Jacobs J R, Goodman C S
Department of Biochemistry, Howard Hughes Medical Institute, University of California, Berkeley 94720.
J Neurosci. 1989 Jul;9(7):2412-22. doi: 10.1523/JNEUROSCI.09-07-02412.1989.
We have identified the neurons that pioneer the major CNS axon tracts in the Drosophila embryo and determined their trajectory and fasciculation choices using serial section electron microscopy. Although Drosophila pioneer neurons make choices similar to those of their grasshopper homologs, there are interesting differences that reflect the much smaller nervous system size and the much faster rate of development characteristic of Drosophila. For example, where 2 longitudinal tracts are pioneered independently in grasshopper, only one is formed in Drosophila. This change is due to a change in fasciculation affinity of the pCC growth cone. Additionally, the intersegmental (IS) nerve is pioneered by a different neuron in Drosophila (aCC) than in the grasshopper (U1) because the smaller Drosophila CNS places the IS nerve within filopodial reach of the aCC soma, while in the grasshopper it is not. Drosophila growth cones explore a much more confined neuropil volume than do grasshopper growth cones but can also sample a larger fraction of the CNS as well. For this reason, some cell-cell recognition events critical to pathfinding in the grasshopper embryo may not be as essential in Drosophila. Nevertheless, many specific cellular affinities have been retained through the evolutionary divergence of these 2 species.
我们已经鉴定出在果蝇胚胎中引导主要中枢神经系统轴突束的神经元，并使用连续切片电子显微镜确定了它们的轨迹和成束选择。虽然果蝇的先驱神经元做出的选择与它们的蝗虫同源物相似，但也存在一些有趣的差异，这些差异反映了果蝇神经系统小得多的尺寸以及快得多的发育速度。例如，在蝗虫中由两个独立的纵向束引导的区域，在果蝇中只形成一个。这种变化是由于pCC生长锥的成束亲和力发生了变化。此外，果蝇中的节间（IS）神经由与蝗虫（U1）不同的神经元（aCC）引导，因为较小的果蝇中枢神经系统使IS神经处于aCC胞体丝状伪足可及的范围内，而在蝗虫中则不是。果蝇的生长锥探索的神经纤维网体积比蝗虫的生长锥受限得多，但也能对更大比例的中枢神经系统进行采样。因此，一些对蝗虫胚胎中路径寻找至关重要的细胞间识别事件在果蝇中可能不那么重要。尽管如此，通过这两个物种的进化分歧，许多特定的细胞亲和力得以保留。
