Genetic studies have shown that heterochronic genes govern the timing of development in C. elegans . The 21 nucleotide RNA,
let-7 , is predicted to bind to complementary sites in the 3'UTR of its target gene,
lin-41 , causing the down-regulation of
lin-41 at the L/A (larva-to-adult) switch. Together these two heterochronic genes act to regulate the timing of proliferation vs. differentiation in seam cells at the L/A switch through an unknown mechanism. Gene regulation by 3'UTRs is used by all eukaryotic cells, but little is known about the mechanism. Similarly, while there is presently substantial interest in gene regulation by small RNA molecules (e.g. RNAi), very little is known about their mechanism of action. A genetic screen for
let-7 -like mutants was performed in order to find genes that may function with
let-7 . Two recessive mutations recovered in the screen,
mg281 and
mg283, define a new gene
lin-63 that most likely acts with
let-7 to regulate
lin-41 . Similar to
let-7 mutants, seam cells fail to terminally differentiate correctly in
lin-63 mutant adults. Moreover, like in
let-7 mutants, a reporter gene bearing the
lin-41 3'UTR fails to be turned off in adult staged
lin-63 mutants.
lin-63 maps near
lin-29 but complements
lin-29 . Purified
let-7 RNA binds to and gel shifts RNA from
lin-41 3'UTR, but not RNA deleted for the
let-7 complementary sites. To identify potential proteins that recognize the
let-7 /
lin-41 duplex we performed a yeast 3 hybrid screen with the
let-7 /
lin-41 RNA duplex as bait. One interactor maps close to where
lin-63 maps, making it a good candidate for
lin-63 . We are testing whether our
lin-63 alleles are in this gene. Molecular identification of
lin-63 is underway and should help determine the mechanism by which these small RNA molecules act to down-regulate their target molecules.