Worm Breeder's Gazette 12(2): 97 (January 1, 1992)

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 acts late in the vulval development pathway

Barbara Anne Morisseau, Stuart K. Kim

Department of Developmental Biology, Stanford University Medical Center, Stanford, CA 94305

We have been studying how lin-31 acts to specify vulval cell fates. lin-31 mutants display a deregulated phenotype in vulval development; any of the six Pn.p cells (P3.p-P8.p) may adopt any of the three vulval cell fates (1°, 2°, or 3°). For instance, in one animal P7 .pwas observed to express a 3° fate though it was in close proximity to the anchor cell while P8 .padopted a 2° cell fate even though it was farther away from the anchor cell. In addition, adjacent Pn.p cells can each adopt a 1° cell fate, suggesting that the lateral signalling pathway, whereby a 1° Pn.p cell prevents its neighbors from also adopting a 1° cell fate, is defective. Therefore, lin-31 is an integral component in the specification of all three cell fates and is required for the determination of all six Pn.p cells.

Our proposal that lin-31 has distinct functions in specifying three alternative cell fates is different from models explaining the function of other vulval determination genes, such as those with a vulvaless loss-of-function phenotype (Vul genes) or a multivulva loss-of-function phenotype (Muv genes). The Vul and Muv genes are thought to act as on/off switches that either activate or repress the anchor cell and hypodermal signalling pathways that control Pn.p cell fate. In lin-31 mutants, Pn.p cell fates may become deregulated because all Pn.p cells lack proper lin-31 regulatory functions.

Our studies indicate that lin-31 appears to act at a late step in the anchor cell signalling pathway. First, the anchor cell was ablated with a laser in lin-31 mutants and 1° and 2° cell fates were still expressed. This result indicates that lin-31 cannot act only in the anchor cell, and suggests that lin-31 is required at a step following the production of the anchor cell signal.

Second, lin-31 has been placed in the vulval developmental pathway using genetic epistasis experiments. Double mutants were constructed with lin-31 ( n1053 )and any one of five Vul mutants: lin-2 ( e1309 ); lin-7 ( e1413 ); lin-10 ( n1390 ); let-23 ( n1045 );and let-60 ( n1531 dn)/+.All five double mutants display the lin-31 deregulated phenotype. Pn.p cells can express 1° and 2° cell lineages in a variable way in the lin-31 ;Vul double mutants as determined using direct observation with Nomarski microscopy or by staining with FITC-labelled concanavalin A, a marker for 1° and 2° cell lineages (G. Freyd, personal communication). Because we feel we are studying a regulatory pathway, we place lin-31 downstream of lin-2 , lin-7 , lin-10 , let-23 ,and let-60 in the anchor cell signalling pathway. It is particularly interesting that lin-31 is downstream of let-60 ,a ras homologue. The lin-31 gene product could be a substrate of let-60 or could be acting farther downstream.