Isolation of genes involved in ascidian metamorphosis: epidermal growth factor signaling and metamorphic competence

Although embryonic development in ascidians has been studied for over a cen tury, the signals involved in coordinating post-larval development and meta morphosis are just beginning to be investigated. In this paper, we demonstr ate that transcription is necessary for. both the acquisition of metamorphi c competence and the completion of the initial events of metamorphosis in B oltenia villosa. Transcripts expressed during metamorphic competence were i solated by a suppressive PCR subtraction of Boltenia villosa larval cDNAs. One of these transcripts is homologous to cornichon. Cornichon has a crucia l but undefined role in epidermal growth factor (EGF) signaling during Dros ophila embryogenesis. In situ hybridization demonstrates that Boitenia corn ichon (Cnib) is expressed in the anterior papillary region of larvae as the y gain competence, Our hypothesis; is that Cnib acts to potentiate EGF sign aling, thereby allowing Boltenia larvae to respond to cues for metamorphosi s. Further research into the role of Cnib in urochordate metamorphosis may provide insight into the function of cornichon in other organisms. A better molecular understanding of urochordate metamorphosis will also provide a f oundation for exploring the role of metamorphosis in chordate evolution.