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#vegetal pole

2 public questions tagged with this topic.

Sea Urchin -ll

The vegetal pole micromeres at the 4th cleavage are formed by:

At fourth cleavage sea urchin vegetal blastomeres divide unequally unlike animal counterparts. While animal tier divides meridionally into eight mesomeres of similar size, vegetal tier undergoes unequal equatorial division producing four large macromeres and four very small micromeres clustered at vegetal pole. Unequal partitioning concentrates maternal determinants like Disheveled, vegetal polarity proteins, and specific mRNAs into micromeres, initiating skeletogenic lineage specification through β-catenin pathway. Equal equatorial cleavage would not generate size disparity, while meridional cleavage would maintain symmetry. Thus unequal equatorial cleavage uniquely defines micromere formation and organizer establishment.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 8: Fourth cleavage - formation of micromeres and macromeres.

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amphibian Development-l

The vegetal pole in amphibian eggs contains:

Amphibian eggs exhibit pronounced animal-vegetal polarity that influences cleavage. Animal hemisphere contains little yolk, abundant mitochondria, ribosomes, and divides rapidly into small micromeres that contribute mainly to ectoderm and nervous system. Vegetal hemisphere accumulates dense yolk platelets, glycogen, lipids, and maternal mRNAs such as VegT and Vg1, slowing cleavage and producing large macromeres. Heavy yolk physically hinders contractile ring constriction, lengthening cell cycle vegetally. This gradient creates unequal blastomere sizes, partitions endoderm determinants vegetally, and influences induction of mesoderm via Nodal signaling from vegetal cells to marginal zone.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 2: Vegetal yolk distribution and cleavage retardation.

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