lin-29 is a C. elegans heterochronic gene that activates a temporal developmental switch in the hypodermal 'seam' cell lineage. In wild- type animals at the L4 molt, the seam cells switch from larval to adult specific fates. The seam cells exit the cell cycle, fuse together and synthesize a morphologically and biochemically distinct adult cuticle, and no further molts ensue. This developmental switch is temporally controlled by the heterochronic genes
lin-4, lin-
l4, lin- 28,
lin-29,
lin-41, and
lin-42. Of these six genes
lin-29 is the most direct regulator of the switch. In
lin-29 loss-of-function mutants, the seam cells fail to execute the switch and supernumerary larval molts occur as the seam cells continue to divide and synthesize larval cuticle. In contrast, animals triply mutant for
lin4 lin-14 and
lin-28, but wild type for
lin-29, do execute the switch, but do so two stages early. Thus,
lin-29 controls a diverse set of cellular differentiation processes, including cell cycle exit, cell fusion, stage-specific changes in cuticle gene expression and morphogenesis. In order to understand how
lin-29 regulates these aspects of terminal differentiation of seam cells, and how
lin-29 activity is temporally regulated, we have embarked on a molecular analysis of
lin-29. Genomic probes from the
lin-29 locus (Papp et. al., Nucl. Acids Res. 19:623) enabled us to isolated
lin-29 cDNAs. The transcribed region spans ~20 kb of genomic DNA. The deduced amino acid sequence of the cDNA predicts a protein containing five zinc fingers of the (Cys)2-(His)2 class, suggesting it acts as a transcription factor. Consistent with this role, we have demonstrated that a
lin-29-glutathione-S- transferase fusion protein binds DNA in vitro, and we are pursuing the specificity and relevance of such binding. Although genetic analysis predicts that
lin-29 may be activated at the fourth molt, northem analysis reveals the presence of
lin-29 transcripts (1.8 and 2.5 kb), throughout larval development, suggesting that
lin-29 may be regulated post-transcriptionally. We have begun analysis of these
lin-29 transcripts in animals mutant for the heterochronic genes, and are currently generating antibodies to
lin-29 to determine its temporal and spatial distributions.