Inducing sex reversal of the urogenital system of marsupials

Marsupials differ from eutherian mammals in their reproductive strategy of delivering a highly altricial young after a short gestation. The young, with its undeveloped organ systems completes its development post-natally, usually within a pouch. The young is dependent on milk with a composition that varies through lactation to support its growth and changing needs as it matures over a lengthy period. Gonadal differentiation occurs after birth, providing a unique opportunity to examine the effects of hormonal manipulations on its sexual differentiation of the highly accessible young. In marsupials a difference in the migration of the urinary ducts around the genital ducts from eutherian mammals results in the unique tammar reproductive tract which has three vaginae and two cervices, and two distinctly separate uteri. In the tammar wallaby, a small member of the kangaroo family, we showed that virilisation of the Wolffian duct, prostate and phallus depends on an alternate androgen pathway, which has now been shown to be important for virilisation in humans. Through hormonal manipulations over differing time periods we have achieved sex reversal of both ovaries and testes, germ cells, genital ducts, prostate and phallus. Whilst we understand many of the mechanisms behind sexual differentiation there are still many lessons to be learned from understanding how sex reversal is achieved by using a model such as the tammar wallaby. This will help guide investigations into the major questions of how and why sex determination is achieved in other species. This review discusses the control and development of the marsupial urogenital system, largely drawn from our studies in the tammar wallaby and our ability to manipulate this system to induce sex reversal.