The Conserved Intron Binding Protein EMB-4 Plays Differential Roles in Germline Small RNA Pathways of C. elegans

Proper regulation of the germline transcriptome is essential for the maintenance of fertility and survival of a species. In C. elegans, germline transcriptome homeostasis hinges on a complex repertoire of small RNA pathways that act in both activating and silencing capacities. Our understanding of how fundamental RNA processing steps intersect with these small RNA machineries in the germline remains relatively limited. Here, we link the conserved intron binding protein and splicing factor, EMB-4/AQR/IBP160 to two key 22G-RNA pathways in the C. elegans germline. EMB-4 associates with the Argonautes CSR-1 and HRDE-1, and is enriched at the genomic loci of CSR-1 and HRDE-1 target genes. Loss of emb-4 leads to distinct alterations in CSR-1 vs. HRDE-1 small RNA and mRNA transcriptomes. Our transcriptome-wide analysis shows that EMB-4 is enriched along pre-mRNAs of nearly 10,000 transcripts. For a subset of these genes, including mostly CSR-1 pathway targets, EMB-4 enriches for intronic, but not exonic, sequences. Together these data point to EMB-4 as a factor that may help to distinguish the targets of these two germline small RNA pathways. Overall design: For mRNA and small RNA-seq experiments, total RNA was extracted from N2 and emb-4(hc60) mutant worms harvested as young adults. EMB-4 IPs were performed on RNA extracted from gravid adult N2 worms.