MEG-2 (Maternal Effect Germ cell defective 2) is a highly intrinsically disordered protein (87% disordered residues) that localizes to P granules during C. elegans embryogenesis. It functions redundantly with MEG-1 to regulate P granule dynamics through phase separation mechanisms. MEG-2 has an acidic predicted pI of 6.04 and a serine-rich N-terminus characteristic of MEG proteins. Phosphorylation of MEG-1/2 by kinase MBK-2 promotes P granule disassembly in the anterior cytoplasm, while dephosphorylation by PP2A promotes P granule assembly in the posterior. This asymmetric regulation ensures proper segregation of P granules to the germline during early embryonic divisions. Loss of meg-2 in combination with meg-1 causes sterility and P granule mis-segregation to somatic blastomeres. A refined model (Cassani & Seydoux 2022, PMID:36196602) reassigns MEG-1/2 to a distinct germ-plasm condensate, the germline P-body, which is separable from canonical (PGL/MEG-3/4) P granules and enriches mRNA decapping/deadenylation regulators (CGH-1/DDX6, EDC-3) and the RNA-binding protein POS-1. In the germline founder cell P4, MEG-1/2 maintain these P-body factors and robust mRNA deadenylation; meg-1 meg-2 embryos mis-specify P4, ectopically express somatic programs, and fail to develop a germline, indicating MEG-2 function extends beyond P granule physical dynamics to maternal mRNA regulation and germ cell fate specification. MEG-2 itself has no known catalytic, sequence-specific binding, or transporter activity and acts as a non-enzymatic condensate scaffold/organizer.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005515 protein binding | IPI PMID:14704431 A map of the interactome network of the metazoan C. elegans. | REMOVE | Summary: High-throughput yeast two-hybrid screen identified interaction between MEG-2 and EYA-1 (O17670). The publication describes a large-scale interactome mapping effort detecting over 4000 interactions. While the interaction may be real, the generic 'protein binding' term provides no functional insight. No specific functional context for this interaction is established in the literature. Reason: The 'protein binding' term is uninformative as a GO annotation per curation guidelines. High-throughput Y2H interactions without validation or functional characterization should not be annotated with this generic term. The MEG-2/EYA-1 interaction has no established biological significance in germline development or P granule function. Falcon deep research independently found no functional role for MEG-2 as a sequence-specific binding protein, concluding that MEG-2 is a non-enzymatic intrinsically disordered scaffold with no assigned catalytic reaction, substrate, or transporter activity. Supporting Evidence: PMID:14704431 more than 4000 interactions were identified from high-throughput, yeast two-hybrid (HT=Y2H) screens file:worm/meg-2/meg-2-deep-research-falcon.md MEG-2 is not assigned a catalytic reaction, substrate specificity, or transporter substrate |
| GO:0005515 protein binding | IPI PMID:19123269 Empirically controlled mapping of the Caenorhabditis elegans... | REMOVE | Summary: This is from a second high-throughput yeast two-hybrid mapping effort (Worm Interactome 2007). The publication describes quality-controlled protein-protein interaction mapping detecting the same MEG-2/EYA-1 interaction. While the interaction was detected in two independent screens, no functional context is established. Reason: Same rationale as the previous annotation - 'protein binding' is uninformative and does not capture any specific molecular function. The duplicate annotation from a related interactome study adds no additional functional information. If a more specific binding function were established (e.g., specific role in P granule assembly), a more informative MF term should be used. Supporting Evidence: PMID:19123269 We present an expanded C. elegans protein-protein interaction network, or 'interactome' map, derived from testing a matrix of approximately 10,000 x approximately 10,000 proteins |
| GO:1903864 P granule disassembly | IGI PMID:25535836 Regulation of RNA granule dynamics by phosphorylation of ser... | ACCEPT | Summary: Well-supported annotation based on genetic interaction evidence. Wang et al. (2014) demonstrated that MEG-1 and MEG-2 are required for P granule dynamics in embryos. The publication shows that phosphorylation of MEG proteins by MBK-2/DYRK kinase promotes granule disassembly in the anterior cytoplasm (PMID:25535836). Reason: This annotation accurately captures a core molecular function of MEG-2. The IGI evidence from PMID:25535836 demonstrates that simultaneous loss of meg-1 and meg-2 causes defects in P granule disassembly, with P granules failing to disassemble properly in the anterior cytoplasm of the P1 blastomere. Falcon deep research supports the disassembly role via MEG-2's acidic predicted pI (6.04), which biases the MEG-1/2 pair toward granule dissolution in contrast to the basic MEG-3/4 pair that favors assembly. Supporting Evidence: PMID:25535836 Phosphorylation of the MEGs promotes granule disassembly and dephosphorylation promotes granule assembly file:worm/meg-2/meg-2-deep-research-falcon.md predicted unphosphorylated pI **MEG-2 = 6.04** (acidic), compared with MEG-3/4 basic pIs. This supports a hypothesis that MEG-1/2 (including MEG-2) bias toward disassembly roles, while MEG-3/4 provide stronger assembly contributions. |
| GO:0043186 P granule | IDA PMID:18202375 MEG-1 and MEG-2 are embryo-specific P-granule components req... | ACCEPT | Summary: Cellular component annotation demonstrating MEG-2 localization to P granules during embryogenesis. Leacock and Reinke (2008) showed that MEG-1 and MEG-2 are embryo-specific P granule components that localize to P granules from the 4-8 cell stage through subsequent P cell divisions (PMID:18202375). Reason: This is a core cellular localization for MEG-2. The IDA evidence from direct observation of MEG-2 localization to P granules in embryos is well-established. MEG-2 is one of the defining embryo-specific components of P granules. Falcon deep research confirms GFP::MEG-2 localizes to embryonic P granules in the P lineage (P2/P3/P4) and primordial germ cells Z2/Z3. Note that a more refined view (Cassani & Seydoux 2022, PMID:36196602) reassigns MEG-2 to a distinct germline-P-body condensate that is physically separable from canonical (PGL/MEG-3/4) P granules; however, no specific 'germline P-body' GO term yet exists, so the broader P granule (GO:0043186) component term remains the best available representation of MEG-2 localization. Supporting Evidence: PMID:18202375 encode proteins that localize exclusively to P granules during embryonic germline segregation file:worm/meg-2/meg-2-deep-research-falcon.md GFP::MEG-2 localizes to **P granules** in the embryonic P lineage (P2/P3/P4) and the primordial germ cells **Z2/Z3** (embryonic stages). PMID:36196602 In this study, we describe a second condensate type, germline P-bodies, that contains regulators of mRNA adenylation and decapping, the RNA-binding protein POS-1, and MEG-1 and MEG-2, two intrinsically-disordered proteins related to MEG-3 and MEG-4. |
| GO:1903863 P granule assembly | IGI PMID:25535836 Regulation of RNA granule dynamics by phosphorylation of ser... | NEW | Summary: Proposed new annotation based on evidence from Wang et al. (2014) showing that dephosphorylated MEG-1/MEG-2 promotes P granule assembly in the posterior cytoplasm. The literature establishes a dual role for MEG proteins in both assembly and disassembly depending on phosphorylation state. Reason: The existing annotations only capture the disassembly function, but MEG-2 also has a documented role in promoting P granule assembly when dephosphorylated. UniProt annotation states: "Together with dephosphorylated meg-1, promotes the assembly and accumulation of zygotic P granules in the posterior cytoplasm of pre-gastrulation embryos." Supporting Evidence: PMID:25535836 Phosphorylation of the MEGs promotes granule disassembly and dephosphorylation promotes granule assembly |
| GO:0140693 molecular condensate scaffold activity | IGI PMID:25535836 Regulation of RNA granule dynamics by phosphorylation of ser... | NEW | Summary: MEG-2 functions as a scaffold protein for P granule condensates through its intrinsically disordered regions. The MEG proteins regulate liquid-like P granule dynamics through phase separation mechanisms. Reason: MEG-2 is an intrinsically disordered protein that regulates P granule condensate dynamics. P granules behave as liquid droplets whose dynamics depend on MEG proteins. This molecular function term captures the scaffold role of MEG-2 in condensate formation. Falcon deep research independently synthesizes the literature to describe MEG-2 as a non-enzymatic, low-complexity/IDP-like condensate organizer/scaffold, consistent with this molecular function term. Evidence type is IGI (not IDA): no direct biochemical/biophysical assay of MEG-2 scaffold activity was performed; the scaffold role is inferred from the genetic interaction of meg-1 meg-2 in controlling P granule dynamics (PMID:25535836, which directly demonstrated phosphorylation of MEG-1/MEG-3, not MEG-2) together with MEG-2's IDP/low-complexity properties, matching the IGI evidence used for the other meg-1/meg-2 annotations from this same paper. Supporting Evidence: PMID:25535836 RNA granules have been likened to liquid droplets whose dynamics depend on the controlled dissolution and condensation of internal components file:worm/meg-2/meg-2-deep-research-falcon.md it is instead described as an **intrinsically disordered/low-complexity protein** that likely serves as a **condensate organizer/scaffold** in post-transcriptional regulation |
| GO:0007281 germ cell development | IMP PMID:36196602 Specialized germline P-bodies are required to specify germ c... | NEW | Summary: Beyond regulating P granule physical dynamics, MEG-2 (redundantly with MEG-1) is required for the germline founder cell P4 to adopt and maintain germ cell fate. Cassani & Seydoux (2022) showed that embryos lacking meg-1 and meg-2 mis-specify the germline founder cell, fail to robustly activate germline transcriptional programs, and do not develop a germline, leading to fully penetrant sterility. This developmental endpoint of MEG-2 function is captured by germ cell development (GO:0007281). Reason: The existing annotations capture MEG-2's P granule organization and condensate scaffold roles but not the downstream developmental outcome. The Cassani & Seydoux (2022) genetic loss-of-function study (PMID:36196602) demonstrates, via mutant-phenotype (IMP) evidence, that meg-1 meg-2 loss mis-specifies the germline founder cell P4 and abolishes germline development, supporting germ cell development as a biological process MEG-2 is directly involved in. Falcon deep research highlights this 2022 study as the strongest modern functional source for the MEG-1/2 pair. Supporting Evidence: PMID:36196602 Our findings indicate that, unlike P granules, ‘germline P-bodies’ are essential for maternal mRNA regulation and specification of P4 as the germline founder cell. file:worm/meg-2/meg-2-deep-research-falcon.md embryos lacking meg-1/2 mis-specify the germline founder cell and fail to develop a germline, resulting in **100% sterility** in the reported meg-1 meg-2 loss paradigms |
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