Effects of Altering Insulin Signaling Pathway Genes on Sex Specific Growth in Drosophila melanogaster

Introduction: The mechanisms of growth and development are becoming better understood by studying Drosophila melanogaster. Although the presence of two major nutrient-sensing pathways and their intracellular signaling molecules have been identified, sex-specific effects of altering these pathways are poorly understood. This study aims to confirm the expression patterns of 5 GAL4 strains (r4, PPL, Lsp, da, nubbin) with green fluorescent protein (GFP), and observe the sex-specific phenotypic responses in a tissue-specific and systemic manner.  Methods: Each GAL4 strain was crossed with a UAS-GFP NLS (upstream activation sequence-nuclear localization sequence) reporter to view GFP expression patterns and to UAS-insulin receptor dominant negative (InR DN) and constitutively active (InR CA) reporters to assess phenotypic response. Results: It was observed that all 5 GAL4 strains exhibited expression patterns consistent with their tissue specific promoters. In addition, when all 5 GAL4 strains were crossed with the UAS-InR DN and UAS-InR CA, sex-specific phenotypic responses were observed in terms of tissue-specific and systemic growth, by measuring wing size and thorax length, respectively.  Discussion: Confirming the expression patterns of all 5 GAL4 strains is necessary when looking at tissue-specific and systemic phenotypic responses, as it ensures that phenotypic responses are due to altering of InR and not of non-functioning GAL4 strains themselves. Interestingly, the mean thorax lengths for the InR CA were consistently smaller than the InR DN for all GAL4 strains.  Conclusion: Although this study found promising results, more research is required to truly understand sexual size dimorphism in growth patterns. A next step is using the UAS-GAL4 system to alter genes of other signaling molecules within the IIS or TOR pathway. By looking at different key players within the pathway, we can understand how all these molecules work together and which ones have a greater sex-specific effect.