Worm Breeder's Gazette 10(1): 107
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
According to the simplest model for pattern formation during vulval development, the inductive signal from the anchor cell is graded and directly stimulates Pn.p cells to be 1 or 2 , depending on their distance from the anchor cell [Cell 44:761(1986)]. In this view, anchor cell-proximal Pn.p cells prevent more distal Pn.p cells from receiving a high level of signal simply by being in the way. I have now obtained evidence that 1 cells prevent adjacent cells from also becoming 1 . In lin-15 Multivulva hermaphrodites, all six Pn.p cells are 1 or 2 . In no case are adjacent cells 1 (0/43 pairs), while adjacent cells often are 2 (14/43 pairs). These observations suggested that a 1 cell prevents its neighbors from being 1 . To test this hypothesis, I destroyed by irradiation from a laser microbeam the gonad and P(3,4,5,6,8).p from six lin-15 hermaphrodites. In all six animals, P7.p was 1 . By contrast, in four animals lacking a gonad but with all six Pn.p cells intact, P7.p was 2 . I conclude that the 'ground state' of a Pn.p cell in a lin-15 animal is to be 1 , and that if a neighboring cell is 1 , a Pn.p cell will become 2 . This result holds so far for at least some other Pn.p cells in lin-15 animals, and in lin-8; by genetic ablation. [See Figure 1] I have also examined lin-15 animals with two Pn.p cells: if two Pn.p cells are touching, one is 1 and one is 2 ; if two Pn.p cells are not touching, both are 1 . Thus, the inhibitory signal from a 1 cell to its neighbors might be mediated by direct cell-cell contact. Since lin-12 is necessary for 2 cell fates in lin-15 animals (all six Pn.p cells are 1 in a lin-12(0); utant), lin-12 may play a central role in this cell-cell contact inhibition, a role not inconsistent with the structure inferred by Greenwald et al. [1987 CSH Mtg].. The precision of the pattern formation process during vulval development may result from the combined action of two intercellular signals: a graded signal from the anchor cell differentially affecting 1 and 2 cells, and a signal from 1 cells to 2 cells inhibiting them from becoming 1 and/or stimulating them to become 2 . [See Figure 2]