Differention of the animal-vegetal axis in Xenopus laevis oocytes. I. Polarized intracellular translocation of platelets establishes the yolk gradient

Michael Danilchik, John C. Gerhart

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Abstract

The animal-vegetal axis of the oocyte of Xenopus laevis is recognizable not only by the pattern of surface pigmentation, but also by the distribution of yolk platelets, with the largest platelets ({reversed tilde equals}14 μm in diameter) and 70% of the total yolk protein localized in the vegetal hemisphere. We have used fluorescent and radioactive vitellogenins (yolk protein precursors) to study the spatial and temporal patterns of yolk deposition along this axis. We find that the rate of uptake of vitellogenin is nearly uniform over the surface of vitellogenic oocytes of all sizes. Once formed, yolk platelets in the animal hemisphere move inward, around the germinal vesicle, and into the central region of the vegetal hemisphere. Yolk platelets of the vegetal hemisphere do not actively move but are slowly displaced from the surface by successive layers of younger platelets arising and enlarging near the surface. The oldest yolk platelets, which arise circumcortically at the beginning of vitellogenesis in stage II and III oocytes, eventually come to reside in the vegetal hemisphere of stage VI oocytes, in the upper portion of the cup-shaped region of largest platelets. The vegetal hemisphere thus gains the majority of yolk protein by directed intracellular transport from the animal hemisphere adding to the amount directly sequestered by the vegetal hemisphere.

Original languageEnglish (US)
Pages (from-to)101-112
Number of pages12
JournalDevelopmental Biology
Volume122
Issue number1
DOIs
StatePublished - 1987
Externally publishedYes

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Xenopus laevis
Oocytes
Blood Platelets
Egg Proteins
Vitellogenins
Vitellogenesis
Protein Precursors
Pigmentation

ASJC Scopus subject areas

  • Developmental Biology

Cite this

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title = "Differention of the animal-vegetal axis in Xenopus laevis oocytes. I. Polarized intracellular translocation of platelets establishes the yolk gradient",
abstract = "The animal-vegetal axis of the oocyte of Xenopus laevis is recognizable not only by the pattern of surface pigmentation, but also by the distribution of yolk platelets, with the largest platelets ({reversed tilde equals}14 μm in diameter) and 70{\%} of the total yolk protein localized in the vegetal hemisphere. We have used fluorescent and radioactive vitellogenins (yolk protein precursors) to study the spatial and temporal patterns of yolk deposition along this axis. We find that the rate of uptake of vitellogenin is nearly uniform over the surface of vitellogenic oocytes of all sizes. Once formed, yolk platelets in the animal hemisphere move inward, around the germinal vesicle, and into the central region of the vegetal hemisphere. Yolk platelets of the vegetal hemisphere do not actively move but are slowly displaced from the surface by successive layers of younger platelets arising and enlarging near the surface. The oldest yolk platelets, which arise circumcortically at the beginning of vitellogenesis in stage II and III oocytes, eventually come to reside in the vegetal hemisphere of stage VI oocytes, in the upper portion of the cup-shaped region of largest platelets. The vegetal hemisphere thus gains the majority of yolk protein by directed intracellular transport from the animal hemisphere adding to the amount directly sequestered by the vegetal hemisphere.",
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AB - The animal-vegetal axis of the oocyte of Xenopus laevis is recognizable not only by the pattern of surface pigmentation, but also by the distribution of yolk platelets, with the largest platelets ({reversed tilde equals}14 μm in diameter) and 70% of the total yolk protein localized in the vegetal hemisphere. We have used fluorescent and radioactive vitellogenins (yolk protein precursors) to study the spatial and temporal patterns of yolk deposition along this axis. We find that the rate of uptake of vitellogenin is nearly uniform over the surface of vitellogenic oocytes of all sizes. Once formed, yolk platelets in the animal hemisphere move inward, around the germinal vesicle, and into the central region of the vegetal hemisphere. Yolk platelets of the vegetal hemisphere do not actively move but are slowly displaced from the surface by successive layers of younger platelets arising and enlarging near the surface. The oldest yolk platelets, which arise circumcortically at the beginning of vitellogenesis in stage II and III oocytes, eventually come to reside in the vegetal hemisphere of stage VI oocytes, in the upper portion of the cup-shaped region of largest platelets. The vegetal hemisphere thus gains the majority of yolk protein by directed intracellular transport from the animal hemisphere adding to the amount directly sequestered by the vegetal hemisphere.

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