Developmental study of the cerebellum in cartilaginous fishes: Towards the identification of primitive features of the cerebellar formation in gnathostomes

Abstract

This Thesis corresponds to a developmental study of the cerebellum in the shark Scyliorhinus canicula, which belongs to the gnathostome group with most primitive features of the cerebellum. The genoarchitecture of rostral hindbrain in this species appears very similar to that of other gnathostomes, and differences from that of agnatha showed possible genetic changes at the base of the evolutionary origin of the cerebellum. The combined analysis of cerebellar morphogenesis and genoarchitecture allowed: identifying consistent anatomical landmarks highly conserved, discerning the possible basal median-lateral cerebellar compartmentalization, and providing some evidence of the exclusive cerebellar origin from rhombomere 1. The developmental study and neurochemical characterization of the precerebellar nuclei showed shared traits between S. canicula and other jawed vertebrates. Besides, some evidence that migrating pathways of precerebellar nuclei precursors appeared very early in gnathostome evolution was observed. Therefore, present results may reveal the ancestral organization of the cerebellar system.