| Aspect | Key findings | Evidence type | Primary source(s) |
|---|---|---|---|
| Definition / concept | • **MEG-1** is the *Caenorhabditis elegans* protein encoded by **meg-1 / K02B9.1** (UniProt Q21126), originally defined as a **maternal-effect germ cell defective** factor required for germline development.<br>• It is an **embryo-specific germ plasm / P-granule-associated protein** and is partially redundant with **MEG-2**.<br>• Current model places MEG-1/2 not as core P-granule scaffolds, but as organizers of a distinct **germline P-body** condensate needed for germ cell fate specification. (pqac-00000001, pqac-00000003, pqac-00000006, pqac-00000008) | Genetics; immunostaining; review synthesis | Leacock & Reinke 2008, **Genetics**, doi:10.1534/genetics.107.080218, https://doi.org/10.1534/genetics.107.080218; Cassani & Seydoux 2022, **Development**, doi:10.1242/dev.200920, https://doi.org/10.1242/dev.200920; Chiappetta et al. 2022, **Biochem J**, doi:10.1042/BCJ20210815, https://doi.org/10.1042/bcj20210815 |
| Localization | • MEG-1 localizes to **embryonic P granules** from the **2-cell stage through ~100-cell stage**.<br>• In the early embryo, MEG-1 is in a **cytoplasmic gradient and small granules** in P0; in **P1-P3** it becomes enriched in puncta at the **periphery of P granules**; in **P4** it becomes distributed throughout **perinuclear P granules**; in **Z2/Z3** it disperses to the cytoplasm and is turned over by **mid-embryogenesis**.<br>• MEG-1 localization to P granules requires **MES-1**. (pqac-00000001, pqac-00000006, pqac-00000010) | Immunofluorescence imaging; developmental staging | Leacock & Reinke 2008, **Genetics**, doi:10.1534/genetics.107.080218, https://doi.org/10.1534/genetics.107.080218; Cassani & Seydoux 2022, **Development**, doi:10.1242/dev.200920, https://doi.org/10.1242/dev.200920 |
| Molecular interactions / complexes | • MEG-1 and **MEG-2** colocalize and function partially redundantly.<br>• MEG-1::GFP immunoprecipitation identified **54 enriched proteins** (>=2-fold), including canonical **P-body / mRNA-decay factors** such as **DCAP-2/DCP2, EDC-4**, CCR4-NOT-related subunits (**NTL-1, TAG-153, NTL-3**), **IFET-1**, and regulators **GLD-1, GLD-2, GLD-3, MEX-1, OMA-1, POS-1, MEX-3, SPN-4**.<br>• **POS-1** was among the most highly enriched interactors, supporting a role in post-transcriptional control.<br>• Review synthesis: MEG-1/2 nucleate a **germline P-body** distinct from, but often adjacent to, P granules, enriched for **decapping and deadenylation enzymes**. (pqac-00000006, pqac-00000008) | Proteomics / IP-MS; condensate biology review | Cassani & Seydoux 2022, **Development**, doi:10.1242/dev.200920, https://doi.org/10.1242/dev.200920; Chiappetta et al. 2022, **Biochem J**, doi:10.1042/BCJ20210815, https://doi.org/10.1042/bcj20210815 |
| Mutant / RNAi phenotypes | • **meg-1** mutants show **maternal-effect sterility**, underdeveloped adult germlines, few abnormal germ cells, and failed meiotic progression / gametogenesis.<br>• Sterility is temperature sensitive; **meg-2 RNAi** strongly enhances **meg-1** sterility: **meg-1(vr10)** rises from **15% to 100%** sterile and **meg-1(vr11)** from **4% to 93%** sterile at **20°C**.<br>• Z2/Z3 primordial germ cells are present at hatching, but later larval germ-cell proliferation fails; blocking apoptosis (**ced-4**) does not rescue the loss, arguing against canonical apoptosis as the main cause.<br>• **nos-3** loss suppresses meg-1 sterility, whereas **nos-2** loss enhances it and can abolish proliferation / promote early degeneration.<br>• **glh-1** enhances meg-1 sterility, while **pgl-1** loss partially suppresses meg-1 defects.<br>• A full **meg-1 meg-2(ax4532)** deletion causes **100% maternal-effect sterility**. (pqac-00000002, pqac-00000003, pqac-00000006, pqac-00000010) | Forward genetics; RNAi; epistasis / genetic interaction tests; cell counts | Leacock & Reinke 2008, **Genetics**, doi:10.1534/genetics.107.080218, https://doi.org/10.1534/genetics.107.080218; Kapelle & Reinke 2011, **genesis**, doi:10.1002/dvg.20726, https://doi.org/10.1002/dvg.20726; Cassani & Seydoux 2022, **Development**, doi:10.1242/dev.200920, https://doi.org/10.1242/dev.200920 |
| Pathway / regulatory model | • Early work linked MEG-1 to **P-granule segregation and embryonic germline integrity**; later work refined this to a role in **post-transcriptional regulation** rather than simply granule inheritance.<br>• Wang et al. showed MEG proteins are **serine-rich intrinsically disordered proteins** whose phosphorylation state regulates granule dynamics; **meg-1** contributes to **P-granule disassembly** in the early embryo and acts genetically downstream of **MBK-2** and **PPTR-1/2** pathways controlling condensation/disassembly.<br>• Cassani & Seydoux proposed that MEG-1/2 stabilize **germline P-bodies** in **P4**, enabling turnover of maternal oogenic transcripts and proper translation of germline determinants such as **NOS-2**; this is required to specify **P4 as the germline founder cell**.<br>• Thus, current understanding is that MEG-1 acts in a **germ-plasm mRNA regulation pathway** coupling condensate specialization to **maternal mRNA decay / translational control**. (pqac-00000005, pqac-00000006, pqac-00000007, pqac-00000008) | Genetics; live imaging; phosphorylation / signaling analysis; RNA regulation studies; review synthesis | Wang et al. 2014, **eLife**, doi:10.7554/eLife.04591, https://doi.org/10.7554/eLife.04591; Cassani & Seydoux 2022, **Development**, doi:10.1242/dev.200920, https://doi.org/10.1242/dev.200920; Chiappetta et al. 2022, **Biochem J**, doi:10.1042/BCJ20210815, https://doi.org/10.1042/bcj20210815 |
| Quantitative / statistics | • **Sterility enhancement** at 20°C with meg-2 RNAi: **meg-1(vr10) 15% -> 100%**, **meg-1(vr11) 4% -> 93%** sterile. (pqac-00000003, pqac-00000010)<br>• **meg-1 meg-2(ax4532)**: **100% maternal-effect sterile**. (pqac-00000006)<br>• RNA-seq in **meg-1 meg-2** embryos: **230 downregulated** and **550 upregulated** genes. (pqac-00000007)<br>• Of the upregulated genes, **223** overlapped with genes whose poly(A) tails are extended in **pos-1(RNAi)** embryos (**P = 0.0002**). (pqac-00000007)<br>• Germline fate transformation markers in meg-1 meg-2: **hlh-1 ectopic in 21/23 embryos vs 0/21 WT**; **xnd-1 absent/weak in 16/24 embryos**. (pqac-00000007)<br>• Extra P granule-positive cells: **50%** of bean-to-comma embryos and **100%** of non-fed L1 larvae. (pqac-00000007)<br>• Severe combinatorial meg mutant phenotypes: **meg-1;meg-3;meg-4** larvae had **<10 germ cells** and were **100% sterile**; earlier cited work also notes **meg-1;meg-2** double mutants as **100% sterile**. (pqac-00000005) | Quantitative genetics; RNA-seq; marker scoring; larval germ-cell counts | Leacock & Reinke 2008, **Genetics**, doi:10.1534/genetics.107.080218, https://doi.org/10.1534/genetics.107.080218; Wang et al. 2014, **eLife**, doi:10.7554/eLife.04591, https://doi.org/10.7554/eLife.04591; Cassani & Seydoux 2022, **Development**, doi:10.1242/dev.200920, https://doi.org/10.1242/dev.200920 |


*Table: This table summarizes experimentally supported functional annotation for C. elegans MEG-1, including localization, molecular partners, mutant phenotypes, regulatory model, and quantitative findings from key primary studies and one authoritative review.*