Cline T W
Dev Biol. 1983 Feb;95(2):260-74. doi: 10.1016/0012-1606(83)90027-1.
Regulation of Drosophila sex determination and X-chromosome dosage compensation in response to the X-chromosome/autosome (X/A) balance of the zygote is shown to require proper functioning of both the da+ gene in the mother and the Sxl+ gene in the zygote. Previous studies led to the hypothesis that zygotic Sxl+ alleles are differentially active in females (XXAA) vs males (XYAA) in response to the X/A balance, and that maternal da+ gene product acts as a positive regulator in this connection. Sxl+ activity was proposed to impose the female developmental sequence on cells which would follow the male sequence in its absence. Important predictions of this proposal are verified. This study focuses primarily on the phenotype of triploid intersexes (XXAAA, X/A = 0.67). They are shown here to survive effects of da and Sxl mutations that would be lethal to diploids. The ambiguous X/A signal of intersexes normally causes them to develop as phenotypic mosaics of male and female tissue. Loss of maternal da+ or zygotic Sxl+ gene function shifts their somatic sexual phenotype to the male alternative. A gain-of-function mutation at Sxl has the opposite effect, imposing female development regardless of the maternal genotype with respect to da. It also reduces their rate of X-linked gene expression. The effects of a duplication of Sxl+ resemble those of the constitutive Sxl allele, but are less extreme. The role of these genes in the process of X-chromosome dosage compensation is inferred indirectly from the strict dependence of the mutations' lethal effects on the X/A balance in haploids, diploids, and triploids, and more directly from the effects of the mutations on the phenotypes of the X-linked neomorphic mutations, Bar and Hairy-wing. The relationship of da+ and Sxl+ gene functions to those of other sex-specific lethal loci in D. melanogaster, and to sex determination mechanisms in other species, is discussed.
果蝇性别决定和X染色体剂量补偿对合子X染色体/常染色体（X/A）平衡的调控显示，需要母体中的da+基因和合子中的Sxl+基因正常发挥作用。先前的研究提出了这样的假说：合子中的Sxl+等位基因根据X/A平衡在雌性（XXAA）和雄性（XYAA）中表现出不同的活性，并且母体da+基因产物在这一过程中起正调控作用。有人提出，Sxl+的活性会使细胞遵循雌性发育序列，而在没有它的情况下细胞会遵循雄性序列。该假说的重要预测得到了验证。本研究主要关注三倍体雌雄间性（XXAAA，X/A = 0.67）的表型。结果表明，它们能在对二倍体致死的da和Sxl突变的影响下存活。雌雄间性模糊的X/A信号通常会使其发育为雄性和雌性组织的表型嵌合体。母体da+或合子Sxl+基因功能的丧失会使其体细胞性表型转变为雄性。Sxl的功能获得性突变则有相反的效果，无论母体关于da的基因型如何，都会使发育为雌性。它还会降低其X连锁基因的表达速率。Sxl+重复的影响类似于组成型Sxl等位基因，但程度较轻。这些基因在X染色体剂量补偿过程中的作用是通过单倍体、二倍体和三倍体中突变致死效应严格依赖于X/A平衡间接推断出来的，更直接地是通过突变对X连锁新形态突变体Bar和毛翅的表型影响推断出来的。本文还讨论了da+和Sxl+基因功能与黑腹果蝇其他性别特异性致死位点的功能以及其他物种性别决定机制的关系。
