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#gray crescent

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amphibian Development-l

The gray crescent forms:

Following sperm entry, a parallel array of microtubules assembles in vegetal cortex and motor proteins drive rotation of outer cortical cytoplasm about thirty degrees relative to inner cytoplasm. This cortical rotation translocates maternal dorsal determinants including Dishevelled, GBP, and Wnt11 RNA toward the side opposite sperm penetration. The less pigmented area appearing there is called gray crescent, marking future dorsal side. It accumulates stabilized beta-catenin essential for Nieuwkoop center formation, organizer gene expression, and dorsal lip development. Position predicts embryonic axis.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 7: Axis specification cortical rotation and gray crescent formation.

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amphibian -ll

The gray crescent in amphibians forms:

Upon fertilization, sperm entry triggers calcium wave and formation of microtubule array from sperm aster at vegetal cortex. Dynein-dependent cortical rotation shifts vegetal cortex 30 degrees relative to inner cytoplasm, transporting dorsal determinants like Dishevelled, GBP and Wnt11 mRNA toward opposite side of sperm entry. This opposite side shows depigmentation as melanosomes move, forming gray crescent rich in beta-catenin stabilizing factors. Future dorsal organizer arises there. Sperm entry thus defines ventral pole, gray crescent dorsal pole marking organizer position for gastrulation patterning.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 9: Gray crescent formation opposite point of sperm entry via cortical rotation.

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