Genomic organization of the human CD5 gene

CD5 is a member of the family of receptors which contain extracellular domains homologous to the type I macrophage scavenger receptor cysteine-rich (SRCR) domain. Here, we compare the exon/intron organization of the human CD5 gene with its mouse homologue, as well as with the human CD6 gene, the closest related member of the SRCR superfamily. The human CD5 gene spans about 24.5 kb and consists of at least 11 exons. These exons are conserved in size, number, and structure in the mouse CD5 homologue. No evidence for the biallelic polymorphism reported in the mouse could be found among a population of 100 individuals of different ethnic origins. The human CD5 gene maps to the Chromosome (Chr) 11q12.2 region, 82 kb downstream from the human CD6 gene, in a head-to-tail orientation, a situation which recalls that reported at mouse Chr 19. The exon/intron organization of the human CD5 and CD6 genes was very similar, differing in the size of intron 1 and the number of exons coding for their cytoplasmic regions. While several isoforms, resulting from alternative splicing of the cytoplasmic exons, have been reported for CD6, we only found evidence of a cytoplasmic tailless CD5 isoform. The conserved structure of the CD5 and CD6 loci, both in mouse and human genomes, supports the notion that the two genes may have evolved from duplication of a primordial gene. The existence of a gene complex for the SRCR superfamily on human Chr 11q (and mouse Chr 19) still remains to be disclosed.