Chromosomal localisation of sex-specific BACs and of selected cDNAs identified by microdissection in two tilapia species, Oreochromis niloticus and 'Oreochromis aureus

Cichlid fish of the Tilapia group are an ideal model for studying sex determination. Sequencing of the Tilapia (Oreochromis niloticus) genome has started in USA and France and genetic and physical linkage maps based on high resolution fingerprints of BAC clones are produced. We have in charge the chromosomal anchoring of some sex linked BACs from the genetic mapping. Some BAC libraries constructed from a male O. niloticus have been assembled into a physical map. Generally, species with a major sex determination locus on linkage group 1 (LG1) are male heterogametic and species with a major sex determination locus on linkage group 3 (LG3) are female heterogametic. In order to confirm that LG1 and LG3 are on two different, unlinked chromosomes, we physically mapped the sex-linked markers by chromosomal FISH on the chromosomes of two closely related Tilapia species, O. niloticus and O. aureus. These experiments demonstrated that LG3 corresponds to the largest chromosome in the Tilapia karyotype, and that LG1 corresponds to a different, smaller chromosome. The chromosome pair corresponding to LG3 in O. niloticus has been manually microdissected and a series of cDNAs isolated from this microdissected product have been cloned, sequenced and selected for chromosomal FISH. Their hybridization helps to validate the results. (Texte intégral)