Fischer-Vize J A, Vize P D, Rubin G M
Howard Hughes Medical Institute, Department of Molecular and Cellular Biology, University of California, Berkeley 94720.
Development. 1992 May;115(1):89-101. doi: 10.1242/dev.115.1.89.
An unusual recessive allele of the Drosophila groucho gene, which encodes a transducin-like protein, affects the fates of specific cells in the eye disc. groucho is one of several transcription units in the Enhancer of split complex. Most groucho mutations are zygotic lethal due to the proliferation of embryonic neural cells at the expense of epidermal cells. In contrast, flies homozygous for the mutant allele described here, groBFP2, are viable but have abnormal eyes. The Drosophila compound eye is composed of several hundred identical facets, or ommatidia, each of which contains eight photoreceptor cells, R1-R8. In groBFP2 mutant retinas, most of the facets contain eight normally determined photoreceptor cells and one or two additional R-cells of the R3/4 subtype. The extra photoreceptors appear to arise from the mystery cells, which are part of the precluster that initiates the ommatidium, but do not normally become neurons. groBFP2 behaves as a partial loss-of-function mutant. Analysis of ommatidia mosaic for wild-type and groBFP2 mutant cells suggests that the focus of action of the groBFP2 mutation is outside of the photoreceptor cells. These results imply that one function of groucho is in a pathway whereby neuralization of the mystery cells is inhibited by other non-neural cells in the eye disc. In addition, determination of R3/4 photoreceptors usually requires contact with R2 and R5. Specification of the mystery cells as ectopic R3/4 subtype photoreceptors in groBFP2 mutant eye discs implies that induction by R2 or R5 is not absolutely necessary for R3/4 cell determination.
果蝇groucho基因的一个罕见隐性等位基因编码一种转导蛋白样蛋白，它影响眼盘中特定细胞的命运。groucho是分裂复合物增强子中的几个转录单位之一。大多数groucho突变是合子致死的，因为胚胎神经细胞的增殖是以牺牲表皮细胞为代价的。相比之下，此处描述的突变等位基因groBFP2的纯合果蝇是可存活的，但眼睛异常。果蝇复眼由数百个相同的小眼面或小眼组成，每个小眼面包含八个光感受器细胞，R1 - R8。在groBFP2突变体视网膜中，大多数小眼面包含八个正常确定的光感受器细胞以及一两个额外的R3/4亚型R细胞。额外的光感受器似乎源自神秘细胞，这些细胞是启动小眼的前簇的一部分，但通常不会变成神经元。groBFP2表现为部分功能丧失突变体。对野生型和groBFP2突变体细胞的小眼镶嵌分析表明，groBFP2突变的作用焦点在光感受器细胞之外。这些结果表明，groucho的一个功能是参与一条途径，通过该途径眼盘中的其他非神经细胞抑制神秘细胞的神经化。此外，R3/4光感受器的确定通常需要与R2和R5接触。在groBFP2突变体眼盘中，神秘细胞被指定为异位R3/4亚型光感受器，这意味着R2或R5的诱导对于R3/4细胞的确定并非绝对必要。
