THE HETEROCHRONIC GENE LIN-29 ENCODES A ZINC-FINGER PROTEIN THAT CONTROLS A TERMINAL DIFFERENTIATION EVENT IN CAENORHABDITIS-ELEGANS

A hierarchy of heterochronic genes, lin-4, lin-14, lin-28 and lin-29, temporally restricts terminal differentiation of Caenorhabitis elegans hypodermal seam cells to the final molt. This terminal differentiatio n event involves cell cycle exit, cell fusion and the differential reg ulation of genes expressed in the larval versus adult hypodermis, lin- 29 is the most downstream gene in the developmental timing pathway and thus it is the most direct known regulator of these diverse processes , We show that lin-29 encodes a protein with five zinc fingers of the (Cys)(2)-(HiS)(2) class and thus likely controls these processes by re gulating transcription in a stage-specific manner, Consistent with thi s role, a lin-29 fusion protein binds in vitro to the 5' regulatory se quences necessary in vivo for expression of col-19, a collagen gene ex pressed in the adult hypodermis. lin-29 mRNA is detected in the first larval stage and increases in abundance through subsequent larval stag es until the final molt, w hen lin-29 activity is required for termina l differentiation.