Pascal SOURDAINE

Key words: Elasmobranchs - Spermatogenesis - Steroidogenesis - Spermatogonial stem cells – Cellular biology

Identification of early markers of spermatogenesis in the small spotted catshark (Scyliorhinus canicula L.).

Spermatogenesis start with the multiplication and differentiation of diploid spermatogonia and ends with the production of highly specialized haploid cells, spermatozoa. Continuous production of male gametes is dependent on the ability of spermatogonial stem cells (SSC) to renew while maintaining their stemness. This takes place within a specific microenvironment called the "niche" and involving autocrine and paracrine factors, these last ones secreted from the surrounding somatic cells. Our studies focus on the identification and functional characterization of the SSC and of the molecular players that control their self-renewal and differentiation using a Chondrichthyans model, the small spotted catshark (Scyliorhinus canicula). The identification of molecular markers is performed through proteomic and transcriptomic approaches on purified cells or testicular areas. Our studies also address the evolution of the niche of germline stem cells in Gnathostomes.

Evolution of GnRH systems and of their regulatory neuropeptides in endocrine and paracrine controls of spermatogenesis in the dogfish Scyliorhinus canicula.
 
The hypothalamic-pituitary system is the main regulator of reproduction and its evolution was accompanied by a specialization of its regulatory peptides that have tissue distributions and broader functions in invertebrates. These peripheral functions have persisted in vertebrates and their studies are emerging in the context of understanding effects of environmental cues on reproduction. In an evolutionary context, it is relevant to include Chondrichthyes as the sister group of Osteichthyes (bony vertebrates) to better understand the evolution of GnRH systems and of their regulatory neuropeptides (KNDy: Kisspeptin, Neurokinin, Dynorphin; RFRP3, the mammalian orthologue of GnIH). Analyses of genomes from Chondrichthyes have allowed identifying several actors implied in the control of growth, reproduction and energy homeostasis. GnRH and GnRHR genes as well as those of the KNDy network are also expressed in the male reproductive tract, asking about their paracrine function. Our goal is the study of the evolution of those neuropeptides and their involvement in endocrine and paracrine controls of spermatogenesis in the dogfish. The choice of S. canicula is motivated by its phylogenetic position, the organization of its central nervous system and its circulatory system (absence of portal system) and by the relative independence of its spermatogenesis from a gonadotropin regulation.