Fig. 3. (A) 1408 bp-long genomic fragment from the first intron is capable of driving
lin-12 expression in the vulval precursor cell lineages. A,
lin-12(1in_1408)::gfp (gfp is driven by the first intronic fragment of
lin-12) expression in a twofold stage embryo (two focal planes; glowing cells are indicated by arrows) and at the L1, L2 and L3 stages. In an L1 larva,
lin-12(1in_1408) is active in most Pn.p blast cells (posterior descendants of P blast cells; arrows). At the early L3 stage, the six centrally located Pn.p cells, P(3-8).p, also called the vulval precursor cells (VPCs), display a differentiated
lin-12(1in_1408) expression pattern. Vulval induction occurs by this time. In P5.p and P7.p,
lin-12(1in_1408) is expressed more intensively than in other VPCs. At the mid L3 stage, the P(3-8).p cells divide once, producing a posterior and an anterior descendant. Characteristic pattern of
lin-12(1in_1408) expression proceeds at this stage: the P5.p and P7.p daughters strongly express
lin-12(1in_1408), as compared with other VPC daughters. At the late L3 stage, this characteristic pattern of
lin-12(1in_1408) expression is still evident in the P(3-8).p lineages. (B) Expression of
lin-12(1in_1408) is obvious in two somatic gonadal cells. From the L2 stage,
lin-12(1in_1408) is transcriptionally active in the presumptive anchor cell (AC) and a ventral uterine precursor (VU) cell (indicated by the yellow arrow and the orange arrow, respectively). At the late L3 stage,
lin-12(1in_1408) expression remains in the presumptive VU cell, but not in the AC, as a result of lateral induction (Wilkinson et al., 1994). Only P5.p-P7.p are indicated from the VPCs. (C)
lin-12(1in_1408) expression in the vulval tissue at the L4 stage. By the late L4 stage, only the P5.p and P7.p descendants express
lin-12(1in_1408). At the bottom, an L4 stage vulva tissue with the characteristic Christmas-tree structure. The corresponding fluorescent picture is to the left. (D) Expression of
lin-12(1in_1408) at the adult stage is highly reduced. As a result of background expression, only a few unidentified cells (small arrows) in the tail region express
lin-12(1in_1408). Both anterior and middle body regions lack fluorescence. The arrowhead points to the vulva, the large arrow shows two adjacent cells with strong background expression.