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，它编码果蝇中类固醇受体超家族的一员。在中枢神经系统中，Eagle RNA仅在有限的细胞中表达，在第10和11期，在NB 2 -4、NB 3 -3、NB 6 -4和NB 7 -3四个神经母细胞中观察到Eagle RNA的表达。除NB 6 -4外，eagle RNA在表达初期或成神经细胞分层时表达最高。弱鹰RNA表达也观察到在几个推定的后代NB 7 -3在阶段，后期11和12。所有鹰RNA腹节在第13阶段消失。以eagle-kinesin-lacZ融合基因为报告基因，研究了eagle-kinesin-lacZ阳性细胞及其衍生物的分化、迁移和轴突生成。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连合和后连合， ...更多信息 ively。缺乏鹰的表达引起改变的轴突在鹰驱动蛋白LacZ阳性神经元的一个可观的分数。一些EG细胞未能获得神经命运或经历极其延迟的分化，而EW神经元以异常方向产生神经突起，这表明鹰可能在鹰阳性神经母细胞后代的发育中发挥关键作用。2)hedgehog基因产物，由表达nrailed的神经外胚层分泌，是形成第2、5和6行的后S1神经母细胞所必需的。hedgehog蛋白不仅作为旁分泌因子，而且作为自分泌因子，在神经母细胞脱层之前1-2小时（在18 ℃），其对神经外胚层的短暂作用是形成正常神经母细胞所必需的。与表皮发育相反，成神经细胞形成所需的hedgehog表达既不受enrailed也不受wingless的调控。hedgehog和wingless几乎同时在神经外胚层区域为S2-S4神经母细胞提供复合位置线索，因此，不同行中的后S1神经母细胞可以沿前后轴沿着获得不同的位置值。每三个鹰阳性的S_4-S_5神经母细胞的前神经细胞数平均为5-9个，S_1神经母细胞的前神经细胞数平均为5-9个。与无翅的情况一样，某些后S_1神经母细胞的前神经区的huckbein表达受hedgehog控制。hedgehog和wingless参与单独的、相互竞争的途径，并且在NB 7 -3形成中，任一个的损失由另一个补偿。NB 6-4和7-3，产生于enrailed域，也被发现是由两个同源异型盒基因，鹅莓远端和enrailed的差异表达指定。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