Fig. 1.

mir-61 is a direct target of LIN-12 in presumptive 2° VPCs. (A) An inductive signal from the anchor cell (AC) of the gonad activates EGFR-MAPK signaling primarily in P6.p, and a lateral signal from P6.p activates LIN-12 in P5.p and P7.p. The descendants of the 1° and 2° VPCs form the vulva, and the progeny of 3° VPCs fuse with the hypodermal syncytium. We used the 1° fate marker arIs92[egl-17p::cfp-lacZ] (3), the 2° fate marker nIs106[lin-11p::gfp] (21), and the 3° fate marker arIs101[K09H11.1p::yfp] (22). (B) mir-61 is expressed in P5.p and P7.p. The mir-61 promoter contains two LBSs that are conserved in the C. briggsae ortholog of mir-61 (5). A reporter containing 1 kb upstream of mir-61 fused to YFP is expressed in P5.p and P7.p (22) and their daughters (shown here). Prominent expression in cells of the gonad in which LIN-12 is active is also seen. (C) LBSs are required for mir-61 expression in P5.p and P7.p. Two LBSs (YRTGRGAA) (3, 23) that are conserved in C. briggsae were mutated to YRAGRGAA; a third nonconserved sequence, RTGGGAA, was also mutated to RAGGGAA. In three individual lines analyzed, expression of YFP in P5.p and P7.p disappeared. Expression in cells in which lin-12 is not known to play a role in cell fate specification was normal, but gonadal expression was also abolished.