Several loci involved in the Daf/Sma TGF-beta-like signal transduction pathway have been identified, including the type II receptor gene
daf-4 and the C. elegans Smad gene family members
sma-2-4. Extant alleles are recessive and confer pleiotropic phenotypes which include small body size. In contrast, over-expression of a
sma-4 transgene confers a low-penetrance Lon phenotype (S. Baird, unpublished). Dominant, hypermorphic mutations of loci of the Daf/Sma pathway might result in a Lon phenotype similar to those observed in
sma-4,6 transgenic strains. In order to identify dominant alleles of new and existing genes that are involved in Daf/Sma signalling, we have screened 2.5 x 106 EMS-mutagenized haploid genome equivalents in an F1 screen for dominant Lon and/or Sma hermaphrodites. One dominant Lon (
lc5) and four dominant Sma mutants (
lc4,
lc6,
lc7, bdX) have been recovered.
lc5 and
lc6 have been mapped by PCR-based STS mapping between mutant (N2) strains and DP13 and/or standard three-factor crosses.
lc5 is located between
unc-24 (+3.58 mu) and sP4 (+5.33 mu) on LGIV, and
lc6 is located between
stP103 (-1.33 mu) and
stP129 (+2.04 mu) on LGX. To confirm that these alleles identify new loci involved in the Daf/Sma signal transduction pathway, we are screening mutagenized
lc5 and
lc6 strains for revertants, and we are characterizing the dominant phenotypes.