Genomic characterization of human DSPG3

DSPG3, the human homolog to chick PG-Lb, is a member of the small leucine-r ich repeat proteoglycan (SLRP) family, including decorin, biglycan, fibromo dulin, and lumican. In contrast to the tissue distribution of the other SLR Ps, DSPG3 is predominantly expressed in cartilage. In this study, we have d etermined that the human DSPG3 gene is composed of seven exons: Exon 2 of D SPG3 includes the start codon, exons 4-7 code for the leucine-rich repeats, exons 3 and 7 contain the potential glycosaminoglycan attachment sites, an d exon 7 contains the potential N-glycosylation sites and the stop codon. W e have identified two polymorphic variations, an insertion/deletion compose d of 19 nucleotides in intron 1 and a tetranucleotide (TATT)(n) repeat in i ntron 5. Analysis of 1.6 kb of upstream promoter sequence of DSPG3 reveals three TATA boxes, one of which is 20 nucleotides before the transcription s tart site. The transcription start site precedes the translation start site by 98 nucleotides. There are 14 potential binding sites for SOX9, a transc ription factor present in cartilage, in the promoter, and in the First intr on of DSPG3. We have examined the evolution of the SLRP gene family and Fou nd that gene products clustered together in the evolutionary tree are encod ed by genes with similarities in genomic structure. Hence, it appears that the majority of the introns in the SLRP genes were inserted after the diffe rentiation of the SLRP genes from an ancestral gene that was most likely co mposed of 2-3 exons.