A PCR-BASED SURVEY OF HOMEOBOX GENES IN CTENODRILUS-SERRATUS (ANNELIDA, POLYCHAETA)

The polychaete worm Ctenodrilus serratus was surveyed for the presence of HOM/HOX and engrailed-type homeobox genes using PCR with degenerate primers. Sixteen unique homeobox fragments were found in surveys of genomic and cDNA with three different primer sets. For three fragments, RACE was employed to obtain additional homeobox sequence and the 3' flanking region. Nine HOM/HOX-type fragments were identified, including putative representatives of the Hox1/lab, Hox2/pb, Hox3, Hox4/Dfd, and Antp/Lox5 cognate groups. Two additional Antp-like fragments could not be assigned specific orthology. Presence of an ortholog of leech Lox2 in addition to a Ubx/abdA-like gene suggests that independent duplications of a single precursor occurred in the annelid and arthropod lineages. No representative of the Hox9/AbdB group was identified. Our results are consistent with a hypothesis of a single HOM/HOX cluster in Ctenodrilus as extensive as that seen in strongly tagmatized arthropods, suggesting that the primitive role of these genes even in overtly metameric animals was something other than specification of overt segmental differentiation. The primers used also detected representatives of six other homeobox classes or families: Xlox(XlHbox8/HTr-A2), Ovx (Chox7), caudal, Prh (proline-rich homeobox), NEC (ceh-9/Tghbox5), and engrailed.