The
let-7 microRNA (miRNA) regulates cellular differentiation across many animal species. Loss of
let-7 activity causes abnormal development in Caenorhabditis elegans and unchecked cellular proliferation in human cells, which contributes to tumorigenesis. These defects are due to improper expression of protein-coding genes normally under
let-7 regulation. While some direct targets of
let-7 have been identified, the genome-wide effect of
let-7 insufficiency in a developing animal has not been fully investigated. Here we report the results of molecular and genetic assays aimed at determining the global network of genes regulated by
let-7 in C. elegans. By screening for mis-regulated genes that also contribute to
let-7 mutant phenotypes, we derived a list of physiologically relevant potential targets of
let-7 regulation. Twenty new suppressors of the rupturing vulva or extra seam cell division phenotypes characteristic of
let-7 mutants emerged. Three of these genes,
opt-2,
prmt-1, and T27D12.1, were found to associate with Argonaute in a
let-7-dependent manner and are likely novel direct targets of this miRNA. Overall, a complex network of genes with various activities is subject to
let-7 regulation to coordinate developmental timing across tissues during worm development.