The X-linked aristaless gene, ARX, is essential for the development of the gonads, forebrain, olfactory bulb, pancreas, and skeletal muscle in mice and humans. Mutations cause neurological diseases, often accompanied by ambiguous genitalia. There are a disproportionately high number of testis and brain genes on the human and mouse X chromosomes. It is still unknown whether the X chromosome accrued these genes during its evolution or whether genes that find themselves on the X chromosome evolve such roles. ARX was originally autosomal in mammals and remains so in marsupials, whereas in eutherian mammals it translocated to the X chromosome. In this study, we examined autosomal ARX in tammars and compared it with the X-linked Arx in mice. We detected ARX mRNA in the neural cells of the forebrain, midbrain and hindbrain, and olfactory bulbs in developing tammars, consistent with the expression in mice. ARX was detected by RT-PCR and mRNA in situ hybridization in the developing tammar wallaby gonads of both sexes, suggestive of a role in sexual development as in mice. We also detected ARX/Arx mRNA in the adult testis in both tammars and mice, suggesting a potential novel role for ARX/Arx in spermiogenesis. ARX transcripts were predominantly observed in round spermatids. Arx mRNA localization distributions in the mouse adult testis suggest that it escaped meiotic sex chromosome inactivation during spermatogenesis. Our findings suggest that ARX in the therian mammal ancestor already played a role in male reproduction before it was recruited to the X chromosome in eutherians.
Hongshi Yu, Andrew J Pask, Yanqiu Hu, Geoff Shaw and Marilyn B Renfree
Yanqiu Hu, Hongshi Yu, Andrew J Pask, Deborah A O'Brien, Geoff Shaw and Marilyn B Renfree
A-kinase anchor protein 4 (AKAP4) is an X-linked member of the AKAP family of scaffold proteins that anchor cAMP-dependent protein kinases and play an essential role in fibrous sheath assembly during spermatogenesis and flagellar function in spermatozoa. Marsupial spermatozoa differ in structural organization from those of eutherian mammals but data on the molecular control of their structure and function are limited. We therefore cloned and characterized the AKAP4 gene in a marsupial, the tammar wallaby (Macropus eugenii). The gene structure, sequence, and predicted protein of AKAP4 were highly conserved with that of eutherian orthologues and it mapped to the marsupial X-chromosome. There was no AKAP4 expression detected in the developing young. In the adult, AKAP4 expression was limited to the testis with a major transcript of 2.9 kb. AKAP4 mRNA was expressed in the cytoplasm of round and elongated spermatids while its protein was found on the principal piece of the flagellum in the sperm tail. This is consistent with its expression in other mammals. Thus, AKAP4 appears to have a conserved role in spermatogenesis for at least the last 166 million years of mammalian evolution.
Yu Chen, Hongshi Yu, Andrew J Pask, Asao Fujiyama, Yutaka Suzuki, Sumio Sugano, Geoff Shaw and Marilyn B Renfree
The development of the mammalian phallus involves hormone-dependent mesenchymal–epithelial signalling mechanisms that contribute to urethral closure and regulation of phallus elongation and growth. In marsupials, most differentiation and growth of the phallus occurs post-natally, making them amenable to direct hormone treatment. Expression of IGFs, FGFs, EFNB2, MAFB, DLX5 and AP-1 mRNAs in the phallus at day 50 post-partum (pp) were altered after treatment of tammar wallaby young from day 20 to 40 pp with androgen, oestrogen or after castration at day 25 pp. However, the most interesting changes occurred in the IGF pathway genes. Androgen treatment upregulated IGF1 in female phalluses and oestrogen treatment upregulated IGF1 in male phalluses, but it was downregulated by castration. IGFBP3 was higher in female phalluses and downregulated by androgen. IGF1 expression was higher in all untreated male than in female phalluses from day 50 to 150 pp, but IGFBP3 had the reverse pattern. At day 90 pp, when urethral closure in males is progressing and male phallus growth is accelerating. IGF1 and PCNA protein were only detected in the male urorectal septum, suggesting for the first time that closure and elongation may involve IGF1 activation of cell proliferation specifically in male phalluses. These effects of sex steroids on gene expression and on the IGF1 signalling pathway in particular, suggest that the developing phallus may be especially susceptible to perturbation by exogenous hormones.