Horabin J I, Schedl P
Department of Molecular Biology, Princeton University, New Jersey 08544.
Mol Cell Biol. 1993 Mar;13(3):1408-14. doi: 10.1128/mcb.13.3.1408-1414.1993.
In Drosophila melanogaster, sex determination in somatic cells is controlled by a cascade of genes whose expression is regulated by alternative splicing [B. S. Baker, Nature (London) 340:521-524, 1989; J. Hodgkin, Cell 56:905-906, 1989]. The master switch gene in this hierarchy is Sex-lethal. Sex-lethal is turned on only in females, and an autoregulatory feedback loop which controls alternative splicing maintains this state (L. R. Bell, J. I. Horabin, P. Schedl, and T. W. Cline, Cell 65:229-239, 1991; L. N. Keyes, T. W. Cline, and P. Schedl, Cell 68:933-943, 1992). Sex-lethal also promotes female differentiation by controlling the splicing of RNA from the next gene in the hierarchy, transformer. Sosnowski et al. (B. A. Sosnowski, J. M. Belote, and M. McKeown, Cell 58:449-459, 1989) have shown that the mechanism for generating female transformer transcripts is not through the activation of the alternative splice site but by the blockage of the default splice site. We have tested whether an activation or a blockage mechanism is involved in Sex-lethal autoregulation. The male exon of Sex-lethal with flanking splice sites was placed into the introns of heterologous genes. Our results support the blockage mechanism. The poly(U) run at the male exon 3' splice site is required for sex-specific splicing. However, unlike transformer, default splicing to the male exon is sensitive to the sequence context within which the exon resides. This and the observation that the splice signals at the exon are suboptimal are discussed with regard to alternate splicing.
在黑腹果蝇中，体细胞的性别决定由一系列基因控制，这些基因的表达通过可变剪接来调节[B.S.贝克，《自然》（伦敦）340:521 - 524，1989；J.霍奇金，《细胞》56:905 - 906，1989]。这一层次结构中的主开关基因是性致死基因（Sex-lethal）。性致死基因仅在雌性中开启，并且一个控制可变剪接的自动调节反馈环维持这种状态（L.R.贝尔、J.I.霍拉宾、P.谢德尔和T.W.克莱恩，《细胞》65:229 - 239，1991；L.N.凯斯、T.W.克莱恩和P.谢德尔，《细胞》68:933 - 943，1992）。性致死基因还通过控制层次结构中下一个基因——变异性状基因（transformer）的RNA剪接来促进雌性分化。索斯诺夫斯基等人（B.A.索斯诺夫斯基、J.M.贝洛特和M.麦基翁，《细胞》58:449 - 459，1989）已经表明，产生雌性变异性状基因转录本的机制不是通过激活可变剪接位点，而是通过阻断默认剪接位点。我们测试了性致死基因自动调节中涉及的是激活机制还是阻断机制。将带有侧翼剪接位点的性致死基因的雄性外显子置于异源基因的内含子中。我们的结果支持阻断机制。性特异性剪接需要雄性外显子3'剪接位点处的聚（U）序列。然而，与变异性状基因不同，默认剪接到雄性外显子对该外显子所在的序列上下文敏感。关于可变剪接，讨论了这一点以及外显子处的剪接信号次优的观察结果。
