The aristaless homeobox gene, ARX, belongs to a large family of homeodomain transcription factors with essential roles in forebrain, pancreas, muscle tissues and testes development in human and mouse. Mutation of ARX in humans results in mental retardation with or without ambiguous genitalia. We used comparative analyses to examine the evolutionary conservation of the mammalian ARX gene. We characterised ARX in a marsupial, the tammar wallaby, to determine if this gene is highly conserved in the homeodomain, aristaless domain, octapeptide motif and polyalanine tracts of all mammals. We further investigated the mRNA distribution in the developing head of tammar with in situ hybridisation, and found that it is expressed in forebrain and olfactory bulb as expected. Besides these regions, very strong expression was detected in the epithelium of the tongue and nasal pits. In the gonads, there is very strong staining in the interstitial cells and some of the germ cells in the developing ovary; strong staining was also seen in the cytoplasm of Sertoli cells and some of the germ cells, weak staining was also detected in the interstitium of the testis, possibly within the vessel endothelial cells and interstitial fibroblast-like cells. In addition, we investigated mRNA distribution in adult testes based on a very strong signal observed with northern blotting. Interestingly, mRNA expression was restricted to the round spermatids, and was not seen before or after this stage. In order to confirm this new role for ARX in the adult testis, we further investigated mRNA distribution of Arx in adult mouse testis, and found the same expression pattern, which implies a conserved function for ARX in spermatogenesis and may explain why humans with ARX mutations are infertile. This is the first report that ARX gene is involved in spermatogenesis in addition to its conserved roles in early mammalian development.
Gpbox (Psx2), a Homeobox Gene Preferentially Expressed in Female Germ Cells at the Onset of Sexual Dimorphism in Mice
