Developmental biology: LIN-12/notch activation leads to microRNA-mediated down-regulation of Vav in C. elegans

Cell-cell interactions and cross-talk between signaling pathways specify Caenorhabditis elegans vulval precursor cells (VPCs) to adopt a spatial pattern; a central "1°" VPC, in which epidermal growth factor receptor (EGFR)-mitogen-activated protein kinase (MAPK) activity is high and LIN-12/Notch activity is low, flanked by two "2°" VPCs, in which LIN-12/Notch activity is high and EGFR-MAPK activity is low. Here, we identify a microRNA gene, mir-61, as a direct transcriptional target of LIN-12 and show that expression of mir-67 promotes the 2° fate. We also identify vav-1, the ortholog of the Vav oncogene, as a target of mir-61, and show that down-regulation of VAV-1 promotes lin-12 activity in specifying the 2° fate. Our results suggest that lin-12, mir-61, and vav-1 form a feedback loop that helps maximize lin-12 activity in the presumptive 2° VPCs.