Sexual development in marsupials: Genetic characterization of bandicoot siblings with scrotal and testicular maldevelopment

In marsupials testis determination requires the presence of a Y chromosome. The sex determining region on the Y gene (SRY) is necessary for testicular development in eutherians and it is assumed to play a similar role in mars upials. Relatively few studies have investigated the genetic basis of sexua l development, and as yet there is no direct evidence that SRY is required for testis development in marsupials. Studies on intersexual marsupials hav e revealed a fundamental difference between marsupial and eutherian sex det ermination. The scrotum of marsupials is analogous, not homologous, to the eutherian scrotum and is under the control of X-linked genes not androgens. The current study describes two bandicoot (Isoodon macrourus) siblings. Bo th siblings had underdeveloped male reproductive tracts and testicular dysg enesis, one was ascrotal and the other had a diminutive scrotum. Their kary otypes were normal for this species which eliminates the Y chromosome from some somatic tissues. SRY was detected by Southern blotting. SRY, ubiquitin activating enzyme-1 on the Y (UBE1Y) and glucose 6-phosphate dehydrogenase (G6PD) gene expression were examined. UBE1Y was widely expressed in many t issues. SRY gene expression was much lower than normal in the abnormal sibl ings and may be responsible for their failure of testicular and epididymal development. The cause of their scrotal abnormalities is unknown. It is pos sible that the separate defects of scrotal and testis development in the tw o siblings, which had normal relatives, were due to a mutation in a gene co mmon to both developmental pathways. Mol. Reprod. Dev. 57:127-134, 2000. (C ) 2000 Wiley-Liss, Inc.