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.

Cell-Cell Interactions in P. redivivus Ventral Hypodermal Development

P. Sternberg, B. Horvitz

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.