Novel and conserved roles for orthodenticle/ otx and orthopedia/ otp orthologs in the gastropod mollusc Patella vulgata

The orthodenticle/ otx and orthopedia/ otp classes of homeobox gene families have been identified in all three major classes of bilaterians: deuterostomes, lophotrochozoans, and ecdysozoans. Otx genes have been studied extensively and play a role in the development of anterior neural structures. Otp genes have been found to be involved in nervous system development in mouse and Drosophila. To date, no members of these genes are known in molluscs. We cloned orthologs of orthodenticle/ otx and orthopedia/ otpfrom the gastropod Patella vulgata, and designated them Pv-otx and Pv-otprespectively. Our analysis of the spatio-temporal expression pattern of otx and otp orthologs during P. vulgata embryogenesis leads to the following conclusions. First, Pv-otx is expressed in and around the stomodaeum and our analysis thus supports the previously suggested conservation of the protostome and deuterostome larval mouth regions. Second, we find that Pv-otp is involved in the development of the larval apical sensory organ, suggesting a conserved role for this gene family in nervous system development. A similar conserved role in nervous system development has been proposed for orthodenticle/otx genes and we suggest that part of the cells expressing Pv-otx are involved in the development of the anterior nervous system. Last, we postulate that otx genes were ancestrally involved in the development of ciliary bands in bilaterians.