No abstract

In Drosophila, changes to dietary protein elicit different body size responses between the sexes. Whether these differential body size effects extend to other macronutrients remains unclear. Here, we show that lowering dietary sugar (0S diet) enhanced body size in male and female larvae. Despite an equivalent phenotypic effect between the sexes, we detected sex-specific changes to signaling pathways, transcription, and whole-body glycogen and protein. In males, the low sugar diet augmented insulin/insulin-like growth factor signaling pathway (IIS) activity by increasing insulin sensitivity, where increased IIS was required for male metabolic and body size responses in 0S. In females reared on low sugar, IIS activity and insulin sensitivity were unaffected, and IIS function did not fully account for metabolic and body size responses. Instead, we identified a female-biased requirement for the target of rapamycin pathway in regulating metabolic and body size responses. Together, our data suggest the mechanisms underlying the low sugar-induced increase in body size are not fully shared between the sexes, highlighting the importance of including males and females in larval studies even when similar phenotypic outcomes are observed.

Word Count: 230 Word Count: 4037 Reference Count: 54 Figure Count: 5 AbstractHeterogeneity within specific cell types is common and increasingly apparent with the advent of single-cell transcriptomics. Transcriptional and functional cellular specialization has been described for insulin-secreting β-cells of the endocrine pancreas, including so-called extreme β-cells exhibiting >2 fold higher insulin gene activity. However, it is not yet clear whether β-cell heterogeneity is stable or reflects dynamic cellular states. We investigated the temporal kinetics of endogenous insulin gene activity using live-cell imaging, with complementary experiments employing FACS and single-cell RNA sequencing, in β-cells from Ins2 GFP knock-in mice. In vivo staining and FACS analysis of islets from Ins2 GFP mice confirmed that at a given moment, ~25% of β-cells exhibited significantly higher activity at the conserved insulin gene Ins2(GFP) HIGH . Live-cell imaging captured on and off 'bursting' behaviour in single β-cells that lasted hours to days. Single cell RNA sequencing determined that Ins2(GFP) HIGH βcells were enriched for markers of β-cell maturity and had reduced expression of anti-oxidant genes. Ins2(GFP) HIGH β-cells were also significantly less viable at all glucose concentrations and in the context of ER stress. Collectively, our results demonstrate that the heterogeneity of extreme insulin production, observed in mouse and human β-cells, can be accounted for by dynamic states of insulin gene activity. Our observations define a previously uncharacterized form of β-cell plasticity. Understanding the dynamics of insulin production has relevance for understanding the pathobiology of diabetes and for regenerative therapy research.

The rising incidence of pancreatic cancer is largely driven by increased prevalence of obesity and type 2 diabetes (T2D). Hyperinsulinemia is a cardinal feature of obesity and T2D, and is associated with increased cancer incidence and mortality. Genetic reduction of insulin production suppresses formation of pancreatic intraepithelial neoplasia (PanIN) pre-cancerous lesions in mice with mutant Kras. However, it remained unclear whether hyperinsulinemia exerts its tumorigenic effects directly on the cells that give rise to PanINs or indirectly on the tumor microenvironment. Here, we tested whether diet-induced hyperinsulinemia contributes to pancreatic cancer directly through insulin receptor (Insr) signaling in KrasG12D-expressing pancreatic acinar cells. Loss of insulin receptors in wild-type or KrasG12D-expressing acinar cells did not significantly influence fasting glucose or insulin. Strikingly, mice lacking Insr in KrasG12D-expressing acinar cells and their progeny had a significant reduction in PanIN plus tumor area in males (2.7-fold) and females (5.3-fold) compared to control mice. Mechanistically, proteome analyses implicated a reduction in digestive enzymes among altered protein networks in mice protected from PanINs, and together with phospho-proteome analysis, linked the spliceosome, ribosome, and secretory pathway to insulin signaling in context of pancreatic cancer initiation. Collectively, these data demonstrate that insulin receptor signaling in acinar cells promotes PanIN initiation in the context of obesity.

Transcriptional and functional cellular specialization has been described for insulin-secreting β-cells of the endocrine pancreas. However, it is not clear whether β-cell heterogeneity is stable or reflects dynamic cellular states. We investigated the temporal kinetics of endogenous insulin gene activity using live cell imaging, with complementary experiments employing FACS and single cell RNA sequencing, in β-cells from Ins2GFP knock-in mice. In vivo staining and FACS analysis of islets from Ins2GFP mice confirmed that at a given moment, ∼25% of β-cells exhibited significantly higher activity at the conserved insulin gene Ins2. Live cell imaging captured Ins2 gene activity dynamics in single β-cells over time. Autocorrelation analysis revealing a subset of cells with oscillating behavior, with oscillation periods of 17 hours. Increased glucose concentrations stimulated more cells to oscillate and resulted in higher average Ins2 gene activity per cell. Single cell RNA sequencing determined that Ins2(GFP)HIGH β-cells were enriched for markers of β-cell maturity. Ins2(GFP)HIGH β-cells were also significantly less viable at all glucose concentrations and in the context of ER stress. Collectively, our results demonstrate that the heterogeneity of insulin production, observed in mouse and human β-cells, can be accounted for by dynamic states of insulin gene activity.