We are developing the fat-tailed dunnart as a novel laboratory model in which we can develop advanced genetic engineering and assisted reproductive technologies for marsupials. My project defined the process of early gonad formation in this species. Typically, the process of gonadal sex determination begins around the time of birth or shortly thereafter in marsupials. As in all mammals, the testis begins to differentiate before the ovary, with SOX9 expression in developing Sertoli cells being one of the first indications that the gonad has passed the indifferent stage. We examined gonadal development in the fat-tailed dunnart using histology and immunofluorescence staining. We found that testis differentiation begins at 2 days post-partum (d.p.p.) with expression of SOX9 in the testis primordia. Clear ovarian differentiation was evident by day 8 d.p.p. These processes seem to occur around the same time relative to birth as seen in less altricial marsupials.
In mammals, primordial germ cells arise outside of the embryo and must undergo migration in order to reach the developing gonad. Once in the gonad, the surrounding somatic environment dictates their differentiation into sperm or eggs. We saw arrival of putative primordial germ cells (PGCs) in the gonads of both sexes at 2 d.p.p. The primary route for PGC migration in eutherian mammals is often through the hindgut and dorsal mesentery. In marsupials, the migratory path of PGCs is variable. For example, in the bandicoot PGCs migrate through the hindgut and dorsal mesentery, however in the tammar and brushtail possum, PGCs are excluded from the hindgut entirely. We are aiming to characterise the PGC migration pathway in the fat-tailed dunnart to help better understand early developmental process in the dunnart. Improving our knowledge of this species’ biology will support its establishment as a practical and robust and laboratory model for marsupial research.