Brand M, Jarman A P, Jan L Y, Jan Y N
Howard Huges Medical Institute, University of California, San Francisco, CA 94143-0724, USA.
Development. 1993 Sep;119(1):1-17. doi: 10.1242/dev.119.Supplement.1.
Neural precursor cells in Drosophila arise from the ectoderm in the embryo and from imaginal disc epithelia in the larva. In both cases, this process requires daughterless and the proneural genes achaete, scute and lethal-of-scute of the achaete-scute complex. These genes encode basic helix-loop-helix proteins, which are nuclear transcription factors, as does the asense gene of the achaete-scute complex. Our studies suggest that asense is a neural precursor gene, rather than a proneural gene. Unlike the proneural achaete-scute gene products, the asense RNA and protein are found in the neural precursor during its formation, but not in the proneural cluster of cells that gives rise to the neural precursor cell. Also, asense expression persists longer during neural precursor development than the proneural gene products; it is still expressed after the first division of the neural precursor. Moreover, asense is likely to be downstream of the proneural genes, because (1) asense expression is affected in proneural and neurogenic mutant backgrounds, (2) ectopic expression of asense protein with an intact DNA-binding domain bypasses the requirement for achaete and scute in the formation of imaginal sense organs. We further note that asense ectopic expression is capable of initiating the sense organ fate in cells that do not normally require the action of asense. Our studies therefore serve as a cautionary note for the inference of normal gene function based on the gain-of-function phenotype after ectopic expression.
果蝇中的神经前体细胞起源于胚胎中的外胚层以及幼虫中的成虫盘上皮。在这两种情况下，这个过程都需要无女儿基因以及achaete - scute复合体中的原神经基因achaete、scute和scute致死基因。这些基因编码基本的螺旋 - 环 - 螺旋蛋白，它们是核转录因子，achaete - scute复合体中的asense基因也是如此。我们的研究表明，asense是一个神经前体基因，而不是原神经基因。与原神经achaete - scute基因产物不同，asense RNA和蛋白在神经前体形成过程中存在于神经前体中，但不存在于产生神经前体细胞的原神经细胞簇中。此外，在神经前体发育过程中，asense的表达比原神经基因产物持续的时间更长；在神经前体第一次分裂后它仍有表达。而且，asense可能位于原神经基因的下游，因为：（1）在原神经和神经genic突变背景下，asense的表达会受到影响；（2）具有完整DNA结合结构域的asense蛋白的异位表达绕过了成虫感觉器官形成过程中对achaete和scute的需求。我们还注意到，asense异位表达能够在通常不需要asense作用的细胞中启动感觉器官命运。因此，我们的研究为基于异位表达后的功能获得表型推断正常基因功能提供了一个警示。
