Molecular mechanisms of central nervous system formation

本研究的主要成果总结如下：1)我们首先分离并鉴定了鹰，编码果蝇中类固醇受体超家族的一个成员。在中枢神经系统中，eagle RNA在有限数量的细胞中表达，在第10期和第11期，在NB2-4、NB3-3、NB6-4和NB7-3 4种神经母细胞中观察到eagle RNA表达。除NB6-4外，鹰RNA的表达量在表达初期和成神经细胞分层时期达到最大值。在NB7-3的几个推定后代中，在11期后期和12期也观察到弱鹰RNA表达。在第13期，腹部段的鹰RNA全部消失。以鹰-激酶蛋白- lacz融合基因为报告基因，对鹰阳性细胞及其衍生物的迁移、迁移和轴突发生进行了研究。在第14期，检测到几种类型的神经或胶质细胞，包括EG和EW中间神经元连接到前后commre，更活跃的是…eagle表达缺失导致相当一部分eagle- kinesin - lacz阳性神经元轴突发生改变。部分EG细胞未能获得神经命运或分化极度延迟，而EW神经元产生方向异常的神经突，提示eagle可能在eagle阳性神经母细胞后代的发育中起关键作用。2) hedgehog基因产物由表达印迹的神经外胚层分泌，是2、5、6行s1后神经母细胞形成所必需的。刺猬蛋白不仅作为旁分泌因子，而且作为一种自分泌因子，它在神经母细胞分层前1-2小时（18‰）在神经外胚层上的短暂作用是形成正常神经母细胞所必需和充分的。与表皮发育相反，成神经细胞形成所需的hedgehog基因表达既不受缠绕也不受无翅调节。刺猬和无翅几乎同时向S2-S4神经母细胞的神经外胚层区域提供复合位置信号，因此，不同排的s1后神经母细胞可以沿着前后轴获得不同的位置值。每3个eagle阳性的S4-S5神经母细胞的前膜细胞数平均为5-9个，S1 NBs也是如此。与无翅的神经母细胞一样，某些S1后神经母细胞在假定的前膜区域的huckbein表达受hedgehog基因的控制。在NB7-3的形成过程中，hedgehog基因和无翅基因参与了独立的、平行的通路，其中一方的缺失由另一方弥补。NBs 6-4和7-3源于engriled结构域，也被两个同源盒基因（goose - berry-distal和engrailed）的差异表达所指定。少

Main outcomes of this research are summarized as follows. 1) We first isolated and characterized the eagle, encoding a member of the steroid receptor superfamily in Drosophila. ln the central nervous system, eagle RNA was expressed in a 1imited number of cells, Durning stages 10 and 11, eagle RNA expression was observed in four neuroblasts, NB2-4, NB3-3, NB6-4 and NB7-3. Except for NB6-4, eagle RNA expression reached a maximum at the very begining of expression or in the period of neuroblast delamination. Weak eagle RNA expression was also observed in a few putative progeny of NB7-3 during stages, late 11 and 12. All eagle RNA in abdominal segments disappeared at stage 13. Using an eagle-kinesin-lacZ fusion gene as a reporter, the dlvision, migration, and axonogenesis in eagle-positive cells and their derivatives were examined. At stage 14, several tyeps of neural or glial cells were detected which include EG and EW interneurons joining to the anteior and posterior commissures, respect … More ively. Lack of eagle expression caused altered axonogenesis in an appreciable fraction of eagle-Kinesin-LacZ-positive neurons. Some EG cells failed to acquire the neural fate or underwent an extremely delayd differentiation, while EW neurons produced neurites in abnormal directions, suggestng that eagle may Play a critical role in development of the progeny of eagle-positive neroblasts. 2) The hedgehog gene product, secreted from engrailed-expressing neuroectoderm, is required for the formation of post-S1 neuroblasts in rows 2,5 and 6. The hedgehog protein functions not only as a paracrine but also as anautocrine factor and its transient action on the neuroectoderm 1-2 hours (at 18ﾟC)prior to neuroblast delaminationis necessary and sufficient to form normal neuroblasts. In contrast to epidermal development, hedgehog expression required for neuroblast formation is regulated by neither engrailed nor wingless. hedgehog and wingless bestow composite positional cues on the neuroectodermal regions for S2-S4 neuroblasts at virtually the same time and, consequently, post-S1 neuroblasts in different rows can aquire different positional values along the anterior-posterior axis. The average number of proneural cells for each three eagle-positive S4-S5 neuroblasts was found to be 5-9, the same for S1 NBs, As with wingless, huckbein exprssion in putative proneural regions for certain post-S1 neuroblasts is under the control of hedgehog. hedgehog and wingless are involved in separate, paralle l pathways and loss of either is compensated for by the other in NB7-3, formation. NBs 6-4 and 7-3, arising from the engrailed domain, were also found to be specified by the differential expression of two homeobox genes, gooseberry-distal and engrailed. Less