Abstract

The complex central (CNS) and peripheral nervous systems (PNS) of vertebrates have evolved from simpler nervous systems, arguably similar to those seen in living amphioxus. Amphioxus has far fewer neural cells than vertebrates, and probably also fewer types of cells. Such evolutionary change can be broken into three components: making lots more cells (control of proliferation/stem cell populations), organising those cells (patterning) and, probably, inventing new types of cells (differentiation). Focusing on placodes in the PNS and the spinal cord in the CNS , I will discuss our recent work aimed at understanding these changes, using the early-diverging chordate lineages amphioxus, ascidians and lampreys. For placodes we have used FACS -seq to profile types of sensory neurons, work aimed at developing vertebrate cell-type ‘fingerprints’ for comparative study. In the spinal cord we focus on the signalling pathways regulating cell proliferation and patterning, including the Notch, Wnt and Hh pathways and their roles in progenitor cell maintenance and patterned differentiation. Our overall aim is to define the gene regulatory changes behind morphological change in the early vertebrate nervous system.