Tissue-specific metabolomic signatures for a doublesex model of reduced sexual dimorphism

Abstract

Sex has a major effect on the metabolome. However, we do not yet understand the degree to which differences in metabolism are associated with anatomical dimorphism and modulated by sex-specific tissues. In the fruit fly, Drosophila melanogaster, knocking out doublesex (dsx) gives rise to adults with intermediate sex characteristics. Here, we sought to determine the degree to which this key node in sexual development leads to sex differences (SD) in the metabolome. We measured 91 metabolites across three tissues, comparing sex-dimorphic flies with those of reduced dimorphism: dsx null flies. The abundance of 51% of metabolites (46/91) differed between wildtype XX and XY flies in at least one tissue. However, in dsx flies, we only observed a sex difference in kynurenate, suggesting that dsx plays a major role in SD in fly metabolism. Kynurenate was consistently higher in XX flies in both dsx flies and controls. We also observed tissue-specific effects in dsx flies. Sex dimorphism manifests in part through dimorphic growth of organs, and we find that dimorphic metabolites across the fly enriched the growth-related branched-chain amino acid and mammalian target of rapamycin pathways. Our findings demonstrate that sex dimorphism is accompanied by substantial effects on the metabolome throughout the body.

Keywords: Doublesex; Drosophila melanogaster; metabolomics; sex differences; sexual dimorphism.

Figure 1.

PCA of metabolome samples by tissue. PCA for (A) head tissue, (B) thorax tissue and (C) abdomen tissue. dsx null flies are coloured in orange, wildtype flies are coloured in brown. Triangles represent XX and squares represent XY fly samples.

Figure 2.

Density of sex effect sizes across metabolites in wildtype and dsx null sexes. (A) Density plot across SD metabolites, those metabolites with a significant effect of sex in wildtype flies (n = 46 metabolites). Sex effect sizes across metabolites are significantly different between wildtype and dsx null groups: head (p = 0.002), thorax (p = 3 × 10^-4) and abdomen (p = 1 × 10^-6). (B) Density plot across all metabolites (n = 91 metabolites). Sex effect sizes across metabolites are significantly different between wildtype and dsx null groups: head (p = 0.007), thorax (p = 0.02), abdomen (p = 6x10^-4). Vertical lines mark the median (dashed) and mean (solid) effect size across metabolites. Effect sizes are plotted as absolute values on a log₁₀ scale.

Figure 3.

Tissue specificity of SD metabolites. (A) Venn diagram of number of SD metabolites that overlap across tissues. (B) Sex effect sizes for seven SD metabolites were significantly different between wildtype sexes across all three tissues. Effect sizes are calculated from the TukeyHSD function in R. Kynurenate, in light green, is the one metabolite that maintains a significant sex difference in both wildtype and dsx null flies across all three tissues. Effect sizes are plotted on a log10 scale.