Sexual dimorphisms in body size are widespread throughout the animal kingdom but their underlying mechanisms are not well characterized. Most models for how sex chromosome genes specify size dimorphism have emphasized the importance of gonadal hormones and cell-autonomous influences in mammals versus strictly cell-autonomous mechanisms in Drosophila melanogaster. Here, we use tissue-specific genetics to investigate how sexual size dimorphism (SSD) is established in Drosophila. We find that the larger body size characteristic of Drosophila females is established very early in larval development via an increase in the growth rate per unit of body mass. We demonstrate that the female sex determination gene, Sex-lethal (Sxl), functions in central nervous system (CNS) neurons as part of a relay that specifies the early sex-specific growth trajectories of larval but not imaginal tissues. Neuronal Sxl acts additively in 2 neuronal subpopulations, one of which corresponds to 7 median neurosecretory cells: the insulin-producing cells (IPCs). Surprisingly, however, male-female differences in the production of insulin-like peptides (Ilps) from the IPCs do not appear to be involved in establishing SSD in early larvae, although they may play a later role. These findings support a relay model in which Sxl in neurons and Sxl in local tissues act together to specify the female-specific growth of the larval body. They also reveal that, even though the sex determination pathways in Drosophila and mammals are different, they both modulate body growth via a combination of tissue-autonomous and nonautonomous inputs.

身体大小上的性别双态现象在整个动物界都很普遍，但其潜在机制尚不十分清楚。大多数关于性染色体基因如何指定大小二态性的模型都强调了性腺激素和哺乳动物细胞自主影响与果蝇中严格的细胞自主机制的重要性。在这里，我们使用组织特异性遗传学来研究在果蝇中如何建立性大小双态性（SSD）。我们发现果蝇雌性的较大的体型特征是通过增加单位体重的生长速度在幼虫发育的早期就建立起来的。我们证明了女性性别决定基因，性致死（Sxl）在中枢神经系统（CNS）神经元中发挥功能，作为中继的一部分，中继指定了幼虫的早期特定性别生长轨迹，但未指定虚构组织。神经元Sxl在2个神经元亚群中发挥加性作用，其中一个对应于7个中位神经分泌细胞：胰岛素产生细胞（IPC）。然而，出人意料的是，尽管IPC产生的胰岛素样肽（Ilps）可能起较晚的作用，但它们似乎并没有参与早期幼体中SSD的建立。这些发现支持了一种中继模型，其中神经元中的Sxl和局部组织中的Sxl共同起作用，以指定幼虫体的雌性特异性生长。他们还揭示了，即使果蝇中的性别决定途径 与哺乳动物不同，它们都通过组织自主和非自主输入的组合来调节身体的生长。