Jesuthasan S, Stähle U
Max-Planck-Institut für Entwicklungsbiologie, Tübingen, Germany.
Curr Biol. 1997 Jan 1;7(1):31-42. doi: 10.1016/s0960-9822(06)00025-x.
The zebrafish is emerging as an important genetic system for the study of vertebrate development, and many zygotic mutations affecting embryogenesis have been isolated. The early events in development are under the control of maternal genes but are relatively unexplored. Here, the process of axis specification is investigated.
The vegetal pole of the zygote transiently contains a dense array of parallel microtubules, while microtubules near the equator are disorganized. Irradiation of the zygote with ultraviolet light disrupts the formation of the vegetal microtubule array and causes loss of the axis; brief treatment with nocodazole at this stage also causes defects in the axis. During cleavage stages, yolk cortical microtubules reorganize to form arrays that apparently extend from marginal blastomeres. Prolonged exposure to cold (18 degrees C) or incubation in nocodazole prior to the 32-cell stage disrupts cortical microtubules and causes premature formation of the yolk syncytial layer; these treatments also prevent formation of an axis, as indicated by the absence of goosecoid and forkhead2 expression and of translocation of beta-catenin into nuclei. Cortical microtubule arrays are required for the transport of particles from the vegetal hemisphere into marginal blastomeres, as shown by the movement of polystyrene beads; treatments that prevent axis formation also prevent the entry of beads into blastomeres.
To form an organizer, zebrafish blastomeres appear to require substances which are transported from the vegetal hemisphere of the yolk cell by cortical microtubules. Initial asymmetry appears dependent on an array of parallel microtubules at the vegetal pole.
斑马鱼正成为研究脊椎动物发育的重要遗传系统，许多影响胚胎发生的合子突变已被分离出来。发育早期事件受母体基因控制，但相对未被深入研究。在此，对轴形成过程进行了研究。
合子的植物极短暂地含有密集排列的平行微管，而赤道附近的微管则杂乱无章。用紫外线照射合子会破坏植物微管阵列的形成并导致轴的缺失；在此阶段用诺考达唑短暂处理也会导致轴的缺陷。在卵裂阶段，卵黄皮质微管重新组织形成明显从边缘卵裂球延伸的阵列。在32细胞阶段之前长时间暴露于低温（18摄氏度）或在诺考达唑中孵育会破坏皮质微管并导致卵黄合胞体层过早形成；这些处理也会阻止轴的形成，这表现为无 goosecoid 和 forkhead2 表达以及β-连环蛋白无法转运到细胞核中。如聚苯乙烯珠的移动所示，皮质微管阵列是将颗粒从植物半球运输到边缘卵裂球所必需的；阻止轴形成的处理也会阻止珠子进入卵裂球。
为了形成组织者，斑马鱼卵裂球似乎需要由皮质微管从卵黄细胞的植物半球运输的物质。最初的不对称似乎依赖于植物极的平行微管阵列。
