Ubbels G A
Hubrecht Laboratory, Netherlands Institute for Developmental Biology, Utrecht, The Netherlands.
Cell Mol Life Sci. 1997 Apr;53(4):382-409. doi: 10.1007/pl00000613.
We aimed at understanding of formation and function of the "Nieuwkoop Centre" in embryonic pattern formation. Discussed are data on genesis of cytoplasmic localizations in ovarian oocytes, transient modifications of cytoskeletal structures creating cytoplasmic asymmetries in fertilized eggs, the axis determining "vegetal cortical rotation" and fate of distinct cells, as shown by injection of specific molecular markers into particular blastomeres at specific times. Egg rotation and centrifugation suggested that sperm that gravity cooperate in symmetrization of the axially symmetrical anuran egg. After fertilization in space or in a fast rotating clinostate, axis formation and embryonic development were normal although the blastocoel was transiently abnormal. Normal tadpoles came back on Earth after ovulation, fertilization and culture in space. They metamorphosed normally and got healthy Earth-born F1 offspring. We conclude that neither sperm nor gravity are required for determination of the bilateral symmetry in the embryo of Xenopus laevis. In normal development sperm and gravity, either alone or in collaboration, may overrule an initial bilaterality inherent to, the full-grown oocyte, residing in some still unidentified component(s)/or mechanisms.
我们旨在了解胚胎模式形成过程中“nieuwkoop中心”的形成和功能。讨论了关于卵巢卵母细胞中细胞质定位的起源数据、受精后卵中细胞骨架结构的短暂修饰导致细胞质不对称、轴决定“植物皮质旋转”以及不同细胞的命运，这是通过在特定时间向特定卵裂球注射特定分子标记来显示的。卵的旋转和离心表明精子和重力在轴向对称的无尾两栖类卵的对称化过程中协同作用。在太空或快速旋转的回转器中受精后，尽管囊胚腔暂时异常，但轴的形成和胚胎发育是正常的。排卵、受精和在太空培养后，正常的蝌蚪回到地球。它们正常变态并产生健康的地球出生的F1后代。我们得出结论，非洲爪蟾胚胎双侧对称的确定既不需要精子也不需要重力。在正常发育中，精子和重力单独或共同作用，可能会推翻成熟卵母细胞固有的初始双侧性，这种双侧性存在于一些仍未确定的成分或机制中。
