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 de smocollins and desmogleins, These are members of the cadherin superfamily o f calcium-dependent cell adhesion proteins present in the desmosome type of cell junction found especially in epithelial cells. They provide the stron g cell-cell adhesion generated by this type of cell junction for which expr ession of both a desmocollin and a desmoglein is required, In the autoimmun e 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 t he case of PV, are evident. Dominant mutations in the DSG1 gene causing str iate palmoplantar keratoderma result in hyperkeratosis of the skin on the p arts of the body where pressure and abrasion are greatest, viz,, on the pal ms and soles, These genes are also candidate tumor suppressor genes in squa mous cell carcinomas and other epithelial cancers, We have screened two chr omosome 18-specific cosmid libraries by hybridization with previously isola ted 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 usi ng STSs generated by vectorette walking from the ends of the cosmids and PA Cs, together with sequence from PAC ends, Despite screening of two librarie s, 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, w hich 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 DS G cluster, which are transcribed outward from the interlocus region, The or der 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 t hese 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, (C) 1999 Academic Press.