Figure 1

Formation and specialization of the vulval cells during the first hours of development of C. elegans . Larval phase L1: 0 h) After eclosion, the worm has two rows of P cells in the middle ventral region. 10 h) The rows merge. Larval phase L2: 12 h) The cells P1-P12 undergo a longitudinal division, the anchor cell forms (brown oval), and P3.p-P8.p become vulval precursor cells (VPCs). 25 h) P6.p responds to LIN-3/EGF secreted by the AC and acquires the primary fate (red), this cell secrets the DSL ligands that constitute the lateral signal. 28 h) P5.p and P7.p respond to the lateral signal of P6.p, thus acquiring the secondary fate (yellow). The rest of the VPCs acquire the tertiary fate forming the pattern 3^rd3^rd2^nd1^st2^nd3^rd. Larval phase L3: 30 h) Cells P3.p to P8.p divide longitudinally, and the daughters of the secondary fate cells are polarized. 32 h) The descendants of the tertiary fate cells fuse with hyp7 and the rest divide longitudinally once more, and the most proximal granddaughters of P6.p are induced again by the anchor cell (AC). Larval phase L4: 36 h) Formation of the adult vulval cells: some descendants of the VPCs divide a third time with the pattern LLTN TTTT NTLL. L stands for a lateral division, forming anterior and posterior daughters. T is a transverse division, forming left and right daughters. N stands for no division. Cells are classified, in proximal to distal order as vulF (red), vulE (orange red), vulD (orange), vulC (yellow), vulB2 and vulB1 (green yellow), and vulA (green).