Regulation of hlh-2 transcription during specification of the anchor cell of the C. elegans hermaphrodite gonad.

The anchor cell (AC) of the Caenorhabditis elegans hermaphrodite somatic gonad primordium is a signaling nexus that regulates uterine and vulval development. As the somatic gonad primordium is forming, four cells, two α and two β cells, are born with the potential to be the AC. This potential becomes restricted to the α cells, which undergo the LIN-12/Notch-mediated AC/VU decision to resolve which α cell will become the AC. The transcription factor HLH-2, the sole E/Daughterless protein ortholog in C. elegans, is critical for this process, and dynamic regulation of hlh-2 transcription contributes to the robust specification of a single AC. The hlh-2prox regulatory element mediates the dynamic pattern of hlh-2 transcription: the initial expression in the parents of the α and β cells, which is briefly sustained in the α and β cells after they are born; its subsequent restriction to the α cells during the AC/VU decision; and its continued expression in the AC. In this study, we identify the cis-acting sequences within hlh-2prox and transcription factors required for the initial expression of hlh-2 in the α and β cells and their parents, demonstrate that the Wnt/β-catenin Asymmetry Pathway (WβA) regulates restriction of hlh-2 transcription to the α cells, and show that the maintenance of hlh-2 transcription in α cells requires distinct elements and the chromatin factor LSY-12. This analysis extends our understanding of regulatory mechanisms that operate during a precise and robust Notch-mediated lateral specification paradigm.