The precise temporal control of gene expression is an essential aspect of metazoan development. After embryogenesis, the ecdysozoan nematode C. elegans goes through four larval stages (L1 - L4), molting its outer cuticle covering between each, before becoming an adult. The cuticle in each stage is unique, and the major components of the cuticle are nematode-specific cuticle collagen proteins, which are expressed from a large gene family in this species. Examination of modENCODE project RNAseq temporal developmental data showed that during C. elegans development a majority of cuticle collagen (col) genes (116/187) display a strong peak of expression in only one developmental stage. This set of temporally co-regulated similar genes provides a powerful system to study temporal regulation of gene expression. Our work is focused on a subset of col genes that peak during the L4 larval stage: bli-1, col-38, col-49, col-63, col-138 and col-175. Transcriptional YFP reporters for these genes showed peaks of expression in the hypodermis during the L4 stage. Deletion analyses narrowed the necessary promoter regions to fragments of 262, 222 and 282 bp in col-38, col-63 and col-49, respectively. In C. elegans, developmental timing is controlled by the heterochronic pathway of proteins and miRNAs. The most downstream effector of this pathway is LIN-29, a zinc finger transcription factor required for the larval-to-adult ‘switch’ in hypodermal cells. As lin-29 was previously shown to regulate expression of an adult cuticle col gene, we investigated the role of lin-29 in expression of our L4-specific col genes. We examined the effects of both lin-29 loss- and gain-of-function on L4 col YFP transcriptional reporters as well as on endogenous col gene transcription levels, and found that LIN-29 is required for robust expression of col genes in the L4 stage, and sufficient for misexpression of L4-col genes at other developmental times. We also found that LIN-29 protein binds in gel shift assays to the smallest col gene promoter fragments necessary for in vivo expression. These fragments each contain several putative LIN-29 DNA binding motifs, and the requirement for these sites for in vitro binding and in vivo expression is being tested. Taken together, these results strongly suggest direct regulation of stage-specific col genes by LIN-29 during the L4 stage. In order to expand our work on the temporal regulation of gene expression during the L4, we are currently performing a genome-wide search for LIN-29 target genes using temporal misexpression of LIN-29 and RNAseq. Results will be reported.