Duplicated Pax6 Gene Expression During Nervous System Development in the Asexually Reproducing Annelid Nais communis

<i>Pax6</i> plays a highly conserved role in the formation of the eye, development, and patterning of the nervous system across bilaterians. Nevertheless, there are no studies focusing on the role of <i>Pax6</i> during asexual reproduction, a developmental trajectory that is widespread among metazoans. The present study represents the first investigation of <i>Pax6</i> gene expression during agametic propagation in annelids. We identified in the asexually reproducing annelid <i>Nais communis</i> four homologs of <i>Pax6</i> and examined their developmental patterns by in situ hybridization. To establish a morphological basis for the expression patterns, we used immunohistochemistry and confocal laser scanning microscopy to describe the nervous system architecture of the growing adults and remodeling of the original ventral nerve cord, development of the new brain, ventral ganglia, peripheral nerves, and sensory organs in asexually reproducing worms. Our results support the hypothesis of an evolutionarily conserved function of <i>Pax6</i> genes in the development of the eye and other sensory organs, as well as the central nervous system, among bilaterians, regardless of developmental trajectory. On the other hand, identified <i>Pax6</i> homologs show differential expression within the developing new head and tail ends. Differences in spatiotemporal expression patterns may be evidence of functional diversification of duplicated homologs.