The TRIM family protein, NHL-2, functions as a micro-RNA RISC co-factor in somatic tissues.
nhl-2 null mutants display multiple germline defects, including oocyte chromosomal defects, reduced brood size and embryonic lethality. To investigate the function of NHL-2, we conducted a genome-wide RNAi screen to identify genes that lead to synthetic phenotypes when knocked down in
nhl-2 null mutants. Our screen identified 40 candidate genes, including the DEAD box RNA helicase,
drh-3, which is required for the biogenesis of CSR-1 and WAGO-1 22G small RNAs. Knockdown of
drh-3 in
nhl-2 null mutants leads to marked chromosomal abnormalities in diakinetic oocytes and anaphase embryos, as well as significantly enhanced embryonic lethality. Similar phenotypes were observed when
csr-1 and other 22G RNA pathway co-factors were knocked down in
nhl-2 null mutants, including
cde-1 and
ekl-1, suggesting that NHL-2 influences CSR-1 22G RNA activity. In addition to this, qRT-PCR data shows that NHL-2 contributes to the downregulation of selected WAGO-1 22G RNA targets, including protein coding genes, transposons and pseudogenes. Moreover, we show that NHL-2 is required for accurate histone modifications, centromere formation and positively regulates histone gene expression. Taken together, our results suggest that NHL-2 contributes to genome maintenance and germline chromosomal integrity by influencing WAGO-1 and CSR-1 22G RNA pathways.