| Process/role | Molecular mechanism | Substrate (protein) and phosphosite(s) | Evidence type | Key quantitative/phenotypic data | Primary source with year, DOI, and URL |
|---|---|---|---|---|---|
| Identity and core biochemical function in the oocyte-to-embryo transition | MBK-2 is a maternally supplied DYRK-family dual-specificity kinase whose kinase activity is essential for marking a subset of maternal proteins for timed post-meiotic turnover; activity depends on catalytic competence and DYRK-like phosphorylation of Ser/Thr substrates in consensus motifs | MEI-1 S92; OMA-1 DYRK consensus site affected by P240L mutation; not POS-1 in vitro (pqac-00000002, pqac-00000001) | In vitro kinase assays; transgenic rescue; genetics | mbk-2(pk1427) maternal embryos: 0% viability (n=1063); GFP::MBK-2 rescue: 80% viability (n=569); kinase-dead GFP::MBK-2(K196R): 0% viability (n=198) (pqac-00000002) | Stitzel et al., 2006. DOI: 10.1016/j.cub.2005.11.063. URL: https://doi.org/10.1016/j.cub.2005.11.063 |
| Timed degradation of maternal proteins after meiosis | MBK-2 functions as a temporal activator of maternal protein degradation during the egg-to-embryo transition, likely by phosphorylation that creates degradation competence after meiotic progression | PIE-1, OMA-1, MEI-1/MEI-2; phosphosites not mapped in this study (pqac-00000003, pqac-00000004) | Live imaging/genetics with GFP reporters; epistasis | GFP::PIE-1ZF1 failed to degrade in mbk-2(RNAi) embryos (n=8); OMA-1::GFP persisted in 34/34 mat-1 zygotes; GFP::MEI-1 persisted in 40/44 mat-1 zygotes (pqac-00000003, pqac-00000004) | Pellettieri et al., 2003. DOI: 10.1016/S1534-5807(03)00231-4. URL: https://doi.org/10.1016/S1534-5807(03)00231-4 |
| OMA-1 destruction and remodeling of OMA-1 function | MBK-2 directly phosphorylates OMA-1 at T239; this acts as a molecular switch promoting later degradation and enabling OMA-1 functional transition; T239 phosphorylation primes subsequent GSK-3 phosphorylation at T339 | OMA-1 T239; GSK-3-dependent downstream T339; oma-1(zu405) P240L reduces T239 phosphorylation (pqac-00000000, pqac-00000001) | In vitro kinase assay; phospho-specific antibody in vivo; phosphomimetic/nonphosphorylatable reporter genetics | T239 phosphorylation detected shortly after meiosis II; T239D enhances later T339 phosphorylation; T239A and T339A delay degradation of OMA-1::GFP; reduced T239 phosphorylation in oma-1(zu405) causes persistence past 1-cell stage and embryonic lethality (pqac-00000000, pqac-00000001) | Nishi, 2007; summarized by Robertson & Lin, 2013. DOI: 10.1007/978-1-4614-4015-4_12. URL: https://doi.org/10.1007/978-1-4614-4015-4_12 |
| OMA-1 destruction in the first embryonic cell cycle | MBK-2 is one of several conserved kinases that promote OMA-1 destruction during the oocyte-to-embryo transition; OMA-1 destruction permits downstream ZIF-1-dependent proteolysis of cell-fate determinants | OMA-1; site not specified in this source (pqac-00000006) | Mutant isolation/genetics | OMA-1 peaks in maturing oocytes and begins to disappear only after the fertilized egg enters the first mitosis; mbk-2 mutation stabilizes OMA-1, and this stabilization is partially suppressed by oma-1 loss-of-function (pqac-00000006) | Shirayama et al., 2006. DOI: 10.1016/j.cub.2005.11.070. URL: https://doi.org/10.1016/j.cub.2005.11.070 |
| MEI-1 degradation at the meiosis-to-mitosis transition | MBK-2 directly phosphorylates MEI-1 on S92, a DYRK consensus site overlapping a PEST sequence; phosphorylation precedes and is required for developmental degradation | MEI-1 S92 (pqac-00000002, pqac-00000018) | In vitro kinase assay; phospho-S92 antibody in vivo; mutant reporter genetics | GFP::MEI-1(R36C) is degraded at meiosis-to-mitosis transition, whereas GFP::MEI-1(R36C,S92A) persists past first mitosis; phosphorylation/degradation occur in unfertilized spe-9 eggs, are blocked by meiotic arrest, and accelerated by wee-1.3(RNAi) (pqac-00000002, pqac-00000018) | Stitzel et al., 2006. DOI: 10.1016/j.cub.2005.11.063. URL: https://doi.org/10.1016/j.cub.2005.11.063 |
| Katanin regulation: stability and enzymatic inhibition | MBK-2 phosphorylates the katanin complex in the N-terminal regulatory region of MEI-1; S92 is the principal site for degradation targeting, while phosphorylation of N-terminal sites suppresses MT-stimulated ATPase activity | MEI-1 S90, S92, S113, S137; MEI-2 T32, S68, S86 (MEI-2 phosphorylation requires MEI-1) (pqac-00000016, pqac-00000017, pqac-00000020) | LC-MS/MS; in vitro kinase assays; ATPase assays; MEL-26 binding assays; in vivo mutant analysis | S92G reduces 32P incorporation by ~80%; MTs normally stimulate katanin ATPase ~2–3-fold, but this stimulation is lost after MBK-2 phosphorylation; S92 phosphorylation is necessary and sufficient for MEL-26 binding/degradation targeting; nonphosphorylatable S92A accumulates to ~3-fold higher levels and causes spindle defects, whereas S92D resembles WT for accumulation (pqac-00000016, pqac-00000019, pqac-00000020) | Joly et al., 2020. DOI: 10.1083/jcb.201912037. URL: https://doi.org/10.1083/jcb.201912037 |
| Cell-cycle-linked activation and localization control | MBK-2 is restrained in oocytes by cortical anchoring with EGG-3/EGG-4/5; it autophosphorylates on a YTY motif during translation, CDK-1 phosphorylates S68, and APC/C-dependent release/degradation of EGG proteins allows active MBK-2 to access cytoplasmic substrates | MBK-2 regulatory sites: YTY autophosphorylation motif; S68 phosphorylation by CDK-1 (pqac-00000008, pqac-00000001) | Review synthesis of prior primary studies; localization and regulatory genetics summarized | Phosphorylated substrates first detectable in 1-cell embryos at anaphase of meiosis I and peak after second polar body extrusion; MBK-2 is cortical before sperm signal, then relocalizes to cytoplasmic puncta through meiosis II (pqac-00000008, pqac-00000001) | Robertson & Lin, 2013. DOI: 10.1007/978-1-4614-4015-4_12. URL: https://doi.org/10.1007/978-1-4614-4015-4_12 |
| Dynamic relocalization during meiosis | MBK-2 relocalizes in a two-step, cell-cycle-dependent manner from uniform cortex to cortical puncta and then into cytoplasm; progression through meiosis, not fertilization, is the trigger | No substrate phosphosite; localization behavior of MBK-2 itself (pqac-00000009, pqac-00000011, pqac-00000012) | GFP::MBK-2 live imaging; cell-cycle perturbation genetics | Cortical foci in 0/9 meiosis I metaphase/anaphase embryos, 3/4 telophase I/prophase II embryos, and 18/18 meiosis II metaphase/anaphase embryos; 78% of mat-1(RNAi) embryos (n=292) retained uniform cortical MBK-2; kinase-dead K196R showed aberrant spindle localization in 37/66 embryos vs 0/43 WT (pqac-00000009, pqac-00000002, pqac-00000011) | Pellettieri et al., 2003; Stitzel et al., 2006. DOI: 10.1016/S1534-5807(03)00231-4; 10.1016/j.cub.2005.11.063. URLs: https://doi.org/10.1016/S1534-5807(03)00231-4 ; https://doi.org/10.1016/j.cub.2005.11.063 |
| Early embryonic polarity and germ-plasm asymmetry | MBK-2 is required not only for degradation but also for proper posterior enrichment/segregation of PIE-1 and P granules, acting downstream of meiotic progression and independently of general microtubule failure | PIE-1 and germ-plasm regulators; phosphosite(s) not mapped here (pqac-00000004, pqac-00000007) | Genetics; live imaging/phenotypic analysis | mbk-2 mutants proceed through meiosis into mitosis but fail to localize P granules and POS-1 properly and fail to degrade maternal proteins; PIE-1::GFP asymmetry averaged 2.0 embryos per gonad in mat-1(ax227) (n=28) and mat-1(ax227); mbk-2(RNAi) (n=29) backgrounds (pqac-00000004, pqac-00000007) | Pellettieri et al., 2003. DOI: 10.1016/S1534-5807(03)00231-4. URL: https://doi.org/10.1016/S1534-5807(03)00231-4 |
| Developmental necessity and phenotype spectrum | Maternal MBK-2 is essential for meiosis-to-mitosis transition and early embryogenesis; defective turnover of meiotic and cell-fate regulators explains pleiotropic 1-cell defects | MEI-1, OMA-1, PIE-1, MEX-5, POS-1; specific sites variably defined in later work (pqac-00000005, pqac-00000000) | Maternal-effect genetics; suppression by mei-1 depletion; reporter analysis | mbk-2 loss causes penetrant maternal-effect embryonic lethality; embryos complete meiosis and extrude two polar bodies but fail mitotic spindle formation because MEI-1 persists ectopically on the mitotic spindle; spindle defect is suppressed by mei-1 depletion (pqac-00000005) | Nishi, 2007. URL not available in gathered snippet; dissertation-like source summarized in evidence (pqac-00000005) |


*Table: This table compiles experimentally supported functional annotation for C. elegans MBK-2 (UniProt Q9XTF3), including substrates, phosphosites, regulatory mechanisms, localization dynamics, and key quantitative phenotypes. It is useful as a source-by-source evidence map for writing a rigorous gene function report.*