果蝇胚胎发育与前-后轴.pptVIP

在受精卵的中央，细胞核进行多次有丝分裂。果蝇受精卵平均每8分钟一次核分裂，形成多大256个细胞核。之后细胞核移动到受精卵的外围，继续进行有丝分裂。 在第九个分裂周期中，大约五个细胞核到达胚胎的后极表面，开始被细胞膜包围，这些极细胞将来形成成虫的配子。 大多数其他的细胞核在第十分裂周期到达胚胎的外围，之后经历减慢的四个分裂周期。细胞核经过这些分裂阶段，胚胎被称作合包体胚层（syncytial blastoderm）。 合包体胚层时期，所有的细胞核公用一个细胞质，没有其他细胞膜存在。(后图所示) During these stages of nuclear division, the embryo is called a syncytial blastoderm, meaning that all the cleavage nuclei are contained within a common cytoplasm. No cellmembranes exist other than that of the egg itself. 尽管所有的核公用一个细胞质，并不是意味着每个细胞核周围的细胞质是一样的。每一个核周围都包含细胞骨架蛋白。在第十个周期，各个细胞核到达卵的外围时，每一个受精卵周围都包围着微管和微丝。细胞核和它们周围的细胞质被称作活质体（energids） Although the nuclei divide within a common cytoplasm, this does not mean that the cytoplasm is itself uniform. Karr and Alberts (1986) have shown that each nucleus within the syncytial blastoderm is contained within its own little territory of cytoskeletal proteins. When the nuclei reach the periphery of the egg during the tenth cleavage cycle, each nucleus becomes surrounded by microtubules and microfilaments. The nuclei and their associated cytoplasmic islands are called energids 第13周期后，受精卵细胞的细胞膜开始在细胞核之间折叠，最终将每一个细胞核分割成独立的细胞。这个过程产生细胞胚层cellular blastoderm，所有的细胞都沿着大量卵黄构成的核心周围单层排列。像其他细胞的形成一样，细胞胚层的形成涉及微管和微丝的微妙相互作用。 Following cycle 13, the oocyte plasma membrane folds inward between the nuclei,eventually partitioning off each somatic nucleus into a single cell . This process creates the cellular blastoderm, in which all the cells are arranged in a single-layered jacket around the yolky core of the egg . Like anyother cell formation, the formation of thelulablastoderm involves a delicate interplay between microtubules and microfilaments. 胚层的第一期细胞化特征是细胞膜内陷，位于细胞膜深层的肌动蛋白网进入核间区域并形成沟渠。上述过程可以被阻断微管的药物所阻断 The first phase of blastoderm cellularization is characterized by the invagination of cell membranes and their underlying actin microfilamentnetwork into the regions between the nuclei to form furrow canals.This process can be inhibited by drugs that block 细胞膜和肌动蛋白向深部延伸超越细胞核的所在水平，第二期细胞化开始。肌动蛋白-