#EMS blastomere

C-Elegans Development-l

Which signaling molecule helps distinguish MS and E lineages in EMS blastomere?

EMS blastomere division into MS mesoderm and E endoderm requires polarized Wnt signaling from P2 integrating cell polarity. P2 secretes MOM-2 Wnt, MOM-5 Frizzled, MES-1 immunoglobulin transmembrane signals activating Wnt/beta-catenin asymmetry pathway: WRM-1 beta-catenin, LIT-1 Nemo-like kinase and KIN-19 phosphorylate POP-1 TCF, exporting it from E nucleus via WRM-1 complex and reducing nuclear level. Low POP-1 plus high SKN-1 allows MED-1/2 and END-1/3 expression specifying endoderm in E, while high POP-1 in MS represses endoderm and promotes mesoderm genes tbx-35.

Ref: Thorpe et al., Cell 1997: MOM-2 Wnt signaling distinguishes MS and E fates downstream of EMS.

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C-Elegans Development-l

Which transcription factor is required for EMS blastomere fate in C. elegans?

SKN-1 is bZip transcription factor related to mammalian Nrf2, maternally provided and enriched in EMS and P2 via post-translational regulation and Wnt asymmetry. In EMS blastomere, SKN-1 directly activates MED-1,2 GATA factors and END-1,3 endoderm determinants leading to mesendoderm specification and tbx-35 muscle regulator. Nuclear entry depends on phosphorylation and redox sensing. Loss abolishes MS-derived pharynx, anterior body muscle, plus E-derived intestine causing embryonic lethality. It integrates maternal polarity, MET-2, and P2 inductive inputs ensuring EMS produces both mesoderm an

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 8: SKN-1 transcription factor specifying EMS mesendoderm fate.

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Elegans -ll

What determines the default fate of EMS blastomere?

EMS blastomere default state without P2 signal is mesodermal MS fate. This is determined by nuclear POP-1 levels. In anterior MS daughter, high nuclear POP-1 binds and represses end-1 promoter together with histone deacetylases, allowing tbx-35 for pharynx and muscle. Low POP-1 permits endoderm. POP-1 repression defines default program: when Wnt signaling absent, both daughters maintain high POP-1 and become MS-like. SKN-1 provides competence for both MS and E, but fate choice gated by POP-1 differential. Therefore POP-1 concentration acts as binary switch establishing MS as ground state, repr

Ref: Lin et al. 1995; Gilbert Chapter 4: POP-1 determines default fate of EMS blastomere as MS.

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Elegans -ll

Which of the following is responsible for EMS blastomere specification in C. elegans?

EMS blastomere, daughter of P1, generates MS mesoderm and E endoderm. Its polarity depends on POP-1, C. elegans TCF transcription factor downstream of Wnt/MAPK signaling from P2. In anterior daughter MS, high nuclear POP-1 represses endoderm genes; in posterior E maintained in contact with P2, Wnt signal phosphorylates POP-1 lowering nuclear levels and converting it to activator cooperating with SKN-1 and MED factors to induce END-1/3. Loss of POP-1 causes both daughters to become E-like, showing POP-1 essential for EMS asymmetry and proper endomesoderm specification throughout intestine and p

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 4: EMS specification and POP-1 TCF role in C. elegans.

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