Figure 2.
lin-39 is expressed in an AC and Ras dependent gradient in the VPCs. (A) Wild-type larva, showing strong LIN-39 antibody staining in P6.p and weaker staining in the VPCs to either side. Staining in the neurons of the ventral cord can also be seen (small nuclei between the VPCs). (B)
dig-1(
n1321) larva. In
dig-1 mutants, the gonad often shifts to the anterior, thereby causing anterior vulval induction. In this animal the gonad was centered over P4.p, the cell expressing
lin-39 most strongly. (C) Wild-type larva in which the somatic gonad precursor cells, Z1 and Z4, have been ablated; these animals have no AC and are therefore not able to induce a vulva. In animals with no AC, the LIN-39 antibody staining is reduced in P6.p. (D)
lin-3(
n378) mutant showing weaker expression in the VPCs, especially P6.p, as compared to wild type. The AC induces the vulva via an EGF-like ligand encoded by the
lin-3 gene. Similar staining was seen in
let-23(
sy97) mutant animals, which have a mutation in the EGF-receptor gene (data not shown). (E)
lin-1(
e1026) mutant larva showing increased expression in the VPCs.
lin-1 encodes an ETS-like transcription factor which inhibits vulval induction. Similar staining was seen in two other strains with activated Ras pathways:
lin-15(
n309) and
let-60-ras
(n1046gf)(data not shown). About 50% of AC-ablated and signaling-defective larvae show a weak gradient of LIN-39 across the VPCs (the very high levels of LIN-39 seen in wild-type animals are never seen in these mutants). This suggests that there may be a Ras-independent mechanism for biasing
lin-39 expression in the VPCs. *Indicates approximate AC position.