MATUS, D.Q.; HALANYCH, K.M.; MARTINDALE, M.Q.; Univ. of Hawaii at Manoa; Auburn University; Univ. of Hawaii at Manoa: Axial Patterning in Chaetognaths: An Evo-Devo Look at an Enigmatic Phylum

We are interested in the evolution of axial patterning (anterior-posterior & dorsoventral) and body plan formation throughout the Metazoa. We have used PCR (Polymerase Chain Reaction) to isolate developmental regulatory genes involved in axial patterning from the pelagic chaetognath, Flaccisagitta enflata. These include 8 members of the Hox family and a ParaHox gene, as well as genes possessing homology to decapentaplegic (dpp) / bone morphogenetic protein 2/4 (BMP2/4) and short of gastrulation (sog) / chordin. We are examining the expression of these genes via in situ hybridization to investigate both conserved and novel patterns of expression throughout development. Chaetognaths, or arrow worms, are marine animals that are ubiquitous and abundant members of oceanic zooplankton communities, yet their phylogenetic position within the Metazoa has remained enigmatic since Darwin�s time. They possess a suite of morphological and developmental characters that have made resolving their phylogenetic affinity within the Metazoa difficult utilizing traditional methodologies. However, recent molecular evidence from structural and developmental regulatory genes suggests that they may occupy a basal position within the protostomes. Yet the presence of many deuterostome-like characteristics (holoblastic radial cleavage, enterocoely, a tripartite coelomic arrangement, a post-anal tail, and a presumed posterior fate of the blastopore) suggests that their origins may lie prior to the protostome/deuterostome divergence. The study of developmental regulatory genes within this potential basal bilaterian will shed new light onto the evolution of animal body plans and axes formation at the base of the Bilateria.