Hartenstein V, Younossi-Hartenstein A, Lekven A
Department of Biology, University of California Los Angeles 90024.
Dev Biol. 1994 Oct;165(2):480-99. doi: 10.1006/dbio.1994.1269.
Cytoskeletal changes occurring during the delamination of precursors of the peripheral (microchaete precursors in the pupal notum) and central nervous system (embryonic SI neuroblasts) were studied. The pattern of cell division in the ventral neurectoderm (VN) of wild-type embryos was analyzed using BrdU incorporation and correlated to the pattern of neuroblast delamination. Finally, defects in the pattern of proliferation of the VN and neuroblast delamination which occur in Notch and wingless mutant embryos were described. The results indicate that the patterns of delamination and mitosis are closely correlated: delamination occurs either immediately after a cell has divided (in case of microchaete precursors) or shortly before the division (in case of the neuroblasts). In addition, cytoskeletal changes similar to those occurring during mitosis can be seen in delaminating neuronal precursors. Thus, during both mitosis and delamination, the discrete apicobasally oriented microfilament-tubulin bundles break down. Microfilaments form a dense, diffuse cortical layer surrounding the entire cell body. Microtubules are concentrated at the apically located centrosome. The relationship between mitosis and delamination is supported by the finding that the neurogenic gene Notch and segment polarity gene wingless (wg) affect both proliferation and delamination in the ventral neurectoderm. Thus, in embryos expressing the trunkated cytoplasmic domain of the neurogenic gene Notch under heat-shock control (Struhl et al., 1993), all ventral neurectodermal cells go into mitosis prematurely, followed by the absence of neuroblast delamination. In wg loss-of-function mutants, mitosis in the VN is irregular and generally postponed, accompanied by irregularities in the timing of neuroblast delamination in general and the absence of a subset of neuroblasts.
研究了外周神经系统（蛹期背板中的微刚毛前体）和中枢神经系统（胚胎期SI神经母细胞）前体分层过程中发生的细胞骨架变化。利用BrdU掺入法分析了野生型胚胎腹侧神经外胚层（VN）中的细胞分裂模式，并将其与神经母细胞分层模式相关联。最后，描述了Notch和无翅突变体胚胎中VN增殖模式和神经母细胞分层的缺陷。结果表明，分层和有丝分裂模式密切相关：分层要么在细胞分裂后立即发生（微刚毛前体的情况），要么在分裂前不久发生（神经母细胞的情况）。此外，在分层的神经元前体中可以看到与有丝分裂期间发生的细胞骨架变化相似的情况。因此，在有丝分裂和分层过程中，离散的顶基定向微丝 - 微管蛋白束都会分解。微丝形成围绕整个细胞体的致密、弥散的皮质层。微管集中在位于顶端的中心体处。有丝分裂和分层之间的关系得到了以下发现的支持，即神经发生基因Notch和节段极性基因无翅（wg）会影响腹侧神经外胚层中的增殖和分层。因此，在热休克控制下表达神经发生基因Notch截短细胞质结构域的胚胎中（Struhl等人，1993），所有腹侧神经外胚层细胞过早进入有丝分裂，随后神经母细胞分层缺失。在wg功能丧失突变体中，VN中的有丝分裂不规则且通常推迟，伴随着神经母细胞分层时间的不规则以及一部分神经母细胞的缺失。
