Meeting Abstract

S8.8  Tuesday, Jan. 6  Evolution of Sex Determination in East African Cichlid Fishes KOCHER, Thomas D; University of Maryland tdk@umd.edu

Sex determination is a fundamental developmental decision in which the bipotential gonad is directed into specific pathways of male or female development. Our long term goal is to discover and characterize the gene regulatory network responsible for this central developmental switch in vertebrates. We focus our experimental work on cichlid fishes, including cultured tilapias and the haplochromine cichlids of East Africa. These species descend from a common ancestor within the last 15MY and share most of the regulatory network for sex determination. Among these closely related species we have discovered at least four distinct sex determining loci. The Nile tilapia (Oreochromis niloticus) has an XX-XY (male heterogametic) system controlled by a major gene near marker UNH995 on LG1. The blue tilapia (O. aureus ) has a WZ system near UNH168 on LG3 which is epistatic to the XY system on LG1. Malawi haplochromines segregate for an XY locus near UNH973 on LG7. At least four Malawi species also segregate for a WZ locus near cski on LG5. When both loci segregate in a single family, the W allele on LG5 trumps the XY locus on LG7. These four loci can be considered new mutants in the sex-determining pathway, which provide windows on the gene network underlying vertebrate sex determination. By comparing the function of regulatory networks in these species, we will gain insight into the structure of the network, and the mechanisms by which the output of the network is controlled by different genes.