The expression of a caudal homologue in a mollusc, Patella vulgata.

We cloned and analyzed the expression of a caudal homologue (PvuCdx) during the early development of the marine gastropod, Patella vulgata. PvuCdx is expressed at the onset of gastrulation in the ectodermal cells that constitute the posterior edge of the blastopore, as well as in the paired mesentoblasts, the stem cells that generate the posterior mesoderm of the trochophore larva. During larval stages, PvuCdx is expressed in the posterior neurectoderm of the larva, as well as in part of the mesoderm. This is the first report of the expression of a caudal gene in a lophotrochozoan species. The striking similarities with the expression of caudal in other organisms, such as chordates, suggest that a posterior expression of caudal is ancestral to Bilateria.