Transcription and multiple processing steps are required to produce specific 22 nucleotide microRNAs (miRNAs) that can regulate the expression of target genes. In C. elegans, mature
lin-4 miRNA accumulates at the end of the first larval stage to repress its direct targets
lin-14 and
lin-28, allowing the progression of several somatic cell types to later larval fates. In this study, we characterized the expression of endogenous
lin-4 and found that temporally regulated independent transcripts, but not constitutive
lin-4 containing RNAs derived from an overlapping gene, are processed to mature
lin-4 miRNA. Through an RNAi screen, we identified a conserved RNA binding protein gene
rbm-28 (R05H10.2), homologous to the human RBM28 and yeast Nop4p proteins, that is important for
lin-4 expression in C. elegans. We also demonstrate that
rbm-28 genetically interacts with the
lin-4 developmental timing pathway and uncover a previously unrecognized role for
lin-14 and
lin-28 in coordinating organismal growth.