Worm Breeder's Gazette 14(4): 53 (October 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.
Waksman Institute, Rutgers University, Piscataway, NJ 08855
We have previously described our analysis of a TGF-b pathway regulating body size in C. elegans. This pathway includes the TGF-b type II receptor DAF-4, the type I receptor SMA-6, and the homologous downstream components SMA-2, SMA-3, and SMA-4. We continue to be interested in identifying novel components of this signaling pathway. To this end, we have been conducting a series of genetic screens. Here we present an update on two of these screens. I. The Small Screen At least four TGF-b signaling components have been identified by their Small phenotypes: the downstream components encoded by sma-2, sma-3, and sma-4, and the type I receptor gene sma-6. To identify other components of the pathway, it seemed reasonable to begin by isolating Small mutants, since this type of screen had not been done systematically before. We therefore screened F2 progeny of EMS-mutagenized N2 worms, and isolated 85 Small mutants from ~17,000 mutagenized genomes. We are characterizing these mutations by first doing a complementation test with the triple mutant sma-4 sma-3 sma-2. Alleles that complement this chromosome are being mapped to chromosomes by STS mapping, using described Tc1 polymorphisms. Then, these alleles are being placed into complementation groups. Fine structure mapping, analysis of male tail phenotypes, and eventually molecular characterization will follow. Alleles that fail to complement known genes include: 2 alleles of sma-1, 38 alleles of sma-2, sma-3, or sma-4, and 1 allele of sma-6. An additional 20 alleles have been mapped to chromosomes and are being placed into complementation groups. II. Suppressors of sma-6 Mutations in sma-6 presumably result in a loss of signaling activity of the type I receptor in the pathway and hence yield the small phenotype. The CB1482 sma-6 strain was screened for suppressors in the pathway, which were identified by wild-type or long phenotypes. The reasoning behind the screen was derived from two possibilities. First, components downstream of the receptor in the pathway, when constitutively active, may be able to circumvent the requirement for full sma-6 receptor signaling potential and thereby restore transduction. In addition, negative regulators of the pathway, when mutant, may revert small animals via higher signal throughput. It is reasonable to argue that mutations which augment the level of signaling in the pathway would be easier to generate against a weak mutant background. Therefore, the CB1482 (obtained from the CGC) strain was used because it is a relatively mild sma-6 mutant biochemically and phenotypically. However, a practical consideration to this approach is the increased difficulty in the identification of suppressed animals. We screened through approximately 19k genomes and obtained nine suppressors, which we are currently mapping and characterizing. Additionally, we are performing the screen with a stronger allele of sma-6.