Evolution of sex hormone-binding globulin gene expression in the primate testis

In lower mammals testicular sex hormone-binding globulin (SHBG), also known as androgen binding protein, is well known to be a product of the Sertoli cells. However in humans, testicular SHBG is a product of the germ cells, is expressed from an upstream promoter and contains an alternative first exon 1A. Examination of testicular SHBG transcripts from members across primate suborders revealed that transcripts containing exon 1A are unique to Hominoids and Old World Monkeys. In contrast testicular SHBG transcripts in gray mouse lemur contained the proximal exon 1, while no evidence for SHBG expression could be detected in marmoset monkey testes. In general, the exonic identity of primate testicular SHBG transcripts could be predicted based on the structure of their genes 5 regulatory region and we show that they change through the primate clade. This work provides insights into how molecular evolution of higher primate SHBG genes has resulted in distinct changes in how it is expressed in their testes.