LEE, P.N.*; CALLAERTS, P.; HARTMANN, B.; FARFAN, C.; MARTINDALE, M.Q.; DE COUET, H.G.: Hox Gene Expression in the Sepiolid Squid, Euprymna scolopes

Cephalopods represent a highly derived group within the Mollusca. They have evolved extensive alterations in the basic molluscan body plan, including a reduction or loss of the shell, novel recruitment of the mantle for locomotion, and modification of the foot into a crown of prehensile arms surrounding the head. However, the most striking modifications are those involving the anterior-posterior (AP) and dorsal-ventral (DV) axes. In cephalopods, the visceral mass has undergone extensive elongation along the DV axis, while the body along the AP axis has been greatly compressed. As a result, the functional AP axis corresponds to the embryonic DV axis. To understand how morphological changes relative to the body axes have arisen in cephalopods, we examined Hox genes in the sepiolid squid, Euprymna scolopes. Hox genes are expressed along the AP axis in nested domains in bilaterians. As a result, they can be used as highly conserved molecular markers specific for the AP body axis. Using RACE-PCR, we have cloned nine Hox orthologues from E. scolopes, and used these clones as probes for in situ hybridizations to examine their spatial patterns of expression during development. Preliminary results suggest that the nested expression patterns of Hox genes may be conserved in some regions along the embryonic AP axis during cephalopod development.