SEXYTROUT

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As opposed to the situation which can be observed in mammals and birds, who have retained a major system of sex determination for at least 100 million years, a wide diversity of mechanisms which determine sex exist in fish. More particularly, salmonides are thought to have a strictly genetic male heterogametie sex determination system (males XY and females XX). However, surprisingly, males have been observed in genetically female homozygotic lines(XX), obtained after gynogenesis of the Oncorhynchus mykiss rainbow trout. Genetic analysis of this masculinised phenotype (Mal) suggest that it could be due to a recessive mutation in a minor locus of  sex determination known as mal. This research project combines genetic, genomic and transcriptomic approaches, in order to identify this mal locus at the molecular level. Three converging strategies will be developed to achieve this objective. Firstly,  a positional cloning type approach should permit the localisation of the mal locus  on the rainbow trout's genetic map. Bacterial artificial chromosomes (BAC) covering this area will then be sequenced in order to identify genes which could correspond to mal. Secondly,a candidate gene type approach will aim to identify the genes involved in sex determination and sexual differentiation via bioinformatic analysis in rainbow trout sequence banks. These genes will then be mapped to test for their possible co-localisation with the mal locus. Thirdly, after characterisation of the gonad phenotype of mal individuals and the effect of temperature on their occurrence in genetically female the gene homozygous population, expression profiles will be studied for the different sexual phenotypes by DNA chip, quantitative PCR and in situ hybridisation so as to identify gene deregulations and genetic networks associated with this phenotype. These deregulated genes and their regulators, considered as mal candidates, will also be localised on the genetic map. The candidate genes identified by these three complimentary strategies, retained on the basis of their co-localisation with the mal locus and their expression profile compatible with a role in sex determination or sexual differentiation, will be sequenced with XX females and mal/mal males so as to determine the gene and the mutation responsible for the masculanised phenotype. Finally, the functional effects of the mal mutation on the gene product will be studied in vitro and in vivo. Three research teams with a recognised expertise in the field of sex determination and sexual differentiation in trout and other fish will interact within the framework of this project, with complimentary skills in genetics, genomics, transcriptomics, molecular physiology, evolutionary and developmental biology. This project will provide an unprecedented mass of information in genetics and molecular physiology in the sexual development of the rainbow trout, and will contribute greatly to a better understanding of the molecular and evolutionary basis of sex determination and sexual differentiation in fish. The results obtained will also permit the elucidation of a type of interaction between genome and environment modulating a phenotype. In an aquacultural context, it is also expected that a better knowledge of the genetic and environmental basis of this type of masculinisation will allow fish culturists to better monitor a comparable phenomenon which has appeared on farms in recent years. Finally, the decoding of environmental mechanisms which modulate gonadal differentiation would open the way  o the development of new sex monitoring methods in trout, based on temperature, as an alternative to the current steroidal treatments  used to produce XX male (neomales) founders of female monosex populations.

This project was labellised by the AQUIMER Pole of Competitiveness on 4 February 2008.

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