The AC/VU decision provides a simple model system to study lateral specification during development (reviewed in 1). Two cells of the somatic gonad, Z1.ppp and Z4.aaa, have equivalent developmental potential in that either one may become the anchor cell (AC) or a ventral uterine precursor cell (VU). LAG-2, a ligand of the DSL family, and LIN-12, a receptor of the LIN-12/Notch family, mediate interactions between Z1.ppp and Z4.aaa so that only one AC is formed. Genetic mosaic analysis and expression studies have suggested that at least two feedback loops operate during the AC/VU decision (2,3). Specifically, before the decision both Z1.ppp and Z4.aaa express
lin-12 and
lag-2. As the decision progresses
lin-12 transcription becomes restricted to the presumptive VU whereas
lag-2 transcription becomes restricted to the presumptive AC (3). We are interested in studying other genes which may be involved in these feedback loops. One such gene is
hlh-2, which codes for a bHLH transcription factor homologous to daughterless in Drosophila and to mammalian E proteins (4). We find HLH-2 expressed in the presumptive anchor cell beginning at a time prior to a change in either
lin-12::lacZ or
lag-2::lacZ expression, suggesting that the AC/VU decision has not yet occurred. We are further analyzing the role of
hlh-2 via RNAi as well as various transgenic approaches. 1. I. Greenwald, Genes & Development 12, 1751-1762 (1998). 2. G. Seydoux, and I. Greenwald, Cell 57, 1237-1245 (1989). 3. H. A. Wilkinson, K. Fitzgerald, and I. Greenwald, Cell 79, 1187-1198 (1994). 4. M. Krause, M. Park, J-M Zhang, J. Yuan, B. Harfe, S-Q Xu, I Greenwald, M. Cole, B. Paterson and A. Fire. Development 124, 2179-2189 (1997).