MEG-3 (as GEI-12) was identified as a GEX-3 interacting protein via yeast two-hybrid screening

MEG-1 and MEG-3 are substrates of kinase MBK-2/DYRK and phosphatase PP2A(PPTR-1/2)

Phosphorylation of MEGs promotes granule disassembly; dephosphorylation promotes assembly

GFP-tagged MEG-3 localizes to a dynamic domain that surrounds and penetrates each P granule

MEG proteins are required redundantly for fertility

P granules are non-homogeneous structures whose assembly is regulated by phosphorylation

P granule asymmetry in the polarized zygote depends on RNA-induced phase separation of the granule scaffold MEG-3; MEG-3 binds and phase separates with RNA in vitro.

MEG-3 forms a posterior-rich gradient anti-correlated with MEX-5, which is necessary and sufficient to suppress MEG-3 granule formation by interfering with MEG-3's access to RNA.

P granules recruit mRNAs by condensation with MEG-3, which traps mRNAs into non-dynamic condensates in vitro and binds ~500 mRNAs in vivo in a sequence-independent manner favoring embryonic mRNAs with low ribosome coverage.

Localization to P granules is required to enrich mRNAs in the germ lineage for robust germline development; intrinsically-disordered proteins drive RNA condensation during P granule assembly.

MEG-3 is a modular protein that uses its N-terminal IDR to bind RNA and its C-terminus to drive condensation; the HMGL motif mediates binding to PGL-3 and is required for co-assembly of MEG-3 and PGL-3 condensates in vivo.

P granule assembly requires MEG-3, an intrinsically disordered protein that forms RNA-rich condensates on the surface of PGL condensates at the core of P granules.

MEG-3's primary biochemical role is as an RNA-condensate scaffold: an intrinsically disordered protein that binds RNA broadly and uses RNA-stimulated condensation to spatially organize germ-plasm RNP (P-granule) condensates, rather than acting as an enzyme or transporter.

MEG-3 is maternally supplied and forms an anterior-low/posterior-high cytoplasmic gradient, occupying a peri-granular domain that surrounds and penetrates P granules.

Posterior P-granule asymmetry in the polarized zygote depends on RNA-induced phase separation/condensation of MEG-3, which acts upstream of stable PGL/GLH granule retention.

MEG-3 is modular: an N-terminal intrinsically disordered region (IDR) binds RNA, and a C-terminal predicted ordered HMG-like motif (HMGL) contributes to condensation and mediates binding to PGL-3 for co-assembly of the composite granule.

MEG-3 binds approximately 500 mRNAs in vivo (iCLIP), with bound transcripts enriched for long embryonic mRNAs with low ribosome occupancy, consistent with broad, largely sequence-independent RNA binding rather than catalytic specificity.

MEG-3 is an experimentally identified substrate of the DYRK-family kinase MBK-2 and is regulated by PP2A phosphatase activity (PPTR-1/2-associated); MBK-2 phosphorylation promotes granule disassembly whereas PP2A/PPTR antagonizes MBK-2 and promotes assembly.

MEX-5, an anterior-enriched RNA-binding protein, acts as an mRNA sink that suppresses MEG-3 condensation in the anterior cytoplasm, spatially patterning MEG-3 condensation via gradients in RNA availability.

MEG-3 recruits maternal mRNAs into granules by forming a gel-like RNA-rich phase on the surface of more dynamic PGL condensates.

MEG-3/4 act upstream of PGL components in zygotes, being needed for stable, asymmetric posterior P-granule assembly and for segregation of granule contents into germline blastomeres; the germ-plasm/fertility roles are downstream of this scaffold activity.

Loss of MEG proteins causes fertility defects that worsen in combination: meg-3 meg-4 mutants show ~30% sterility and the meg-1 meg-3 meg-4 triple mutant is 100% sterile, indicating overlapping but essential germ-plasm functions.