Striate palmoplantar keratoderma arising from desmoplakin and desmoglein 1 mutations is associated with contrasting perturbations of desmosomes and the keratin filament network.

BACKGROUND: Several hereditary human diseases are now known to be caused by distinct mutations in genes encoding various desmosome components. Although the effects of some of these mutant genes have been analysed by targeted disruption experiments in mouse models, little is known about the cell and tissue changes in affected human patients. OBJECTIVES: To investigate the effects of heterozygous nonsense mutations in desmoplakin (Dp) and desmoglein (Dsg) 1 which cause the autosomal dominant disorder striate palmoplantar keratoderma (SPPK), focusing on changes in desmosome structure and composition and the associated keratin intermediate filament (KIF) network in palm skin, and in cultured keratinocytes generated from the same site. METHODS: We analysed palm and nonpalm skin sections from four SPPK patients with Dp mutations and one patient with a Dsg1 mutation with respect to tissue and subcellular morphologies, and correlated the in vivo and in vitro findings. RESULTS: Using electron microscopy, we found abnormalities of desmosomes and cell-cell adhesion in the suprabasal layers in the epidermis from patients with both Dsg1- and Dp-associated SPPK. These changes were more advanced in skin from patients with Dp mutations. Both Dp and Dsg1 mutations were accompanied by significantly reduced numbers of desmosomes in the suprabasal layers, while decreased desmosome size was evident only in Dsg1-associated SPPK. Confocal microscopy analysis showed marked differences in the expression of keratins and of desmosome components, both between the two types of SPPK, and between SPPK and normal skin. The expression of keratins K5, K14 and K10 was reduced in Dsg1-associated SPPK skin, whereas perinuclear aggregation of keratin filaments was more evident in Dp-associated SPPK. In both types of SPPK upregulation of K16 was pronounced and involucrin labelling was abnormal. CONCLUSIONS: Mutations in Dp and Dsg1 genes causing SPPK may be associated with perturbations in epidermal differentiation accompanied by a marked disruption of several components of the epidermal scaffold including desmosomes and the KIF network.

Parasite plastids: maintenance and functions.

Malaria and related parasites retain a vestigial, but biosynthetically active, plastid organelle acquired far back in evolution from a red algal cell. The organelle appears to be essential for parasite transmission from cell to cell and carries the smallest known plastid genome. Why has this genome been retained? The genes it carries seem to be dedicated to the expression of just two "housekeeping" genes. We speculate that one of these, called ycf24 in plants and sufB in bacteria, is tied to an essential "dark" reaction of the organelle--fatty acid biosynthesis. "Ball-park" clues to the function of bacterial suf genes have emerged only recently and point to the areas of iron homeostasis, [Fe-S] cluster formation and oxidative stress. We present experimental evidence for a physical interaction between SufB and its putative partner SufC (ycf16). In both malaria and plants, SufC is encoded in the nucleus and specifies an ATPase that is imported into the plastid.

Spectrum of dominant mutations in the desmosomal cadherin desmoglein 1, causing the skin disease striate palmoplantar keratoderma.

The adhesive proteins of the desmosome type of cell junction consist of two types of cadherin found exclusively in that structure, the desmogleins and desmocollins, coded by two closely linked loci on human chromosome 18q12.1. Recently we have identified a mutation in the DSG1 gene coding for desmoglein 1 as the cause of the autosomal dominant skin disease striate palmoplantar keratoderma (SPPK) in which affected individuals have marked hyperkeratotic bands on the palms and soles. In the present study we present the complete exon-intron structure of the DSG1 gene, which occupies approximately 43 kb, and intron primers sufficient to amplify all the exons. Using these we have analysed the mutational changes in this gene in five further cases of SPPK. All were heterozygotic mutations in the extracellular domain leading to a truncated protein, due either to an addition or deletion of a single base, or a base change resulting in a stop codon. Three mutations were in exon 9 and one in exon 11, both of which code for part of the third and fourth extracellular domains, and one was in exon 2 coding for part of the prosequence of this processed protein. This latter mutation thus results in the mutant allele synthesising only 25 amino acid residues of the prosequence of the protein so that this is effectively a null mutation implying that dominance in the case of this mutation was caused by haploinsufficiency. The most severe consequences of SPPK mutations are in regions of the body where pressure and abrasion are greatest and where desmosome function is most necessary. SPPK therefore provides a very sensitive measure of desmosomal function.

The regulatory region of the human desmocollin 3 promoter forms a DNA four-way junction.

Adhesion between desmosomal junctions is mediated by structural proteins of the cadherin family, viz. three desmocollins (DSC) and three desmogleins (DSG). Promoter and primer extension analysis of human DSC3 showed a TATA-less sequence initiating transcription via a cluster of sites upstream of the coding region. Deletion analysis of 1 kb of the promoter showed that expression is regulated between --303 and --203 bp upstream of the start-site of translation. Tertiary structure analysis of this cis-active region (cis 1) revealed a potential DNA 4-way junction which is notably G/C-rich in sequence. PAGE analysis of this region identified four differently migrating forms of the DNA. Structure-specific cleavage of the DNA with bacteriophage T7 endonuclease I showed the slowest migrating form to be either an extended/cruciform or stacked-X 4-way junction. DNA-binding, gel retardation assays of the cis 1 region showed distinct DNA-protein complexes and by competition experiments and using purified junction DNA we show that one of these complexes bound with both sequence and structure specificity to the 4-way junction DNA.

Extracellularly truncated desmoglein 1 compromises desmosomes in MDCK cells.

The formation and stability of epithelial tissue involves cell adhesion and the connection of the intermediate filaments of contiguous cells, mediated by desmosomes. The cadherin family members Desmocollins (Dsc) and Desmogleins (Dsg) mediate desmosome extracellular adhesion. The main intracellular molecules identified linking Dscs and Dsgs with the intermediate filament network are Plakoglobin (PG), Plakophilins (PPs) and Desmoplakin (DP). Previous studies on desmosome-mediated adhesion have focused on the intracellular domains of Dsc and Dsg because of their capacity to interact with PG, PPs and DP. This study examines the role of the extracellular domain of Dsg1 upon desmosome stability in MDCK cells. Dsg1 was constructed containing an extracellular deletion (Dsg delta 1EC) and was expressed in MDCK cells. A high expressor Dsg delta 1EC/MDCK clone was obtained and analysed for its capacity to form desmosomes in cell monolayers and when growing under mechanical stress in three-dimensional collagen cultures. Phenotypic changes associated with the ectopic expression of Dsg1 delta EC in MDCK cells were: disturbance of the cytokeratin network, a change in the quality and number of desmosomes and impairment of the formation of cysts in suspension cultures. Interestingly, Dsg1 delta EC was not localized in desmosomes, but was still able to maintain its intracytoplasmic interaction with PG, suggesting that the disruptive effects were largely due to PG and/or PP sequestration.

Genomic organization and amplification of the human desmosomal cadherin genes DSC1 and DSC3, encoding desmocollin types 1 and 3.

The desmosomal cadherins comprise the desmocollins and desmogleins and are involved in epithelial cell-cell adhesion. There are three desmocollins (DSC 1-3) and three desmogleins (DSG 1-3) that are expressed in a tissue- and development-specific manner. Desmosomal proteins have been implicated in a number of disorders characterized by loss of cell-cell adhesion and trauma-induced skin fragility. Therefore, the desmocollins are potential candidates for genodermatoses involving epithelial tissues. In order to screen the entire DSC1 and DSC3 genes, we have characterized their intron-exon organization. The DSC1 gene comprises 17 exons spanning approximately 33 kb on 18q12.1, and the DSC3 gene comprises 17 exons spanning approximately 49 kb on 18q12.1. We have also developed a comprehensive PCR-based mutation detection strategy for desmocollins 1, 2, and 3 using primers placed on flanking introns followed by direct sequencing of the PCR products.

N-terminal deletion in a desmosomal cadherin causes the autosomal dominant skin disease striate palmoplantar keratoderma.

The N-terminal extracellular domain of the cadherins, calcium-dependent cell adhesion molecules, has been shown by X-ray crystallography to be involved in two types of interaction: lateral strand dimers and adhesive dimers. Here we describe the first human mutation in a cadherin present in desmosome cell junctions that removes a portion of this highly conserved first extracellular domain. The mutation, in the DSG1 gene coding for a desmoglein (Dsg1), results in the deletion of the first and much of the second beta-strand of the first cadherin repeat and part of the first Ca2+-binding site, and would be expected to compromise strand dimer formation. It causes a dominantly inherited skin disease, striate palmoplantar keratoderma (SPPK), mapping to chromosome 18q12.1, in which affected individuals have marked hyperkeratotic bands on the palms and soles. In a three generation Dutch family with SPPK, we have found a G-->A transition in the 3" splice acceptor site of intron 2 of the DSG1 gene which segregated with the disease phenotype. This causes aberrant splicing of exon 2 to exon 4, which are in-frame, with the consequent removal of exon 3 encoding part of the prosequence, the mature protein cleavage site and part of the first extracellular domain. This mutation emphasizes the importance of this part of the molecule for cadherin function, and of the Dsg1 protein and hence desmosomes in epidermal function.

Clustered cadherin genes: a sequence-ready contig for the desmosomal cadherin locus on human chromosome 18.

We describe the assembly of a cosmid and PAC contig of approximately 700 kb on human chromosome 18q12 spanning the DSC and DSG genes coding for the desmocollins and desmogleins. These are members of the cadherin superfamily of calcium-dependent cell adhesion proteins present in the desmosome type of cell junction found especially in epithelial cells. They provide the strong cell-cell adhesion generated by this type of cell junction for which expression of both a desmocollin and a desmoglein is required. In the autoimmune skin diseases pemphigus foliaceous and pemphigus vulgaris (PV), where the autoantigens are, respectively, encoded by the DSG1 and DSG3 genes, severe areas of acantholysis (cell separation), potentially life-threatening in the case of PV, are evident. Dominant mutations in the DSG1 gene causing striate palmoplantar keratoderma result in hyperkeratosis of the skin on the parts of the body where pressure and abrasion are greatest, viz., on the palms and soles. These genes are also candidate tumor suppressor genes in squamous cell carcinomas and other epithelial cancers. We have screened two chromosome 18-specific cosmid libraries by hybridization with previously isolated YAC clones and DSC and DSG cDNAs, and a whole genome PAC library, both by hybridization with the YACs and by screening by PCR using cDNA sequences and YAC end sequence. The contigs were extended by further PCR screens using STSs generated by vectorette walking from the ends of the cosmids and PACs, together with sequence from PAC ends. Despite screening of two libraries, the cosmid contig still had four gaps. The PAC contig filled these gaps and in fact covered the whole locus. The positions of 45 STSs covering the whole of this region are presented. The desmocollin and desmoglein genes, which are about 30-35 kb in size, are quite well separated at approximately 20-30 kb apart and are arranged in two clusters, one DSC cluster and one DSG cluster, which are transcribed outward from the interlocus region. The order of the genes is correlated with the spatial order of gene expression in the developing mouse embryo, and this, and previous transgenic experiments, suggests that long-range genetic elements that coordinate expression of these genes may be present. The complete bacterial clone contig described in this paper is thus a resource not only for future sequencing but also for investigations into the control of expression of these clustered genes.

Antisense expression of a desmocollin gene in MDCK cells alters desmosome plaque assembly but does not affect desmoglein expression.

The desmocollins are one of two types of putative adhesive proteins present in the desmosome type of cell junctions, the other type being the desmogleins; both are members of the cadherin superfamily. Each type of desmosomal cadherin occurs as a number of isoforms which have differing tissue distribution; within stratifying epithelia some isoforms occur only suprabasally. We have sought to analyse desmocollin function by reducing the amount of protein using antisense gene expression in the widely studied Madin-Darby canine kidney (MDCK) cell line. Although this is a simple epithelial cell line, we show by Northern blot analysis that it expresses multiple isoforms of the desmosomal cadherins. Desmocollins DSC2 and DSC3 and desmogleins DSG2 and DSG3 (the pemphigus vulgaris antigen PVA) were detected, but DSC1 and DSG1, which are present exclusively in the suprabasal layers of the epidermis, were absent. The major desmocollin isoform was the type 2 (DSC2). A DSC2 clone isolated from a MDCK cDNA library had the same cell adhesion recognition sequence (Phe-Ala-Thr) as human, bovine and mouse type 2 isoforms. This sequence appears diagnostic for the three desmocollin isoforms. This cDNA clone was used to isolate a genomic DSC2 clone; antisense expression of this clone in MDCK cells resulted in a drastic reduction of desmocollin protein as judged by Western blots; Dsc3 was not upregulated to compensate for the loss of Dsc2. This antisense expression significantly altered desmosome assembly. There was a loss of punctate staining evident when using a desmosome plaque protein (desmoplakin) antibody. Electron microscopy revealed that there was a reduction in the number of desmosomes and a notable increase in the asymmetry of plaques between adjacent cells. Immunolabelling showed that similar levels of desmogleins and E-cadherin were present. Immunoelectron microscopy also showed that many vesicular structures were labelled, at intervals along the lateral membranes between cells. The distinctive loose organization of the remaining desmosomes may originate in modifications to the targeting and incorporation of proteins into fully assembled plaques. Other junctions were unaffected and the cells maintained their integrity as a confluent monolayer.

Coexpression of both types of desmosomal cadherin and plakoglobin confers strong intercellular adhesion.

Desmosomes are unique intercellular junctions in that they invariably contain two types of transmembrane cadherin molecule, desmocollins and desmogleins. In addition they possess a distinct cytoplasmic plaque structure containing a few major proteins including desmoplakins and the armadillo family member plakoglobin. Desmosomal cadherins are putative cell-cell adhesion molecules and we have tested their adhesive capacity using a transfection approach in mouse L cells. We find that L cells expressing either one or both of the desmosomal cadherins desmocollin 2a or desmoglein 1 display weak cell-cell adhesion activity that is Ca2+-dependent. Both homophilic and heterophilic adhesion could be detected. However, co-expression of plakoglobin with both desmosomal cadherins, but not with desmoglein 1 alone, resulted in a dramatic potentiation of cell-cell aggregation and the accumulation of detergent-insoluble desmosomal proteins at points of cell-cell contact. The effect of plakoglobin seems to be due directly to its interaction with the desmosomal cadherins rather than to its signalling function. The data suggest that the desmosome may obligatorily contain two cadherins and is consistent with a model in which desmocollins and desmogleins may form side by side heterodimers in contrast to the classical cadherins that are homodimeric. Plakoglobin may function by potentiating dimer formation, accretion of dimers to cell-cell contact sites or desmosomal cadherin stability.

Characterization of the regulatory regions in the human desmoglein genes encoding the pemphigus foliaceous and pemphigus vulgaris antigens.

The adhesive proteins in the desmosome type of cell junction consist of two members of the cadherin superfamily, the desmogleins and desmocollins. Both desmogleins and desmocollins occur as at least three different isoforms with various patterns of expression. The molecular mechanisms controlling the differential expression of the desmosomal cadherin isoforms are not yet known. We have begun an investigation of desmoglein gene expression by cloning and analysing the promoters of the human genes coding for the type 1 and type 3 desmogleins (DSG1 and DSG3). The type 1 isoform is restricted to the suprabasal layers of the epidermis and is the autoantigen in the autoimmune blistering skin disease pemphigus foliaceous. The type 3 desmoglein isoform is also expressed in the epidermis, but in lower layers than the type 1 isoform, and is the autoantigen in pemphigus vulgaris. Phage lambda genomic clones were obtained containing 4.2 kb upstream of the translation start site of DSG1 and 517 bp upstream of the DSG3 start site. Sequencing of 660 bp upstream of DSG1 and 517 bp upstream of DSG3 revealed that there was no obvious TATA box, but a possible CAAT box was present at -238 in DSG1 and at -193 in DSG3 relative to the translation start site. Primer extension analysis and RNase protection experiments revealed four putative transcription initiation sites for DSG1 at positions -163, -151, -148 and -141, and seven closely linked sites for DSG3, the longest being at -140 relative to the translation start site. The sequences at these possible sites at -166 to -159 in DSG1 (TTCAGTCC) and at -124 to -117 in DSG3 (CTTAGACT) have some similarity to the initiator sequence (CTCANTCT) described for a TATA-less promoter often from -3 to +5, and the true transcription initiator site might therefore be the A residue in these sequences. There were two regions of similarity between the DSG1 and DSG3 promoters just upstream of the transcription initiation sites, of 20 and 13 bp, separated by 41 bp in DSG1 and 36 bp in DSG3. The significance of these regions of similarity remains to be elucidated, but the results suggest that they represent a point at which these two desmoglein genes are co-ordinately regulated. Analysis of the upstream sequences revealed GC-rich regions and consensus binding sites for transcription factors including AP-1 and AP-2. Exon boundaries were conserved compared with the classical cadherin E-cadherin, but the equivalent of the second cadherin intron was lacking. A 4.2 kb region of the human DSG1 promoter sequence was linked to the lacZ gene reporter gene in such a way that there was only one translation start site, and this construct was used to generate transgenic mice. We present the first transgenic analysis of a promoter region taken from a desmosomal cadherin gene. Our results suggest that the 4.2 kb upstream region of DSG1 does not contain all the regulatory elements necessary for correct expression of this gene but might have elements that regulate activity during hair growth.

Hierarchical expression of desmosomal cadherins during stratified epithelial morphogenesis in the mouse.

Desmosomes contain two heterogeneous families of specialized cadherins (desmogleins or Dsgs and desmocollins or Dscs), subtypes of which are known to be expressed in tissue-specific and differentiation-dependent patterns in adult epithelial tissues. To examine the temporal and spatial order in which the individual desmosomal cadherins are expressed during stratified epithelial development we have obtained partial cDNA clones of all six murine desmosomal cadherins and have carried out in situ hybridization analysis on E12.5 to E16.5 mouse embryos. The results indicate that the type 2, type 3 and type 1 desmosomal cadherin messages are not obligatorily expressed as pairs during stratified epithelial morphogenesis. Instead the individual genes appear to be transcribed in hierarchical, overlapping temporal and spatial patterns extending from DSG2 to DSC1. DSG2 was the most uniformly expressed message in all E12.5 epithelia, gradually becoming confined to the basal cell layers during epithelial stratification indicating that its transcription was restricted to undifferentiated cells. In contrast, DSC2 message was expressed variably in early epithelia and was strongly upregulated in the suprabasal cell layers during the stratification of wet-surfaced epithelia. DSC3 message was expressed before that of DSG3 in the dental and lingual epithelium where its spatial distribution matched that of DSG2, but after DSG3 in the non-glandular gastric epithelium. DSC3 transcripts became confined to the lower layers of stratifying epithelia but were usually less basally restricted than those of DSG2. Like DSC2, DSG3 mRNA was strongly upregulated in the suprabasal layers of wet-surfaced epithelia as they stratified. Upregulation of DSG1 message was temporally linked to that of DSG3 in all tissues apart from the non-glandular gastric epithelium.

Exon-intron organization of the human type 2 desmocollin gene (DSC2): desmocollin gene structure is closer to "classical" cadherins than to desmogleins.

The cadherins are a superfamily of calcium-dependent glycoproteins that are cell adhesion molecules. Two families of cadherins, the desmocollins (Dsc) and desmogleins (Dsg), are found only in the desmosome type of cell-cell junction. They are each present in at least three different isoforms with differing spatial and temporal distributions and are specified by two clusters of closely linked genes on human chromosome 18q12.1. The human DSC2 gene, coding for the most widely distributed form of the desmocollins, has been found to consist of more than 32 kb of DNA. By using PCR we have determined the exon-intron organization. The gene is arranged into 17 exons ranging in size from 46 to 258 bp; exon 16 is alternatively spliced, giving rise to the a and b forms of the protein. This has revealed a remarkable degree of conservation of intron position with other cadherins. The desmocollin exon-intron organization is more similar to the so-called classical cadherins than to the desmogleins, especially in the cytoplasmic domain. Intron 1 is the largest in DSC2, as it is in the desmogleins, in contrast to the classical cadherins, where intron 2 is extremely large; this latter intron is missing from the desmogleins.

A YAC contig joining the desmocollin and desmoglein loci on human chromosome 18 and ordering of the desmocollin genes.

The desmocollins and desmogleins are members of the cadherin family of adhesive proteins present in the desmosome type of cell-cell junction. All of the known desmoglein and desmocollin isoforms, which have differing tissue and developmental distributions, are coded by very closely linked genes at 18q12.1. We have previously described YAC clones carrying all three known desmoglein (DSG) genes. We have now isolated YAC clones that carry all three known desmocollin genes (DSC1, 2, and 3) from two libraries and also isolated clones that join the DSC locus to the DSG locus, forming a complete contig for the region. Absence of chimeric ends for some of the YACs was confirmed by isolating Vectorette PCR products for the YAC ends and mapping the derived DNA sequences back to other YACs from CEPH. The whole DSC/DSG gene complex occupies no more than about 700 kb, and the genes are arranged in the order cen-3'-DSC3-DSC2-DSC1-5'-5'-DSG1-DSG3-D SG2-3'-tel, so that the two gene clusters are transcribed outward from the interlocus region. A P1 clone carrying part of DSC2 and DSC3 confirmed the relative orientation of transcription of these two genes. The conservation of close genetic linkage may be of trivial importance related to the recent duplication of these genes or may be because there is a region within the locus that is involved in coordinating the expression of the desmoglein and desmocollin genes.

Cloning and transcriptional analysis of the promoter of the human type 2 desmocollin gene (DSC2).

The desmocollins, together with the desmogleins, are members of the cadherin family and constitute the adhesive proteins of the desmosome type of cell-cell junction. Here we describe a study of the promoter of the human form of the DSC2 gene which is the equivalent of the first isoform expressed in the developing mouse embryo and that has the most widespread tissue distribution in epithelia and also in desmosome-bearing non-epithelial tissues. Analysis of the 5' upstream region by DNA sequencing and Southern blotting suggested that it contained a CpG island, and a major site of transcription initiation 201 bp upstream of the translation start site was found by RNase protection and primer extension. There were no obvious CCAAT or TATA boxes present. Analysis of 1.9 kb upstream of the translation start site revealed consensus binding sites for transcription factors including Ap-2 and Sp-1, and motifs common to the promoters of other epithelially expressed genes such as keratin 14 and the desmoglein genes DSG1 and DSG3. Deletion derivatives defined a promoter of 525 bp which was active in epithelial cells and in mouse blastocysts with an intact epithelium. This promoter showed reduced expression in non-epithelial cells.

Expression of the "skin-type" desmosomal cadherin DSC1 is closely linked to the keratinization of epithelial tissues during mouse development.

Desmosomal junctions contain two classes of desmosomal cadherin, the desmocollins and the desmogleins, each of which occurs as three distinct isoforms. To investigate the role of the "skin-type" desmosomal cadherins (desmocollin 1 and desmoglein 1) in the formation of keratinized epithelial structures, we have now cloned full-length mouse desmocollin 1 complementary deoxyribonucleic acid and examined the expression of desmocollin 1 and desmoglein 1 and messages during murine embryonic development by in situ hybridization. In the general body epidermis, desmocollin 1 and desmoglein 1 transcripts both showed considerable upregulation at 15.5 d, which is after the onset of stratification and before the start of keratinization. Before this the epidermis expressed low levels of desmocollin 1 message, although the desmoglein 1 signal was always stronger and more extensive. In the tongue, expression of desmocollin 1 message occurred several days after desmoglein 1 and coincided with the formation of the keratinizing filiform papillae. Desmoglein 1 message was also detected in epithelial tissues in which desmocollin 1 was absent, suggesting that expression of the two "skin-type" desmosomal cadherins was not tightly coupled during embryonic development. Human desmocollin 1 monoclonal antibodies that cross-reacted with mouse skin and tongue indicated that desmocollin 1 protein was first expressed in those outermost epithelial cells destined to form the keratinized layers of the stratum corneum or the papillae. The results suggest that expression of desmocollin 1 is closely associated with the keratinization of epithelial tissues during mouse development.

The desmocollins of human foreskin epidermis: identification and chromosomal assignment of a third gene and expression patterns of the three isoforms.

A third human desmocollin, designated DSC3, was identified in foreskin epidermis by reverse transcriptase-polymerase chain reaction (PCR) using degenerate desmocollin primers. cDNA clones covering the entire coding sequence of the longer DSC3 splice variant were isolated and sequenced. Sequence comparisons indicated that this new desmocollin showed greater homology (67% amino acid identity) with the original human desmocollin (now designated DSC2) than with DSC1 (52% amino acid identity) although it had a unique potential cell adhesion recognition site (YAS). DSC3 was assigned to chromosome 18 by PCR analysis of rodent-human somatic cell hybrids, where it appears to be closely linked to all the other desmosomal cadherin genes. The expression of the three human desmocollins was examined in foreskin epidermis by in situ hybridization with 3'-untranslated riboprobes and by immunofluorescence with isoform-specific anti-peptide antibodies. DSC1 was present in the upper spinous/granular layers but not in the basal/lower spinous layers of the tissue. DSC2 and DSC3 were present in most of the living layers of the epidermis. DSC1 was not detected in any of the nonkeratinizing human epithelia examined (buccal mucosa, cervix, esophagus), indicating that it is specific for the keratinizing epithelium of the epidermis. However, all these internal epithelia expressed DSC2 and DSC3, and both were present in most of the living layers of the tissues including the basal layers.

Regulation of desmocollin transcription in mouse preimplantation embryos.

The 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.