Indranath GHOSAL

GenESiS, Gonadal development and Effect of temperature on Sex determination in the Small-spotted catshark

Sex determination is poorly explored in Chondrichthyes, the oldest extant clade of jawed vertebrates, so occupying a key position in evolution for a better understanding of their origin and diversifications. Sex determination in this group is mostly restricted to cytogenetic approaches looking at sex chromosome differentiation on karyotypes of different species. At a molecular level, sex-linked single nucleotide polymorphisms were identified in a ray. In addition to genetic sex determination, various environmental parameters like temperature, nutrients, pH, oxygen concentration or social factors can also affect the sex. Environmental sex determinism has never been investigated in Chondrichthyes, which does not allow us to anticipate which consequences the global climate change will have on these animals. Considering this, the GenESiS project aims to understand the gonad ontogeny, sex determination and differentiation in the small-spotted catshark. It is based on the hypotheses that the gonad ontogeny and sex differentiation pattern may be similar to other vertebrates and that sex determination mays be affected by the environment, mainly by the temperature, along with genetic sex determination. To achieve the objectives, gonad ontogeny will be characterized based on both histological and molecular techniques for the detection of apoptotic cells and proliferating cells. Next, molecular factors involved in the process of sex determination and/or differentiation will be studied. Classical candidates will be considered but also a new sequence identified in a preliminary study. The expression of these candidate genes will be analyzed at spatial and temporal levels using immunohistochemistry, in situ hybridization RT-qPCR. Finally, embryos will be exposed to higher temperature to detect a potential environmental sex determination and to contribute to the modelling of ecological niche model. This project approaches the question of sex determination and differentiation in a chondrichthyan species in an innovative and original way, which should shake up the current knowledge in this field.