Klingler M, Erdélyi M, Szabad J, Nüsslein-Volhard C
Max-Planck-Institut für Entwicklungsbiologie, Tübingen, FRG.
Nature. 1988 Sep 15;335(6187):275-7. doi: 10.1038/335275a0.
The formation of the unsegmented terminal regions of the Drosophila larva, acron and telson requires the function of at least five maternal genes (terminal genes class). In their absence, the telson and acron are not formed. One of them, torso (tor), has gain-of-function alleles which have an opposite phenotype to the lack-of-function (tor-) alleles: the segmented regions of the larval body, thorax and abdomen, are missing, whereas the acron is not affected and the telson is enlarged. In strong gain-of-function mutants, the pair-rule gene fushi tarazu (ftz) is not expressed, demonstrating the suppression of the segmentation process in an early stage of development. The tor gain-of-function effect is neutralized, and segmentation is restored in double mutants with the zygotic gene tailless (tll), which has a phenotype similar (but not identical) to that of tor-. This suggests that tor acts through tll, and that in the gain-of-function alleles of tor, the tll gene product is ectopically expressed at middle positions of the embryo, where it inhibits the expression of segmentation genes like ftz.
果蝇幼虫不分节的末端区域，即头部顶端和尾节的形成，至少需要五个母体基因（末端基因类）的功能。如果没有这些基因，尾节和头部顶端就不会形成。其中一个基因，躯干基因（tor），具有功能获得性等位基因，其表型与功能缺失（tor-）等位基因相反：幼虫身体的分节区域，即胸部和腹部缺失，而头部顶端不受影响，尾节增大。在强功能获得性突变体中，体节极性基因分节缺失（ftz）不表达，这表明在发育早期分节过程受到抑制。tor功能获得性效应在与合子基因无尾基因（tll）的双突变体中被中和，分节得以恢复，tll的表型与tor-相似（但不完全相同）。这表明tor通过tll起作用，并且在tor的功能获得性等位基因中，tll基因产物在胚胎的中间位置异位表达，在那里它抑制像ftz这样的分节基因的表达。
