Imp, a key regulator of transposable elements, cell growth, and differentiation genes during embryogenesis
Imps are a highly conserved family of RNA-binding proteins involved in embryonic development, cancer progression, and neurogenesis. However, the molecular pathways and RNAs regulated by Imp to control these processes remain poorly understood. Embryos derived from Imp mutant germline clones arrest development, and transcriptome analysis revealed significant dysregulation of genes involved in cell growth, differentiation, tube morphogenesis, neuronal projection development, and RNA metabolism, along with de-repression of transposable element (TE) RNAs. Consistent with these findings, Imp mutant embryos display TE-overexpression phenotypes, are smaller in size, and exhibit defective organ development, including impaired tracheal branching and gastrulation. Reduced levels of Imp at the larval neuromuscular junction (NMJ) impair synaptic bouton formation and decrease adult longevity. RIP-seq experiments showed that Imp-associated RNAs are enriched for TE RNAs. Proteomic analyses confirmed that several TE-encoded proteins are upregulated in Imp mutant embryos. Specifically, the Ty1 family retrotransposon Copia was derepressed. Consistent with recent findings that Copia is a potent inhibitor of synaptogenesis, its upregulation likely contributes to the impaired NMJ formation and broader embryonic defects observed in Imp mutants. Moreover, Imp associates with piRNA pathway proteins, ensures Piwi nuclear localization, and--like piwi mutants--its loss disrupts TE silencing and causes position-effect variegation (PEV) defects. The analysis of Imp complexes further points to potential mechanisms by which Imp may regulate TE expression. Overall, these results indicate that Imp maintains genome stability and ensures proper developmental progression and neuronal activity by regulating post-transcriptional processes and suppressing transposons.