Figure 1

Cell lineage of the vulva. (A) Six Vulval Precursor Cells (VPCs) called P3.p to P8.p have the potential to adopt the vulval fate [47, 48]. The anterior of the animal is on the left (P3.p) and posterior on the right (P8.p). In wild type animals only three VPCs (P5.p -P7.p) will adopt the vulval fate, the other VPCs will fuse to hyp7 after first division (white circles). Sometime, P3.p fuses before the first cell division. The VPCs that are committed towards the vulval fate will undergo three rounds of cell division. The descendants after first division are named P5/6/7.px, and after second division P5/6/7.pxx, and after third divison P5/6/7.pxxx (x signify either anterior cell (a) or posterior cell (p)). Of note, two cells will not undergo the third division (see arrows). The descendants of P6.p are classified as primary cells, and express high levels of LET-23 signalling (black circle). Descendants of P5.p and P6.p are classified as secondary and express low levels of LET-23 signalling (grey circles). The lines indicate the axis of cell division, which is longitudinal for all cells up to second division. However, at third division, all the primary cells will divide in the transverse axis of cell division, as well as two cells that are descendants of P5.p and P7.p. (B, C, D and E) Depletion of cdt-2 causes excessive LET-23 signalling in secondary cells. DIC and fluorescent photos showing that egl-17::cfp is only expressed in primary cells (underlined) and not in the secondary cells (broken line) of wild type animals (B and C). However, in animals depleted of cdt-2, secondary cells (broken line) express egl-17::cfp, indicating excessive LET-23 signalling in those cells (D and E). % of animals with persistent expression of egl-17::cfp is indicated at the bottom right with the number of worms analysed.