Optogenetic dissection of Erk signal interpretation in early embryogenesis

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PROJECT SUMMARY/ABSTRACT Signaling pathways pattern cell fate choices in the developing embryo, but how do only a limited number of pathways control the complex events of development? Spatial signaling gradients as well as temporal signaling dynamics are known to be important for directing multiple fates with the same pathway, yet the mechanisms cells use to interpret these signaling events remains largely uncharacterized. One pathway which plays diverse roles throughout embryogenesis, wound healing, and cancer progression is the highly conserved extracellular signal-regulated kinase (Erk) signaling network. The early Drosophila embryo is a classic in vivo model of tissue patterning by Erk signaling: a spatial gradient of Erk signal at the poles specifies anterior and posterior structure and dictates endoderm versus ectoderm fate decisions. Although these patterns are well-defined, recent work in the Toettcher laboratory using an optogenetic tool to manipulate the Erk signal in vivo with exquisite spatial and temporal precision has revealed major open questions about the mechanisms by which Erk signals are interpreted. Here, I propose to define the mechanisms by which the Drosophila embryo interprets differences in Erk dose to create spatial patterns of gene expression and make decisions about cell fate. To address this question, I will use a combination of cutting-edge optogenetic tools, live-cell biosensors, genomic analysis, and classical genetic perturbations. In Aim 1, I will examine how spatial patterns of gene expression are robust to major corruption of the Erk gradient. In Aim 2, I will explore how only two transcription factors can control multiple distinct fates over a wide range of Erk signal strength. Altogether, using precision tools for manipulating signaling inputs and quantifying expression outputs, this proposal will reveal how Erk signals are measured and interpreted by downstream genes, addressing a fundamental question in developmental biology which will surely have relevance for other signaling pathways and cellular contexts for Erk signaling. Through this research and the accompanying training plan I will obtain exceptional training in optogenetics, advanced microscopy, and genomics, positioning me for an impactful career at the interface of cell and developmental biology.