Sun Y, Jan L Y, Jan Y N
Howard Hughes Medical Institute, Departments of Physiology and Biochemistry, University of California, San Francisco, CA 94143-0725, USA.
Proc Natl Acad Sci U S A. 2000 Jun 6;97(12):6815-9. doi: 10.1073/pnas.110154497.
During development of the Drosophila peripheral nervous system, different proneural genes encoding basic helix-loop-helix transcription factors are required for different sensory organs to form. atonal (ato) is the proneural gene required for chordotonal organs and R8 photoreceptors, whereas the achaete-scute complex contains proneural genes for external sensory organs such as the macrochaetae, large sensory bristles. Whereas ectopic ato expression induces chordotonal organ formation, ectopic scute expression produces external sensory organs but not chordotonal organs in the wing. Proneural genes thus appear to specify the sensory organ type. In the ommatidium, or unit eye, R8 is the first photoreceptor to form and appears to recruit other photoreceptors and support cells. In the atonal(1) (ato(1)) mutant, R8 photoreceptors fail to form, thereby resulting in the complete absence of ommatidia. To our surprise, we found that ectopic scute expression in the ato(1) mutant induces the formation of ommatidia, which occasionally sprout ectopic macrochaetae. Remarkably, many scute-induced ommatidia lack R8 although they contain outer photoreceptors.
在果蝇外周神经系统发育过程中，不同的原神经基因（编码碱性螺旋-环-螺旋转录因子）对于不同感觉器官的形成是必需的。无调（atonal，ato）是弦音器官和R8光感受器所需的原神经基因，而achaete-scute复合体包含用于外部感觉器官（如大刚毛，大型感觉刚毛）的原神经基因。异位表达ato会诱导弦音器官形成，而异位表达scute则会在翅膀上产生外部感觉器官，但不会产生弦音器官。因此，原神经基因似乎决定了感觉器官的类型。在小眼（即单位眼）中，R8是第一个形成的光感受器，似乎会招募其他光感受器和支持细胞。在无调（1）（ato（1））突变体中，R8光感受器无法形成，从而导致小眼完全缺失。令我们惊讶的是，我们发现在ato（1）突变体中异位表达scute会诱导小眼形成，这些小眼偶尔会长出异位大刚毛。值得注意的是，许多由scute诱导形成的小眼虽然包含外部光感受器，但缺乏R8。
