FR�BIUS, A.C.*; SCHWAB, R.L.; SEAVER, E.C.; University of Hawaii at Manoa; University of Hawaii at Manoa; University of Hawaii at Manoa: Expression of Hox and ParaHox genes during development of the polychaete annelid Capitella sp. I

In recent years Hox genes have been isolated from most animal phyla. These genes are clustered in vertebrates and flies and their spatial and temporal expression along the anterior-posterior body axis reflects the structural organization of the cluster. Hox genes do not code for specific morphological structures, they are regarded as key players in body plan regionalization. Another cluster also showing temporal and spatial colinearity is the ParaHox cluster, a paralogue of the Hox cluster. Little is known about the cluster structure of Hox and ParaHox genes in the �lophotrochozoan� phyla and in many cases expression data of the entire Hox cluster is still incomplete. Focusing our efforts on the largely homonomous and more direct developing polychaete Capitella sp. I, we have succeeded in isolating full-length transcripts of ten Hox and three ParaHox genes and analysed their expression during larval and juvenile development. Expression of ParaHox genes has not been well characterized in Lophotrochozoans and our results show that their expression appears to be conserved with distantly related taxa such as Chordates. The spatio-temporal Hox expression is consistent with a role in body plan regionalization. In contrast to Hox gene expression in the leech Helobdella and some Chaetopterus Hox genes, most Hox genes in Capitella sp. I show distinct posterior boundaries with expression domains spanning only a few segments. Expression involves varying ventral and lateral cell populations and is not restricted to the CNS. In addition, this study extends the examination of embryonic and larval Hox gene expression in annelids to include analysis of expression in juveniles.