The mechanism and pattern of yolk consumption provide insight into embryonic nutrition in Xenopus
The mechanism and pattern of yolk consumption provide insight into embryonic nutrition in Xenopus
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DOI：
10.1242/dev.032425
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发表时间：
2009-05-01
期刊：
影响因子：
4.6
通讯作者：
Kirschner, Marc W.
中科院分区：
文献类型：
--
作者：
Jorgensen, Paul;Steen, Judith A. J.;Kirschner, Marc W.
人们对发育过程中新陈代谢如何变化知之甚少。对于大多数动物胚胎来说，蛋黄蛋白是营养的主要来源，特别是必需氨基酸。在鸡蛋中，蛋黄储存在称为蛋黄血小板 (YP) 的大型细胞器内。通过研究 YP，我们深入了解了非洲爪蛙 Xenopus laevis 的胚胎营养。两栖动物遵循祖先模式，所有胚胎细胞都从卵细胞质继承 YP。这些 YP 在胚胎发生过程中的某个时刻在细胞内被消耗，但尚不清楚卵黄消耗何时、何地或如何发生。我们通过对纯化的 YP 进行生化和质谱分析，鉴定出了新型卵黄蛋白 Seryp。在单个 YP 中，Seryp 比主要卵黄蛋白更早降解完成，从而为参与卵黄蛋白水解的 YP 提供分子标记。我们证明卵黄蛋白水解是一个量子过程，其中胚胎细胞内休眠的 YP 子集重新整合到内吞系统中并成为末端降解区室。蛋黄消耗是分化的最早方面之一。卵黄消耗率也具有高度的组织特异性，这表明早期两栖动物胚胎的营养是组织自主的。但卵黄消耗似乎并不是由胚胎细胞缩小到极小的尺寸引发的。青蛙胚胎为体内代谢分析提供了一个有前途的平台。
Little is known about how metabolism changes during development. For most animal embryos, yolk protein is a principal source of nutrition, particularly of essential amino acids. Within eggs, yolk is stored inside large organelles called yolk platelets (YPs). We have gained insight into embryonic nutrition in the African clawed frog Xenopus laevis by studying YPs. Amphibians follow the ancestral pattern in which all embryonic cells inherit YPs from the egg cytoplasm. These YPs are consumed intracellularly at some point during embryogenesis, but it was not known when, where or how yolk consumption occurs. We have identified the novel yolk protein Seryp by biochemical and mass spectrometric analyses of purified YPs. Within individual YPs, Seryp is degraded to completion earlier than the major yolk proteins, thereby providing a molecular marker for YPs engaged in yolk proteolysis. We demonstrate that yolk proteolysis is a quantal process in which a subset of dormant YPs within embryonic cells are reincorporated into the endocytic system and become terminal degradative compartments. Yolk consumption is amongst the earliest aspects of differentiation. The rate of yolk consumption is also highly tissue specific, suggesting that nutrition in early amphibian embryos is tissue autonomous. But yolk consumption does not appear to be triggered by embryonic cells declining to a critically small size. Frog embryos offer a promising platform for the in vivo analysis of metabolism.