Akiyama-Oda Y, Hosoya T, Hotta Y
Department of Physics, Graduate School of Science and Molecular Genetics Laboratory, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033 Japan.
Development. 1999 May;126(9):1967-74. doi: 10.1242/dev.126.9.1967.
In the development of the Drosophila central nervous system, some of the neuroblasts designated as neuroglioblasts generate both glia and neurons. Little is known about how neuroglioblasts produce these different cell types. NB6-4 in the thoracic segment (NB6-4T) is a neuroglioblast, although the corresponding cell in the abdominal segment (NB6-4A) produces only glia. Here, we describe the cell divisions in the NB6-4T lineage, following changes in cell number and cell arrangement. We also examined successive changes in the expression of glial cells missing (gcm) mRNA and protein, activity of which is known to direct glial fate from the neuronal default state. The first cell division of NB6-4T occurred in the medial-lateral orientation, and was found to bifurcate the glial and neuronal lineage. After division, the medial daughter cell expressed GCM protein to produce three glial cells, while the lateral daughter cell with no GCM expression produced ganglion mother cells, secondary precursors of neurons. Although gcm mRNA was present evenly in the cytoplasm of NB6-4T before the first cell division, it became detected asymmetrically in the cell during mitosis and eventually only in the medial daughter cell. In contrast, NB6-4A showed a symmetrical distribution of gcm mRNA and GCM protein through division. Our observations suggest that mechanisms regulating gcm mRNA expression and its translation play an important role in glial and neuronal lineage bifurcation that results from asymmetric cell division.
在果蝇中枢神经系统的发育过程中，一些被指定为神经胶质母细胞的神经母细胞既能产生神经胶质细胞，也能产生神经元。关于神经胶质母细胞如何产生这些不同类型的细胞，目前所知甚少。胸段的NB6-4（NB6-4T）是一种神经胶质母细胞，而腹段的相应细胞（NB6-4A）仅产生神经胶质细胞。在这里，我们描述了NB6-4T谱系中的细胞分裂情况，以及细胞数量和细胞排列的变化。我们还研究了神经胶质缺失（gcm）mRNA和蛋白质表达的连续变化，已知其活性可将神经胶质细胞的命运从神经元的默认状态引导出来。NB6-4T的第一次细胞分裂发生在内外侧方向，并且发现它将神经胶质细胞谱系和神经元谱系分开。分裂后，内侧子细胞表达GCM蛋白以产生三个神经胶质细胞，而不表达GCM的外侧子细胞产生神经节母细胞，即神经元的二级前体。虽然在第一次细胞分裂之前gcm mRNA均匀地存在于NB6-4T的细胞质中，但在有丝分裂期间它在细胞中不对称地被检测到，最终只在内侧子细胞中被检测到。相比之下，NB6-4A在分裂过程中gcm mRNA和GCM蛋白呈对称分布。我们的观察结果表明，调节gcm mRNA表达及其翻译的机制在由不对称细胞分裂导致的神经胶质细胞谱系和神经元谱系的分叉中起重要作用。
