Worm Breeder's Gazette 9(1): 60
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.
The gene lin-12 III is involved in specifying the fates of at least nine pairs of non-identical lineally homologous cells in C. elegans. For each of these pairs of cells, null alleles of lin-12 cause a transformation in cell fates such that both cells express the fate normally associated with one of the pair, while dominant alleles generally cause the reciprocal transformation (Greenwald et al., 1983). We have been attempting to identify genes that interact with lin-12 in specifying cell fates. Specifically, we reverted a lin-12 dominant (lin-12(d)) allele for its egg-laying (Eg1) defect. lin-12(d) animals lack an anchor cell because the anchor cell has been transformed to a ventral uterine precursor cell. Since the anchor cell is required for the formation of a vulva (Kimble, 1981), a lin-12(d) animal lacks a vulva and cannot lay eggs. Thus, one way to suppress a lin-12(d) allele for its egglaying defect would be to restore the anchor cell. We expected to isolate mutations that reduce lin-12 gene activity using this scheme, since a reduction of lin-12 gene activity is known to be able to restore the anchor cell in lin-12(d) mutants (Greenwald et al., 1983). Hermaphrodites carrying a lin-12(d) allele (either n302 or n177) were mutagenized with EMS, and both the F1 and F2 progeny screened for the ability to lay eggs. From this screen we identified over 40 intragenic revertants and eight extragenic suppressor mutations that define at least four genes. Mutations in one of these genes, sup-17 I, result in relatively highly penetrant suppression, and we have studied these mutations in the most detail. To date there are five alleles of sup-17. Three alleles (n316, n1258, n1260) were isolated by reversion of lin12(d) alleles (as described above), and two others ( n1305 and n1306) were isolated in a complementation screen against n1258 for suppression of a lin-12(d) allele. Mutations in sup-17 appear to be allele and tissue nonspecific suppressors of lin-12(d) mutations. Specifically, the sup-17 alleles n316, n1258 and n1260 each suppress at least four different lin-12(d) alleles. In addition, the effects of these three sup-17 alleles on six different lin-12(d) phenotypes (five cell fate transformations and reduced brood size) have been examined, and suppression has been observed in each case (our observations; P. Sternberg, personal communication). In the lineages examined in detail, sup-17 mutations restore the wildtype cell lineage to lin-12(d) mutants (anchor cell, hermaphrodite P(3-8).p, and male P(9-11).p). The suppressor effects of sup-17 mutations suggest that they strongly reduce the level of lin- 12 gene activity in all tissues in which lin-12 acts. In addition to their suppressor phenotype, sup-17 mutants (whether lin-12(+) or lin-12(d)) display phenotypes not associated with any lin- 12 mutant: sup-17 hermaphrodites are slightly Dpy and have a deformed ( although functional) vulva, and sup-17 males are Dpy and have a blunt deformed tail. These observations suggest that sup-17 has some function in addition to its interaction with lin-12. Furthermore, we believe the null phenotype of sup-17 is maternal effect embryonic lethal, unlike the lin-12 null phenotype (which is late larval arrest). First, from a cross between sup-17(n316)/+ males with nDf24/+ hermaphrodites (nDf24 deletes sup-17), the n316/nDf24 progeny were viable but segregated only n316/n316 progeny, indicating a lethal phenotype of n316/nDf24 with maternal rescue. Second, sup-17(n1258) is a maternally rescued temperature-sensitive (ts) lethal allele with a late embryonic arrest phenotype. To determine the time of action of sup-17 in the determination of the anchor cell lineage, we performed temperature-shift experiments with the ts sup-17 allele n1260, measuring suppression of the anchor cell defect of lin-12(n302) (not itself significantly ts). We found that the temperature sensitive period (TSP) for sup-17 action in this lineage is in the early L2 stage, which coincides with the time of action of lin-12 (Greenwald et al., 1983) and the time at which anchor cell fate is normally determined (Kimble, 1981). Similarly, we tested the TSP for embryonic lethality with the ts lethal sup-17 allele n1258 (in lin-12(+) background). We found that the TSP is early in embryogenesis (within the first 5 hours on the 20 C time scale). These results suggest that sup-17 plays a role in the determination of the anchor cell fate, and presumably plays a similar role in the determination of most or all of the other cells that lin-12 affects. Furthermore, sup-17 has some additional function during early embryogenesis that is coordinately mutable with its lin-12 related function.