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.

A Signal Between Pn.p Cells During Vulval Development

P. Sternberg

Figure 1

Figure 2

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]

Figure 1

Figure 2