29.4 Wednesday, Jan. 4 Role for a DM domain gene in male-specific reproductive development in the simultaneous hermaphrodite Schmidtea mediterranea. CHONG, T.*; NEWMARK, P.A.; Univ. of Illinois, Urbana-Champaign email@example.com
In simultaneous hermaphrodites, little is known about how sex-specific reproductive organs develop and whether male and female reproductive structures are co-dependent. The sexual strain of the freshwater planarian Schmidtea mediterranea is a good model in which to address this question: it is a cross-fertilizing, simultaneous hermaphrodite with male and female reproductive organs that develop post-embryonically. In this study, we examined a gene from the DM (doublesex/male-abnormal-3) domain gene family, Smed-dm4. DM domain genes are conserved transcription factors that regulate sexual differentiation across phyla. In situ hybridization to detect dm4 transcript in sexual planarians revealed expression in a subset of cells in the male gonads, male accessory reproductive organs, and the brain. Knockdown of dm4 results in disruption of the male components of the reproductive system, such as the sperm ducts, testes, and seminal vesicles. In these animals the testes, including the nanos-positive germline stem cells, are not detected. By contrast, the female reproductive organs appeared normal, as seen through the expression of nanos and other genes expressed in oocytes, oviducts, and glands around the copulatory apparatus. Our results suggest that dm4 plays a role in male-specific sexual development in planarians. The presence of sex-specific pathways in planarians like S. mediterranea could allow the evolution of simultaneous hermaphrodites into distinct male or female sexes, as seen in more derived flatworm species like the parasitic schistosomes. The role of dm4 in sexual development in lophotrochozoans provides additional evidence for the evolutionary conservation of sex determination mechanisms across metazoans.