Worm Breeder's Gazette 14(2): 64 (February 1, 1996)
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.
HHMI and Division of Biology, 156-29, Caltech, Pasadena, CA 91125
sli-1 is a negative regulator of let-23-mediated vulval induction and encodes a protein similar to the mammalian proto-oncoprotein c-Cbl (1). Reduction-of-function (rf) mutations in sli-1 suppress the vulvaless (Vul) phenotype associated with severe reduction-of-function, but not null, mutations of let-23 (2). let-60 ras acts downstream in the signal transduction process initiated by LET-23. Initial studies have shown that sli-1 has only a weak suppression of the slight Vul phenotype associated with the let-60(rf) mutation, n2021 (2). We have furthered this study to more exactly determine how sli-1 interacts with let-60. We used four severe let-60(rf) alleles defined by Beitel et al.(3): n1876, n2022, n2034, n2035. Animals bearing any of these four let-60(rf) alleles display partial lethality as segregants from heterozygous mothers. Lethality is essentially 100 % for F2 homozygotes of these four alleles, indicating that the partial penetrance of lethality in F1 homozygotes is due to maternal rescue from the let-60(+) wild-type copy in the heterozygous mothers. We scored vulval induction in F1 homozygotes of these four let-60(rf) alleles in sli-1(+) and sli-1(rf) backgrounds. We used the sli-1(rf) reference allele, sy143. We find that sli-1(sy143) does not suppress the Vul phenotype associated with severe let-60(rf) mutations. For example, n2035 is suppressed from 0.016 induced VPCs/animal (n=62) in a sli-1(+) background to 0.034 induced VPCs/animal (n=87) in a sli-1(sy143) background. We tested whether sli-1 had any effect on the penetrance of lethality in F1 homozygotes of the four let-60(rf) alleles coming from unc-24(e138)let-60(rf)/dpy-20(e1282) heterozygous mothers in both sli-1(+) and sli-1(sy143) backgrounds. We find that sli-1(sy143) strongly suppresses the lethality associated with the F1 homozygotes of the four let-60(rf) alleles, n1876, n2022, n2034, and n2035. For example, sli-1(sy143) increased the survival of F1 n2035 homozygotes to 86 % from the 20 % F1 survival in a sli-1(+) background. However, lethality is still 100 % for F2 homozygotes in a sli-1(sy143) background. This indicates that sli-1's suppression of F1 homozygote lethality is an enhancement of the maternal rescue by the wild-type copy of let-60 in the heterozygous mothers and that sli-1 does not suppress the lethality associated with severe let-60(rf) alleles. This is in contrast to sli-1's strong suppression of lethality associated with severe let-23(rf) mutations (2). Since sli-1 does not suppress null alleles of let-23, we generated a series of hetero-allelic let-60(rf) animals and scored for vulval induction in F1 to test whether the four let-60(rf) alleles tested above were in fact null alleles. We find that n1876, n2022, and n2035 are non-null for vulval induction. For example, n2035/n2021 hetero-allelic F1 animals have 1.6 induced VPCs/animal whereas sy127/n2021 animals have 0.8 induced VPCs/animal and sDf8/n2021 animals have 0.6 induced VPCs/animal. sy127 is a putative null allele of let-60 and sDf8 is a deficiency which uncovers let-60. In summary, our results indicate that sli-1(rf) mutations do not suppress the Vul phenotype of severe, non-null let-60(rf) mutations and therefore suggests that, in vulval induction, SLI-1's target of action lies upstream of LET-60. 1. Yoon, C. H., Lee, J., Jongeward, G. D. and Sternberg, P. W. (1995) Science 269: 1102-1105. 2. Jongeward, G. D., Clandinin, T. R. and Sternberg, P. W. (1995) Genetics 139: 1553-1566. 3. Beitel, G. J., Clark, S. G. and Horvitz, H. R. (1990) Nature 348: 503-509.