Sexual size dimorphism (SSD), a sex difference in body size, is widespread throughout the animal kingdom, raising the question of how sex influences existing growth regulatory pathways to bring about SSD. In insects, somatic sexual differentiation has long been considered to be controlled strictly cell-autonomously. Here, we discuss our surprising finding that in Drosophila larvae, the sex determination gene Sex-lethal (Sxl) functions in neurons to non-autonomously specify SSD. We found that Sxl is required in specific neuronal subsets to upregulate female body growth, including in the neurosecretory insulin producing cells, even though insulin-like peptides themselves appear not to be involved. SSD regulation by neuronal Sxl is also independent of its known splicing targets, transformer and msl-2, suggesting that it involves a new molecular mechanism. Interestingly, SSD control by neuronal Sxl is selective for larval, not imaginal tissue types, and operates in addition to cell-autonomous effects of Sxl and Tra, which are present in both larval and imaginal tissues. Overall, our findings add to a small but growing number of studies reporting non-autonomous, likely hormonal, control of sex differences in Drosophila, and suggest that the principles of sexual differentiation in insects and mammals may be more similar than previously thought.

性大小二态性（SSD）是一种身体大小上的性别差异，在整个动物界都很普遍，这引发了一个问题，即性别如何影响现有的生长调节途径以产生SSD。在昆虫中，长期以来一直认为体细胞性分化是严格由细胞自主控制的。在这里，我们讨论了令人惊讶的发现，即在果蝇幼虫中，性别决定基因Sex-lethal（Sxl）在神经元中的功能以非自治方式指定SSD。我们发现，在特定的神经元亚群中，Sxl是必需的，以上调女性身体的生长，包括在分泌神经分泌胰岛素的细胞中，即使胰岛素样肽本身似乎不参与其中。神经元Sxl对SSD的调节也独立于其已知的剪接靶标，变压器和msl-2，表明它涉及一种新的分子机制。有趣的是，由神经元Sxl控制的SSD对幼虫具有选择性，而不对虚构的组织类型具有选择性，并且除了存在于幼虫和虚构组织中的Sxl和Tra的细胞自主效应外，还可以发挥作用。总体而言，我们的发现增加了少量但不断增多的研究，这些研究报告了果蝇性别差异的非自主性，可能是激素性控制，并且表明昆虫和哺乳动物的性别分化原理可能比以前认为的更相似。