ELLI-1, a novel germline protein, modulates RNAi activity and P-granule accumulation in Caenorhabditis elegans

Abstract

Germ cells contain non-membrane bound cytoplasmic organelles that help maintain germline integrity. In C. elegans they are called P granules; without them, the germline undergoes partial masculinization and aberrant differentiation. One key P-granule component is the Argonaute CSR-1, a small-RNA binding protein that antagonizes accumulation of sperm-specific transcripts in developing oocytes and fine-tunes expression of proteins critical to early embryogenesis. Loss of CSR-1 complex components results in a very specific, enlarged P-granule phenotype. In a forward screen to identify mutants with abnormal P granules, ten alleles were recovered with a csr-1 P-granule phenotype, eight of which contain mutations in known components of the CSR-1 complex (csr-1, ego-1, ekl-1, and drh-3). The remaining two alleles are in a novel gene now called elli-1 (enlarged germline granules). ELLI-1 is first expressed in primordial germ cells during mid-embryogenesis, and continues to be expressed in the adult germline. While ELLI-1 forms cytoplasmic aggregates, they occasionally dock, but do not co-localize with P granules. Instead, the majority of ELLI-1 aggregates accumulate in the shared germline cytoplasm. In elli-1 mutants, several genes that promote RNAi and P-granule accumulation are upregulated, and embryonic lethality, sterility, and RNAi resistance in a hypomorphic drh-3 allele is enhanced, suggesting that ELLI-1 functions with CSR-1 to modulate RNAi activity, P-granule accumulation, and post-transcriptional expression in the germline.

PQN-75 is expressed in the pharyngeal gland cells of C aenorhabditis elegans and is dispensable for germline development

“…A mutagenesis screen for effectors of P-granule assembly and distribution isolated multiple alleles of a gene encoding the Argonaute protein CSR-1 ( Andralojc et al, 2017 ). Whole genome sequencing revealed that one of these alleles, csr-1(sam18) , also contained a linked Gly to Asp mutation in pqn-75 ( Fig.…”

DAF-18/PTEN inhibits germline zygotic gene activation during primordial germ cell quiescence

“…To determine whether the inappropriate zygotic germline expression seen in starved daf-18 mutant PGCs was specific to VBH-1, we investigated another germline gene reporter: GLH-1::GFP (Germ Line Helicase), a component of germline-specific P granules (Gruidl et al 1996). We used an available GLH-1::GFP CRISPR allele (Andralojc et al 2017), and crossed it in from the male to examine zygotic protein expression. Like GFP::VBH-1, we found that in PGCs of starved daf-18 mutant animals, the level of zygotic GLH-1::GFP expression was significantly elevated compared to the wild type within a few hours of hatching ( Figure 4C).…”

Germline maintenance through the multifaceted activities of GLH/Vasa inCaenorhabditis elegansP granules

“…All scale bars are 20 microns. For immunostained images ( Figure 4A/B/C), worms and embryos were fixed and stained with anti-GFP monoclonal and anti-PGL-1 polyclonal antibodies as previously described (Andralojc et al, 2017).…”