Worm Breeder's Gazette 13(5): 20 (February 1, 1995)

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.

lin-31, A Transcriptional Regulator of Vulval Development, Is Expressed in Vulval Precursor Cells and Is Downregulated By the Anchor Cell Signalling Pathway.

Patrick Tan, Stuart K. Kim

Dept of Developmental Biology, Stanford University Medical Center, Stanford, CA94305

During vulval development, a signal from the anchor cell
causes nearby Pn.p cells (P5.p, P6.p and P7.p) to adopt
induced vulval cell fates. Pn.p cells far from the anchor
cell (P3.p, P4.p and P8.p) do not receive the anchor cell
signal and consequently remain uninduced.
The lin-31 gene encodes a member of the HNF-3/fkh class
of transcription factors. Iin-31 is involved in the proper
establishment of both the induced and uninduced vulval
cell fates since lin-31 null mutants exhibit both an incompletely
penetrant multivulva (Muv) and vulvaless (Vul) phenotype.
Analysis of lin-31 mosaic animals indicates that lin-31
acts in the Pn.p cells (Miller et al, WBG 13.1 p72). Genetically,
the Muv phenotype of lin-31 is epistatic to the Vul phenotype
of all of the signalling genes tested, including the MAP
Kinase homolog mpk-l/suJ-l (M. Lackner, personal comrnunication).
Since LIN-31 acts in the vulval precursor cells downstream
of MPK-1 /SUR-1, it is a good candidate to be a transcriptional
response element in the anchor cell signaling pathway.
Iin-31 is apparently expressed in the Pn.p cells since
a lin-31-GFP reporter gene shows strong expression in
P3.p-P8.p beginning in L2 larvae. This expression pattern
persists until vulval induction begins. This result suggests
that LIN-31 is expressed at the right time and in the right
place to respond to the anchor cell signalling pathway.
We found that lin-31 expression was regulated by the process
of vulval induction itself. We observed that even before
P3.p-P8.p had begun to divide, lin-31-GFP expression
disappeared in cells adopting induced fates (P5.p, P6.p
and P7.p and their descendants), but persisted in cells
adopting the uninduced fates (P3.p, P4.p, and P8.p and
their progeny cells). We next observed the expression
pattern of lin-31-GFP in mutants where all the Pn.p cells
adopt either uninduced (lin-7) or induced cell fates (lin-15,
let-60(gf). In lin-7 animals, GFP expression was maintained
in all the Pn.p cells and their descendants, indicating
that activation of the anchor cell signaling pathway is
necessary for downregulation of lin-31 expression. Conversely,
in lin-15 or let-60(gf) mutants, GFP expression was repressed
in all the Pn.p cells after vulval induction had begun,
indicating that activation of the anchor cell signaling
pathway is sufficient to repress lin-31 expression.
Previous work on other HNF-3/fkh family members suggested
that these transcription factors can regulate their own
expression. To investigate lin-31 autoregulation, we
studied the expression pattern of lin-31-GFP in lin-31
mutants and observed cases in which P6.p (despite being
induced) nevertheless still expressed GFP. These results
suggest that the lin-31 gene product can act, directly
or indirectly, to negatively regulate its own expression.
In order to confirm these (and the above mentioned) results,
we plan to extend these observations using LIN-31 antibodies
or RNA in-situ hybridization.
We are currently studying whether repression of lin-31
expression is functionally important for vulval development.
We will determine whether persistent lin-31 expression
from a heat-shock promoter is able to perturb vulval development.
These results should provide a better insight into how
cell signalling controls cell fates during vulval development.