SAVAGE, R.M.*; MEIKLEJOHN, D.A.: hunchback Homologues in Annelids.
We are interested in how body plans are patterned and have focused on characterizing homologues to the Drosophilagap gene hunchback (hb) in two annelid classes. The hb gene encodes a C2H2 zinc-finger transcription factor that plays a pivotal role in fly pattern formation. We are using a cross-species antibody to compare the expression patterns of hunchback-like proteins in both leeches (Helobdella) and polychaetes (Capitella). Hb-like protein is expressed in the micromeres (and its epithelial derivatives), the gut and the nervous system in both classes, and the class-specific differences in expression correlate with changes in life history. Comparative studies between dipteran insects, nematode and annelid hbexpression domains suggest there are at least two phases of shared hb function: an embryonic and organogenic phase. In the embryonic phase, hb is expressed in cells undergoing proliferation such as the epithelial cells that also undergo morphogenetic movements. In the organogenic phase, hb is expressed in differentiated neurons of the VNC and the peripheral nervous system. Together the hb expression patterns in annelids and nematodes suggest that they do not participate in anteroposterior (AP) pattern formation in an analogous way to that of the hbin flies. This specific function apparently originated within the insect lineage. However the data does not preclude the possibility that hbhomologues outside of insects adopted other patterning functions. This research is supported by NIH grant (HD-57778) to RMS.