Sea Urchin Neural Development

Sea urchins have a larval nervous system that arises during gastrulation within the ectoderm at the animal pole of the embryo. Subsequently a set of neurons that are associated with developing ciliary band appear. We have used antibodies to neurotransmitters and other neuronal markers to identify the complexity of this larval nervous systems and describe its development (Nakajima et al. 2004; Burke et al. 2006).

A, B. The larval nervous systems in sea urchins emanates from the ciliar band. Neurons within ciliary bands project axons throughout the larval body. Between the preoral arms anterior to the mouth, there is an apical ganglion containing serotonergic cells (red in C). There are also ganglia associated with the larval mouth that project axons into the esophagus.

The adult sea urchin develops as a rudiment on one side of the larval body. The adult nervous system develops within this rudiment independently of the larval nervous system. The adult radial nerves form with the primary podia in the rudiment and are joined at their proximal ends by a series of commisures that form the circumoral nerve ring.

The adult nervous system forms within the adult rudiment. The dense axons and cell bodies of the radial nerves are joined by a series of commisures.

We been involved in determining signalling events are necessary for the specification and patterning of neurons in early development (Yaguchi et al. 2006a, b). We have determined that the ligand Nodal secreted from the oral ectoderm patterns the neurogenic ectoderm by suppressing the formation of serotonergic neurons. Analysis of the sea urchin genome has revealed a large number of genes that mediate neural specification and patterning and promise to provide a means of testing specific hypotheses about urchin neural development.