Worm Breeder's Gazette 7(1): 47
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.
In C. elegans the gonad, specifically the anchor cell, induces the ventral hypodermal precursors P(5-7).p to generate the vulva (Kimble, Develop. Biol. 87, 286, 1981). Ablation of any of these vulval precursor cells leads to regulation (Sulston and White, Develop. Biol. 78, 577, 1980). Similar regulation is seen in C. elegans males. We have performed a series of gonadal, P, and Pn.p cell laser ablation experiments in P. redivivus females and males. In P. redivivus, P(5- 8).p generate the vulva; the other Pn.p cells join the hypodermal syncytium. [In C. elegans, P(3,4,8).p divide and their progeny join the syncytium; P(1,2,9-11).p join the syncytium directly.] Our results can be summarized as follows. (1) The P. redivivus gonad is required for female Pn.p divisions and vulval development. The anchor cell (Z4. aaa) is required for the third round of Pn.p divisions. Z4 is required for vulval induction, although a few Pn.p cells can divide in its absence. In males of both species the gonad is not required for Pn.p divisions. (2) Regulation occurs as in C. elegans: the ablation of certain Pn.p cells can result in the replacement of the ablated cell by another Pn.p cell. (3) As in C. elegans, there is a hierarchy of replacements. A higher ranked cell can be replaced by a lower ranked cell but will not replace a lower ranked cell. In C. elegans hermaphrodites, the fate of P6.p is primary (ranks highest in the hierarchy), the fates of P(5,7).p are secondary, and the fates of P(3,4,8).p are tertiary. In P. redivivus females, the fates of P(6,7) .p are primary, the fates of P(5,8).p are secondary, and the fates of P(4,9).p are tertiary. (4) In C. elegans hermaphrodites, P(3-8).p can participate in vulval development and thus define the vulval equivalence group. In P. redivivus females, at least P(4-9).p can participate in vulval development. Thus, the vulval equivalence group differs between the species. (5) In males of both species, P10.p and P11.p generate cells of a pre-anal sensillum (called the hook sensillum in C. elegans); P9.p joins the ventral hypodermal syncytium or, in some C. elegans males generates two daughters that join the syncytium. As in C. elegans, P9.p can replace P10.p. Thus, in P. redivivus, P9.p belongs to both the male and female equivalence groups, indicating that equivalence groups in the two sexes need not be distinct. The differences in vulval regulation between the two species suggest that there are at least four independent levels of control specifying Pn.p fate in vulval development. Different sets of instructions seem to specify: (a) which Pn.p cells can participate in vulval development; (b) which Pn.p cells do participate in vulval development; (c) which Pn.p cells follow primary or secondary fates; and (d) what lineage is generated by cells with the primary, secondary and tertiary fates.