Functional Role of Pax6 During Eye and Nervous System Development in the Annelid Capitella Teleta

The transcription factor Pax6 is an important regulator of early animal development. Loss of function mutations of pax6 in a range of animals result in a reduction or complete loss of the eye, a reduction of a subset of neurons, and defects in axon growth. There are no studies focusing on the role of pax6 during development of any lophotrochozoan representative, however, expression of pax6 in the developing eye and nervous system in a number of species suggest that pax6 plays a highly conserved role in eye and nervous system formation. We investigated the functional role of pax6 during development of the marine annelid Capitella teleta. Expression of pax6 transcripts in C. teleta larvae is similar to patterns found in other animals, with distinct subdomains in the brain and ventral nerve cord as well as in the larval and juvenile eye. To perturb pax6 function, two different splice-blocking morpholinos and a translation-blocking morpholino were used. Larvae resulting from microinjections with either splice-blocking morpholino show a reduction of the pax6 transcript. Development of both the larval eyes and the central nervous system architecture are highly disrupted following microinjection of each of the three morpholinos. The less severe phenotype observed when only the homeodomain is disrupted suggests that presence of the paired domain is sufficient for partial function of the Pax6 protein. Preliminary downstream target analysis confirms disruption in expression of some components of the retinal gene regulatory network, as well as disruption of genes involved in nervous system development. Results from this study, taken together with studies from other species, reveal an evolutionarily conserved role for pax6 in eye and neural specification and development.