Development and regionalization of the telencephalon and peripheral associated systems in the shark Scyliorhinus canicula

Abstract

This thesis represents the first monographic study of the telencephalon and peripheral systems associated to it in an elasmobranch species, Scyliorhinus canicula, which is a crucial model from an evolutionary point of view. We present a thoughtful characterization of these structures from early embryonic development to adulthood, which intend to fill a gap in the knowledge about vertebrate telencephalon evolution and, particularly, about its development. We describe for the first time the development of the peripheral olfactory system and terminal nerve system in S. canicula and present evidences of their shared origin in the migratory mass. We also demonstrate that Pax6 cells located along the developing olfactory nerve are migrating neurons that might be acting as guidepost cells for axons travelling towards the olfactory bulb. Additionally, we delimit main pallial and subpallial subdivisions by means of the analysis of expression of key developmental genes as Dlx2, Nkx2.1, Tbr1, Lhx9, Emx1, Shh and Otp. This genetic approach also allowed us to analyze different tangential migratory routes originated in the subpallium. Finally, we study the connections of the proposed basal ganglia in juveniles of S. canicula which draw interesting conclusions about the identity of the striatum and the conservation of the dopaminergic nigrostriatal pathway in elasmobranchs.