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.
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.