Worm Breeder's Gazette 15(1): 56 (October 1, 1997)
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.
|1||HHMI/Biochemistry, Columbia University, 701 West 168th Street, Room 720, NY, NY 10032|
|2||Dept. of Biology, MIT 68-411, Cambridge, MA 02139|
Previous genetic analysis established that sup-17 facilitates lin-12 signalling (Tax et al., Genetics, in press). With the invaluable assistance of the genome project, we have cloned sup-17 and shown that the predicted SUP-17 protein is a member of the ADAM family of proteases (see Wolfsberg and White, Devel. Biol. 180, 389-401, 1996); in particular, SUP-17 is very similar to Drosophila kuzbanian (KUZ), which functions in Drosophila and vertebrate neurogenesis (Rooke et al., Science 273, 1227-1231, 1996; Pan and Rubin, Cell 90, 271-280, 1997) (see Figure). We have extended the genetic studies of Tax et al. (1997) by showing that sup-17 does not act downstream of lin-12. Reduction or elimination of sup-17 activity suppresses the effects of lin-12(d) mutations (see Tax et al., 1997), an allelic series of hypermorphs that result from point mutations in the extracellular domain. In contrast, we have found that reducing sup-17 activity cannot suppress mutant phenotypes associated with lin-12(intra). The lin-12(intra) transgene expresses the intact intracellular domain under the control of lin-12 regulatory sequences and behaves like a constitutively active receptor. It is incompletely penetrant for its effects on the AC/VU decision and VPC specification, and hence does not elevate lin-12 activity as much as the stronger lin-12(d) alleles. Furthermore, we have found that sup-17 can enhance the AC/VU decision defect of a partial loss-of-function lin-12 allele, implying that it does not require a lin-12(d) lesion to influence lin-12 activity. Since sup-17 can suppress lin-12(d) mutations but cannot suppress lin-12(intra), we can infer that sup-17 does not act downstream of the activated receptor. We have also found that the interaction between sup-17!and lin-12 occurs within the same cell. By using a laser microbeam to isolate Z1.ppp or a vulval precursor cell from its normal source of signal, we showed that sup-17 mutations reduce the cell intrinsic level of constitutive lin-12 activity in lin-12(d) mutants. This result suggests that sup-17 acts cell autonomously and that its action is not dependent on ligand-binding. The genetic analysis of the relationship between sup-17 and lin-12 in C. elegans complements and extends the results from genetic studies of the relationship between the Drosophila kuz and Notch genes (Pan and Rubin, 1997). SUP-17/KUZ may function in the proteolysis of LIN-12/NOTCH proteins. There is evidence for a cleavage event in the extracellular domain of C. elegans, Drosophila, and human NOTCH proteins (Christensen et al., Development 122, 1373-1383, 1994; Blaumueller et al., Cell 90, 281-291, 1997; Pan and Rubin, 1997). Furthermore, KUZ is required in vivo for the proteolytic processing of NOTCH into two fragments consistent with a cleavage event in the extracellular domain (Pan and Rubin, 1997). Further work in several systems will be directed towards understanding how proteolysis influences LIN-12/Notch activity. Special thanks to Frans Tax, Jim Thomas, Chip Ferguson and Bob Horvitz.