Genetic mechanisms of signal integration in the nutrient sensing network

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PROJECT SUMMARY Eukaryotes have evolved complex signaling networks that assess internal energy and nutrient stores and respond to the available nutrients. In humans, inaccurate nutrient sensing can result in type II diabetes and obesity. Unfortunately, the therapeutic targets available to treat these diseases are limited. Cancer progression is promoted by changes in metabolism, since rapid growth of tumors is mediated by dysregulation of carbon, nitrogen, and phosphate utilization. A key knowledge gap is understanding how eukaryotic cells distinguish between available nutrients and integrate signals from diverse nutrient sensing pathways. Filling this gap may identify targets for future diabetes, obesity, or cancer therapeutics. Many nutrient sensing pathways used as therapeutic targets in humans were originally identified in eukaryotic microbes. However, much of this work focused on the model yeast Saccharomyces cerevisiae, which has a limited nutrient utilization repertoire. Eukaryotic microbes that utilize a more diverse set of nutrients employ additional mechanisms of nutrient sensing conserved in humans. To characterize novel conserved nutrient sensing regulatory mechanisms, this project focuses on defining the nutrient sensing network by investigating genes that integrate signaling pathways and distinguish between nutrient sources in eukaryotic microbes with unique phenotypic outputs. In response to available nutrients, the filamentous fungus Neurospora crassa exquisitely tailors the regulation of secreted enzymes with easily measurable activity. The oleaginous yeast Rhodosporidium toruloides accumulates lipids when carbon is abundant and nitrogen or phosphate limiting. To investigate how signaling networks are integrated, this project will use the easily scorable phenotypes of these two atypical model fungi to focus on two questions: (1) the mechanism by which signals are integrated between nutrient sensing pathways and the p38 mitogen activated protein kinase pathway, which regulates both nutrient utilization and stress, to achieve downstream responses specific to differing stimuli; and (2) the genetic mechanisms that integrate signals from carbon, nitrogen, and phosphate pathways. Many conserved pathways that regulate nutrient utilization in humans play an important role in fungi, especially when cells must distinguish between preferred and nonpreferred nutrients. This project will characterize conserved genes, including three highly conserved kinases, that play a role in distinguishing between available nutrients in eukaryotic microbes. An innovative aspect of this project is using powerful genomic tools, including high-throughput functional genomics and multi-omics, in understudied eukaryotic microbe model organisms with substantial nutrient utilization repertoires. Working in these two distantly related organisms will identify conserved genes that may be important for nutrient sensing throughout eukaryotic species and serve as novel targets to treat metabolic diseases in humans. Conversely, regulatory mechanisms specific to one species may serve as therapeutic targets to mitigate deaths from fungal disease.