In comparison to the conserved XX-XY system in mammals, sex determining mechanisms in gonochoristic fishes are considered complex and heterogeneous. For instance, there are many other types of chromosomal system of sex determination besides the mammalian XX/XY and avian ZZ/ZW. According to the environmental conditions, such systems can be modulated by several physical parameters and among them the water temperature seems to be a potent modulator in fishes. Studies on temperature effects on sex (TSD) have advanced in many fish groups, however, studies on the genotypic sex determination are still not well known even in species with whole genome sequenced. The only report of a sex-determining gene in fish is restricted to the medaka species (Oryzias genus).During the PhD project, the candidate has developed an extensive research on the molecular mechanisms behind GSD (genotypic sex determination) in one economically important teleost from inland waters of southern region of South America: the Patagonian pejerrey (Odontesthes hatcheri, Atherinopsidae). A stable strain inheriting a sex-specific SNP marker was established (Ehi-M13) and a strong candidate for testis determining gene belonging to the TGF-beta family present only in the genome of males was identified. Structural and expression analyses showed that this gene comprises a duplicated copy of amh (anti-Müllerian hormone) which displayed similar expression patterns to that of medaka sex determining gene dmy/dmrt1bY. Physical mapping on metaphase chromosomes allowed for the first time the identification of the Y chromosome in an Atheriniformes species. Within this context, in the present project the O. hatcheri sex-determining candidate gene will be investigated in other closely related species, particularly in those belonging to Odontesthes genus in order to unravel the evolution of mechanisms of sex determining (with focus on GSD) in the Atherinopsidae family.Samples will be collected in southern coast of Brazil, southeastern coast of Argentina and inland waters from Chile. Part of the processing for genetic analyses will be conducted in collaboration with the Laboratório de Ictiofisiologia y Acuicultura, Instituto de Investigaciones Biotecnológicas (Chascomús, Argentina) and with the Laboratory of Population Biology, Tokyo University of Marine Science and Technology (Tokyo, Japan). The techniques comprise basically in PCR with genomic DNA, RT-PCR, genome walking, subcloning, sequencing and FISH analyses. The findings of this study will have great implications toward the clarification of molecular mechanisms of sex determination not only in this group, characterized by species with sex determination affected by environmental factors (or ESD) but also in teleosts in general.
News published in Agência FAPESP Newsletter about the scholarship: