Rhomboid is sufficient to mediate the complete oenocyte identity function of abdominalA. A.P. Gould , V. Brodu , P.R Elstob. MRC National Inst Medical Res, London, England.

   One of the ways that Hox/homeotic genes generate segmental diversity is by promoting the differentiation of segment-specific cell types. To begin dissecting this process, we are studying how abdominalA specifies the larval oenocyte. Previously, we defined the embryonic origin of oenocytes (Elstob et. al. 2001, Development 128, 723-732). They are induced from the dorsal ectoderm by a signal emanating from the forming PNS. More specifically, Spitz ligand, secreted by one underlying primary chordotonal organ precursor (COP), activates the EGFR in the responding ectoderm, triggering the induction of an oenocyte cluster. The zinc-finger encoding gene spalt is required in the responding ectoderm for it to adopt the oenocyte fate rather than the default COP fate. We will present new results from Hox mutant rescue assays that indicate that Rhomboid is sufficient to mediate the complete oenocyte identity function of abdominalA. In this context, AbdA does not directly control cell type but merely provides a permissive signal in the abdomen that uncovers a cryptic cell identity that is present in all trunk segments. These studies support a model where the time that cells become competent to respond to Hox-dependent signals can influence their segmental distribution.