In C. elegans, the heterochronic genes
lin-4,
lin-14,
lin-28 and
lin-29, control the relative timing and sequence of many events during post-embryonic development, including the terminal differentiation of lateral hypodermal seam cells. We have been performing a variety of genetic screens aimed at identifying additional members of the heterochronic gene pathway (see related abstract, Abrahante et al.). We will present a summary of our phenotypic and genetic analyses of the mutants isolated from these screens. One additional member of the heterochronic gene pathway is
lin-42, a gene for which a single mutant allele has been reported (Liu, 1990).
lin-42(
n1089) mutants execute seam cell terminal differentiation precociously, during the L3-to-L4 molt. We have identified a number of new
lin-42 alleles in our screens and are investigating
lin-42's role in the timing of seam cell terminal differentiation.
lin-29 is epistatic to
lin-42(
n1089) (Liu, 1990) and to our new alleles. All of the alleles we have isolated are partially epistatic to
lin-4. That is, some, but not all, of the seam cells in
lin-42 lin-4 double mutants terminally differentiate during the L3-to-L4 molt, resulting in animals with gaps in their alae. These alleles exhibit variable penetrance of the mutant phenotypes and we are ordering them in an allelic series with respect to alae synthesis and suppression of
lin-4 defects. We are in the process of isolating g-ray induced alleles to describe the
lin-42 null phenotype and to aid in the cloning of the gene. We have initiated a positional cloning strategy and will present our progress toward localizing the gene on the left arm of Linkage Group II. Liu, Z. (1990). Ph.D. Thesis, Harvard University, Cambridge, MA.