell adhesion molecules, in which they represent two different subgroups characterized by their specific sequence and topogenesis. In analyses of cDNA sequences and Northern blot experiments we have now found that both desmoglein and desmocollins are not unique gene products but occur in different subtypes produced from different genes. Comparison of the complete amino acid sequences of type 1 and type 2 desmocollins and of two desmoglein subtypes shows considerable divergence. While the desmoglein genes can be differentially expressed in different cell types, both type 1 and type 2 desmocollins can coexist in the same cells of certain stratified epithelia as shown by in situ hybridization. We conclude that the cadherin composition of desmosomes is much more complex than assumed and can differ in the various epithelia.

Amino Acid Sequence↗
PubMed1992

Characterization of human cytokeratin 2, an epidermal cytoskeletal protein synthesized late during differentiation.

Among the more than 30 different human proteins of the cytokeratin (CK) group of intermediate filament (IF) proteins, the significance of the epidermal polypeptide CK 2 (Moll et al., 1982, Cell 31, 11-24) has been repeatedly questioned in the literature. Here, we show, by in vitro translation and protein gel electrophoresis, that human epidermis from various body sites does indeed contain relatively large amounts of mRNA encoding a distinct polypeptide comigrating with native epidermal CK 2. We also report the isolation of a cDNA clone encoding the complete sequence of CK 2, which is a type II CK different from--but related to--epidermal CKs 1 and 5 on the one hand and corneal CK 3 on the other. The mRNA of approximately 2.6 kb encodes a polypeptide of 645 amino acids and M(r) 65,852, in good agreement with the value of 65.5 kDa previously estimated from gel electrophoresis. This human CK, the largest so far known, displays several features typical of CKs of stratified epithelia, including numerous repeats of glycine-rich tetrapeptides in the head and tail domains. Northern blot and in situ hybridizations have shown that CK 2 is expressed strictly suprabasally, usually starting in the third or fourth cell layer of epidermis, and this was confirmed at the protein level by immunohistochemistry using CK 2-specific antibodies. The protein has been detected as a regular epidermal component in skin samples from different body sites, albeit as a minor CK in "soft skin" (e.g., breast nipple, penile shaft, axilla), but not in foreskin epithelium and in other epithelia, in squamous metaplasias and carcinomas, or in cultured cell lines derived therefrom. We propose that CK 2 is a late cytoskeletal IF addition synthesized during maturation of epidermal keratinocytes which probably contributes to terminal cornification.

Amino Acid Sequence↗
PubMed1992

Suprabasal marker proteins distinguishing keratinizing squamous epithelia: cytokeratin 2 polypeptides of oral masticatory epithelium and epidermis are different.

Terminal differentiation of squamous epithelia is usually characterized by the synthesis of a subset of cytokeratins (CKs) in suprabasal cell layers which become major components of the intermediate filament (IF) bundle cytoskeleton of the maturing cells. We have examined the significance, molecular nature and pattern of synthesis of the elusive human CK 2 by analyzing mRNAs from certain stratified epithelia, using in vitro translation, cDNA cloning. Northern blotting and in situ hybridization. We show that genuine polypeptides with the typical gel electrophoretic mobility of CK 2 exist but that the CK 2 present in the masticatory epithelia of hard palate and gingiva (CK 2p) differs from that found in epidermis (CK 2e) by its amino acid sequence and is encoded by a different gene. The two CKs 2 show only limited sequence homology (71% identical amino acid positions in the rod domain), and the oral CK 2p is more closely related to the corneal CK 3 (86%), as is also indicated by the cross-reaction of monoclonal antibody AE5. By in situ hybridization and immunocytochemistry, we further show that both CK 2e and CK 2p are expressed only in suprabasal cell layers of the specific epithelia where they can accumulate to represent major cytoskeletal proteins. We discuss this tissue-type specificity of CK 2 synthesis in otherwise morphologically and biochemically similar epithelia in relation to differences of IF appearance and packing in upper strata between epidermal and masticatory epithelia as well as to tissue formation and differentiation during development.

Amino Acid Sequence↗
PubMed1992

Identification of plakoglobin in oocytes and early embryos of Xenopus laevis: maternal expression of a gene encoding a junctional plaque protein.

We have isolated a cDNA encoding the junctional plaque protein plakoglobin of Xenopus laevis and determined its amino acid sequence. Comparisons with sequences of related proteins of the same and other species revealed that in Xenopus plakoglobin and beta-catenin are two different proteins, encoded by separate genes, that both genes are expressed in embryogenesis, and that the amphibian plakoglobin is more closely related to the human plakoglobin than to beta-catenin of the same species. Using this cDNA as a probe, we also show that plakoglobin mRNA is produced and stored in Xenopus oocytes and eggs. We discuss the possibility that the maternal pool of this junctional protein contributes to the junctional structures connecting the oocyte with the follicle epithelium and to the rapid formation of desmosomes and other plaque-bearing junctions in pregastrulation embryogenesis.

Amino Acid Sequence↗
PubMed1992

Characterization of the human gene encoding cytokeratin 17 and its expression pattern.

Among the members of the cytokeratin (CK) subfamily of intermediate filament (IF) proteins, CK 17 is remarkable as it is normally expressed in the basal cells of complex epithelia but not in stratified or simple epithelia. Because of its unusual expression pattern in normal and diseased states and because of the potential importance of CK 17 in tumor diagnosis, we have characterized the gene(s) and its cDNA-derived amino acid sequence. A cDNA clone encoding CK 17 was isolated from a HeLa cDNA library and used for the determination of the amino acid sequence, for studies of expression and for the screening of human genomic libraries. A number of lambda phage clones were isolated that covered three distinct, non-contiguous gene regions. Only one of these loci contains the functional CK 17 gene which is located only approximately 5 kbp 5'-upstream of the CK 16 gene, whereas the other two contain unprocessed CK 17 pseudogenes. Each of these genes is part of a larger CK type I gene locus the arrangement of which suggests that these genes and pseudogenes have arisen during evolution by duplication events comprising whole multigene loci. The functional CK 17 gene differs from the pseudogenes by the extent of methylation of certain DNA sequences in the 5'-upstream region. The 5 kbp CK 17 gene with 8 exons and 7 introns encodes a polypeptide of 432 amino acids with a calculated molecular weight of 48,000. Using S1-nuclease protection assays and RNAs from several cell lines we identified a single transcriptional start point 26 nucleotides down-stream from a TATA box element. Northern blot hybridization experiments showed a restricted pattern of CK 17 gene expression, supporting the notion that CK 17 synthesis is essentially regulated at the transcriptional level. From these findings and from immunohistological observations, CK 17 synthesis seems to be a marker of basal cell differentiation in complex epithelia and therefore indicative of a certain type of epithelial "stem cells".

Amino Acid Sequence↗
PubMed1992

An amphicrine pancreatic cell line: AR42J cells combine exocrine and neuroendocrine properties.

The permanent cell culture line AR42J, derived from a rat pancreatic acinar carcinoma, is widely used for functional studies of exocrine pancreatic acinar cells. We now present evidence that these cells are amphicrine in that they contain zymogen granules as well as small (40-80 nm) neuroendocrine (NE) vesicles and typical neurotransmitters. Using the small NE vesicle-specific markers synaptophysin and "protein S.V.2", including synaptophysin cDNA probes, we have found that AR42J cells synthesize these proteins and contain vesicles harboring these proteins with biophysical properties similar to those of small NE vesicles. NE properties of these cells are further indicated by the presence of considerable amounts of stored amino acids (gamma-aminobutyric acid (GABA), glycine, glutamate) and by the presence of the GABA-synthesizing enzyme, glutamic acid decarboxylase. Finally, intermediate filament (IF) protein typing showed only cytokeratins 8 and 18, indicating that AR42J cells possess an IF protein complement indistinguishable from that of acinar and islet cells. Our results document the unusual case of a permanent cell line with combined exocrine and neuroendocrine properties that may be indicative of a derivation from a cell with multipotential character.

Animals↗
PubMed1992

Cytokeratin 20 in human carcinomas. A new histodiagnostic marker detected by monoclonal antibodies.

The authors have recently identified a new cytokeratin (CK) polypeptide, CK 20, whose expression is almost entirely confined to the gastric and intestinal epithelium, urothelium, and Merkel cells. Seven monoclonal antibodies (MAbs) specific for CK 20 were raised and characterized by applying immunoblotting and immunocytochemical screening. All of them reacted on frozen tissue sections. A further MAb, IT-Ks20.8, recognized CK 20 in sections of formalin-fixed, paraffin-embedded tissue samples. A total of 711 cases of primary and metastatic cancer, mostly carcinomas, were analyzed immunohistochemically for CK-20 expression, using CK-20 specific guinea-pig antibodies and MAbs. The expression spectrum of CK 20 in carcinomas resembled that seen in the corresponding normal epithelia of origin. CK-20 positivity was seen in the vast majority of adenocarcinomas of the colon (89/93 cases), mucinous ovarian tumors, transitional-cell and Merkel-cell carcinomas and frequently also in adenocarcinomas of the stomach, bile system, and pancreas. Most squamous cell carcinomas in general and most adenocarcinomas from other sites (breast, lung, endometrium), nonmucinous tumors of the ovary, and small-cell lung carcinomas were essentially or completely negative. The authors propose to use CK 20 as a diagnostic marker valuable in distinguishing different types of carcinomas, notably when presenting as metastases.

Animals↗
PubMed1992

Assembly of a tail-less mutant of the intermediate filament protein, vimentin, in vitro and in vivo.

Recent reports on the possible contribution of the non-alpha-helical carboxy-terminal domain ("tail") of type III intermediate filament (IF) proteins to IF assembly have been controversial. To examine the importance and role of this domain, we have therefore engineered a Xenopus laevis vimentin cDNA to code for a tail-less polypeptide and have used it in combination with prokaryotic and eukaryotic expression systems. Here we show that tail-less vimentin, isolated from transfected bacteria (Escherichia coli), when used for assembly in vitro, forms normal-looking, loosely packed IFs. By viscometry we demonstrate that this tail-less vimentin assembles at an even higher rate and into longer IFs than wild-type vimentin. In vivo, i.e., by forced expression in transfected type III IF-free cultured epithelial cells, tail-less vimentin was also recovered in short fibrillar structures, in rodlets and in small as well as large spheroidal aggregates ("granules") that did not reveal any IF substructure. Surprisingly, however, spheroidal aggregate structures formed from the tail-deleted vimentin, were seen not only in the cytoplasm but also in the nucleus, indicating a role of the tail in higher order organization and compartmentalization of the vimentin IF system.

Animals↗
PubMed1991

Isolation and characterization of hemidesmosomes from bovine corneal epithelial cells.

The hemidesmosome (HD) is a specialized cell-to-substratum junction of stratified and complex epithelia which is characterized by a cytoplasmic plaque to which intermediate filaments (IFs) are anchored. To identify and characterize HD constituents systematically, we have developed a procedure to isolate and fractionate HDs. When bovine corneal epithelium is peeled off from the extracellular matrix stroma, HDs attached to the basal lamina are left behind, together with tufts of cytokeratin IFs attached to the cytoplasmic HD plaques. After rinsing these residual basal cell elements with EDTA, the HDs could be mechanically detached from the stroma and collected by centrifugation. The fraction obtained was examined biochemically and electron microscopically, showing enrichment of HD structures as well as of a prominent 230-kDa polypeptide, the "pemphigoid antigen" known to be located in the HD plaque. In addition, the HD fraction revealed, besides residual amounts of corneal cytokeratins, major polypeptides of Mr 120, 180, 200, 230, and 480 kDa, of which the first three appeared to be glycoproteins. Using the isolated HDs for immunization, we prepared monoclonal antibodies specific for the 230- and 180-kDa polypeptides, respectively, and showed that both were exclusively located in HDs. This method for isolating HDs and the availability of antibodies to HD proteins will be useful in studies of the molecular organization of HDs and make HD research independent from human autoimmune antibodies.

Animals↗
PubMed1991

Complexity of expression of intermediate filament proteins, including glial filament protein, in endometrial and ovarian adenocarcinomas.

The expression patterns of intermediate filament proteins of primary and metastatic endometrial (n = 18) and ovarian (n = 24) adenocarcinomas were analyzed by immunocytochemistry using a panel of specific antibodies and by gel electrophoresis of cytoskeletal preparations, followed by immunoblotting. All cells of all endometrial adenocarcinomas studied contained the "simple epithelial"-type cytokeratins (CKs) 8, 18, and (mostly) 19, with variable numbers of cells also positive for CK 7 and vimentin. In addition, most of these tumors contained individual cells or groups of cells that were positive for the stratification-related CKs 4, 5, 6, 13, 14, and 17. The latter CKs were often associated with squamous cell foci, but were also found in some single (nonsquamous) tumor cells, indicative of early stages of squamous cell differentiation. Ovarian carcinomas of various histologic types and grades contained predominantly CKs 7, 8, 18, and 19. Serous, endometrioid, and anaplastic tumors, but not mucinous and clear cell tumors, also contained minor amounts of stratification-related CKs in variable combinations, mostly including CK 4. In all tumor types except mucinous tumors, vimentin was consistently detected in variable proportions of tumor cells which, however, were rather low in anaplastic carcinomas. Surprisingly, glial filament protein was detected in a minor proportion (< or = 20%) of tumor cells in seven of 14 serous and endometrioid ovarian carcinomas and in three of 18 endometrial carcinomas. These different intermediate filament expression patterns of müllerian duct-type carcinomas, only partly related to the morphologic appearance of the specific type of tumor, might reflect the multipotentiality of differentiation of müllerian duct-derived epithelia. Cytoskeletal features of potential diagnostic value, especially in metastatic carcinomas, are discussed.

Adenocarcinoma↗
PubMed1991

Different forms of soluble cytoplasmic mRNA binding proteins and particles in Xenopus laevis oocytes and embryos.

To gain insight into the mechanisms involved in the formation of maternally stored mRNPs during Xenopus laevis development, we searched for soluble cytoplasmic proteins of the oocyte that are able to selectively bind mRNAs, using as substrate radiolabeled mRNA. In vitro mRNP assembly in solution was followed by UV-cross-linking and RNase digestion, resulting in covalent tagging of polypeptides by nucleotide transfer. Five polypeptides of approximately 54, 56 60, 70, and 100 kD (p54, p56, p60, p70, and p100) have been found to selectively bind mRNA and assemble into mRNPs. These polypeptides, which correspond to previously described native mRNP components, occur in three different particle classes of approximately 4.5S, approximately 6S, and approximately 15S, as also determined by their reactions with antibodies against p54 and p56. Whereas the approximately 4.5S class contains p42, p60, and p70, probably each in the form of individual molecules or small complexes, the approximately 6S particles appears to consist only of p54 and p56, which occur in a near-stoichiometric ratio suggestive of a heterodimer complex. The approximately 15S particles contain, in addition to p54 and p56, p60 and p100 and this is the single occurring form of RNA-binding p100. We have also observed changes in the in vitro mRNA binding properties of these polypeptides during oogenesis and early embryonic development, in relation to their phosphorylation state and to the activity of an approximately 15S particle-associated protein kinase, suggesting that these proteins are involved in the developmental translational regulation of maternal mRNAs.

Animals↗
PubMed1991

Endocytosis of junctional cadherins in bovine kidney epithelial (MDBK) cells cultured in low Ca2+ ion medium.

The release of intercellular contacts in MDBK cells, initiated by the depletion of Ca2+ ions from the culture medium, results in the endocytotic uptake of membrane vesicles containing specific membrane constituents of the zonula adhaerens (ZA). During this process the junction-derived, endocytosed vesicles remain associated with the ZA plaque components, while the plaque and its attached actin filaments retract as a whole in a ring-like fashion from the plasma membrane, often accumulating, usually in fragments, in the juxtanuclear cytoplasm. Double-label immunofluorescence microscopy with antiplakoglobin and antivinculin has indicated that both plaque proteins colocalize with the hallmark membrane glycoprotein of this junction type, E-cadherin (uvomorulin). When HRP used as a fluid phase marker is applied to the culture medium, simultaneously with the Ca2+ ion-chelator EGTA, numerous HRP-positive vesicles are found in close association with the dislocated plaque material, suggesting that the HRP is contained in the vesicles formed upon EGTA-induced junction splitting. Immunoelectron microscopy with various cadherin-specific antibodies revealed vesicle-associated labeling, confirming the derivation of these plaque-associated vesicles from the ZA. As the desmosome-specific cadherin, desmoglein, is recovered in another type of junction-derived vesicle, which is characterized by its association with a desmoplakin-plaque, we conclude that the membrane domains of both kinds of junction are endocytosed during Ca2+ depletion but stay in different vesicle populations, emphasizing the selective interaction of the specific cadherins with their respective plaque and filament partners.

Actins↗
PubMed1991

Intermediate filaments formed de novo from tail-less cytokeratins in the cytoplasm and in the nucleus.

The roles of the different molecular domains of intermediate filament (IF) proteins in the assembly and higher order organization of IF structures have recently been studied by various groups but with partially controversial results. To examine the requirement of the aminoterminal (head) and the carboxyterminal (tail) domain of cytokeratins (CKs) for de novo IF formation in the living cell, we have constructed cDNAs coding for intact as well as head- and/or tail-less human CKs 8 and 18 and the naturally tail-less human CK 19, all under the control of the human beta-actin promoter. After transient and stable transfections of mouse 3T3-L1 cells, which are devoid of any CKs, we have studied, with such constructs, the resulting gene products by gel electrophoresis and immunolocalization techniques. By light and electron microscopy we show that extended cytoplasmic IF meshworks are formed from pairs of the type II CK 8 with the type I CKs 18 or 19 as well as from pairs of tail-less CK 8 with tail-less CKs 18 or 19 in the transfected cells, proving that the absence of the tail domain in both types of CKs does not prevent the de novo formation of regular IFs. Most surprisingly, however, we have observed spectacular alterations in the nucleocytoplasmic distribution of the IFs formed from tail-less CKs. In many of the transfected cells, a large part, or all, of the detectable CKs was found to occur in extensive IF bundles in the nucleoplasm. Intranuclear accumulations of CK deposits, however mostly nonfibrillar, were also observed when the cells had been transfected with cDNAs encoding tail-less CKs also lacking their head domains, whereas CKs deleted only in the head domain were found exclusively in the cytoplasm. The specific domain requirements for the assembly of cytoplasmic IF bundles are discussed and possible mechanisms of intranuclear accumulation of IFs are proposed.

3T3 Cells↗
PubMed1991

Amino acid sequence of bovine muzzle epithelial desmocollin derived from cloned cDNA: a novel subtype of desmosomal cadherins.

Desmosomes are cell-type-specific intercellular junctions found in epithelium, myocardium and certain other tissues. They consist of assemblies of molecules involved in the adhesion of specific cell types and in the anchorage of cell-type-specific cytoskeletal elements, the intermediate-size filaments, to the plasma membrane. To explore the individual desmosomal components and their functions we have isolated DNA clones encoding the desmosomal glycoprotein, desmocollin, using antibodies and a cDNA expression library from bovine muzzle epithelium. The cDNA-deduced amino-acid sequence of desmocollin (presently we cannot decide to which of the two desmocollins, DC I or DC II, this clone relates) defines a polypeptide with a calculated molecular weight of 85,000, with a single candidate sequence of 24 amino acids sufficiently long for a transmembrane arrangement, and an extracellular aminoterminal portion of 561 amino acid residues, compared to a cytoplasmic part of only 176 amino acids. Amino acid sequence comparisons have revealed that desmocollin is highly homologous to members of the cadherin family of cell adhesion molecules, including the previously sequenced desmoglein, another desmosome-specific cadherin. Using riboprobes derived from cDNAs for Northern-blot analyses, we have identified an mRNA of approximately 6 kb in stratified epithelia such as muzzle epithelium and tongue mucosa but not in two epithelial cell culture lines containing desmosomes and desmoplakins. The difference may indicate drastic differences in mRNA concentration or the existence of cell-type-specific desmocollin subforms. The molecular topology of desmocollin(s) is discussed in relation to possible functions of the individual molecular domains.

Amino Acid Sequence↗