Cells of a developing animal must interpret at least three different types of informational cues: position, sex, and developmental time. Mutations in the heterochronic genes of C. elegans alter the timing of many stage-specific developmental events, including the terminal differentiation of the lateral hypodermal seam cells during the final (L4) molt. lin-4, lin-14(gf), and lin-29 mutant animals undergo retarded development; seam cells fail to terminally differentiate and instead reiterate cell division patterns normally associated with an earlier stage. Conversely, lin-14(lf) and lin-28 mutant animals develop precociously; seam cells express cell division patterns normally reserved for a later stage in the same lineage. Epistasis analysis has ordered these genes into a regulatory hierarchy (Ambros, 1989) . The collective action of the early acting genes, lin-4, lin-14, and lin-28 ensures the correct temporal execution of seam cell terminal differentiation by regulating the time of lin-29 activity. Determining how the heterochronic genes specify temporal information requires identifying all members of the pathway and understanding their functions. To this end, our lab has cloned lin-42, another gene that appears to control the proper timing of seam cell terminal differentiation. Seam cells in lin-42 mutant animals terminally differentiate precociously during the L3 molt. The putative lin-42 protein contains a PAS domain known to mediate protein-protein interactions in other proteins (Huang et al., 1993) . The LIN-42 PAS domain is most similar to the PAS domains found in the Period class of insect circadian rhythm proteins. The PAS domain is the first identified motif shared between members of these two types of developmental timing pathways. We wish to test if this conservation of sequence reflects a conservation of function between these proteins. A hallmark of circadian rhythm genes is the cycling of their mRNA and protein products with a circadian periodicity. Therefore, we are characterizing the temporal expression patterns of lin-42. We are performing western blot analysis and RT-PCR to generate a developmental profile of lin-42 protein and mRNA, respectively. These techniques and reagents will then be used to test for oscillation of lin-42 expression patterns similar to the known cyclical nature of circadian rhythm gene products. Ambros, V. (1989) Cell 57, 49-57. Huang, Z. J., Edery, I., & Rosbash, M. (1993) Nature 364, 259-262.

Affiliation:
- Department of Genetics and Cell Biology, University of Minnesota, St. Paul, MN 55108 Department of Biochemistry, University of Minnesota, St. Paul, MN 55108 Department of Genetics and Cell Biology, Department of Biochemistry, University of Minnesota, St. Paul, MN 55108