de Saint Phalle B, Sullivan W
Department of Biology, University of California, Santa Cruz, California 95064, USA.
J Cell Biol. 1998 Jun 15;141(6):1383-91. doi: 10.1083/jcb.141.6.1383.
In Sciara, unfertilized embryos initiate parthenogenetic development without centrosomes. By comparing these embryos with normal fertilized embryos, spindle assembly and other microtubule-based events can be examined in the presence and absence of centrosomes. In both cases, functional mitotic spindles are formed that successfully proceed through anaphase and telophase, forming two daughter nuclei separated by a midbody. The spindles assembled without centrosomes are anastral, and it is likely that their microtubules are nucleated at or near the chromosomes. These spindles undergo anaphase B and successfully segregate sister chromosomes. However, without centrosomes the distance between the daughter nuclei in the next interphase is greatly reduced. This suggests that centrosomes are required to maintain nuclear spacing during the telophase to interphase transition. As in Drosophila, the initial embryonic divisions of Sciara are synchronous and syncytial. The nuclei in fertilized centrosome-bearing embryos maintain an even distribution as they divide and migrate to the cortex. In contrast, as division proceeds in embryos lacking centrosomes, nuclei collide and form large irregularly shaped nuclear clusters. These nuclei are not evenly distributed and never successfully migrate to the cortex. This phenotype is probably a direct result of a failure to form astral microtubules in parthenogenetic embryos lacking centrosomes. These results indicate that the primary function of centrosomes is to provide astral microtubules for proper nuclear spacing and migration during the syncytial divisions. Fertilized Sciara embryos produce a large population of centrosomes not associated with nuclei. These free centrosomes do not form spindles or migrate to the cortex and replicate at a significantly reduced rate. This suggests that the centrosome must maintain a proper association with the nucleus for migration and normal replication to occur.
在果蝇中，未受精的胚胎在没有中心体的情况下启动孤雌生殖发育。通过将这些胚胎与正常受精胚胎进行比较，可以在有或没有中心体的情况下检查纺锤体组装和其他基于微管的事件。在这两种情况下，都形成了功能性有丝分裂纺锤体，它们成功地经历后期和末期，形成由中间体隔开的两个子核。没有中心体组装的纺锤体是无星纺锤体，其微管可能在染色体处或附近成核。这些纺锤体经历后期B并成功分离姐妹染色体。然而，没有中心体，下一个间期子核之间的距离会大大缩短。这表明在末期到间期的转变过程中，中心体是维持核间距所必需的。与果蝇一样，果蝇的初始胚胎分裂是同步的且为多核体。有中心体的受精胚胎中的细胞核在分裂并迁移到皮层时保持均匀分布。相比之下，在缺乏中心体的胚胎中，随着分裂的进行，细胞核会碰撞并形成大的不规则形状的核簇。这些细胞核分布不均匀，也从未成功迁移到皮层。这种表型可能是缺乏中心体的孤雌生殖胚胎中未能形成星体微管的直接结果。这些结果表明，中心体的主要功能是在多核体分裂期间提供星体微管，以实现适当的核间距和迁移。受精的果蝇胚胎会产生大量与细胞核无关的中心体。这些游离的中心体不会形成纺锤体或迁移到皮层，并且复制速度显著降低。这表明中心体必须与细胞核保持适当的关联才能发生迁移和正常复制。
