Cloning and expression of a DAX1 homologue in the chicken embryo

DAX1 is an unusual member of the orphan nuclear receptor family of transcri ption factors. Mutations in human DAX1 cause X-linked adrenal hypoplasia co ngenita, while abnormal duplication of the gene is responsible for male-to- female dosage-sensitive sex reversal. Based on these and other observations , DAX1 is thought to play a role in adrenal and gonadal development in mamm als. As DAX1 has not previously been described in any other vertebrate, a p utative avian DAX1 clone was isolated from an embryonic chicken (Gallus dom esticus) urogenital ridge cDNA library. The expression profile of this cDNA was then examined during gonadogenesis. The clone included the conserved 3 ' ligand-binding motif identified in humans and mice but the 5' region lack ed the repeat motif thought to specify a DNA-binding domain in mammals. Sou thern blot analysis and fluoresence in situ hybridisation mapping showed th at the gene is autosomal, located on chromosome 1q. Sequence comparisons sh owed that the putative chicken DAX1 protein has 63 and 60% identity with th e human and mouse proteins respectively over the region of the conserved li gand-binding domain. However, stronger identity (74%) exists with a putativ e alligator DAX1 sequence over the same region. Northern blotting detected a single 1.4 kb transcript in late embryonic chicken gonads, while RNase pr otection assays revealed expression in the embryonic gonads of both sexes d uring the period of sexual differentiation. Expression increased in both se xes during gonadogenesis, but was higher in females than in males. This is the first description of a DAX1 homologue in a non-mammalian vertebrate.