Interpreting Bone Morphogenetic Protein Gradients in Vertebrate Development

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Project Summary/Abstract Animal development consists of complex cell coordination and rearrangement via intercellular communications. It is not well understood how progenitor cells interpret neighbor cell signals that impact cell fate decisions. One critical signaling element in animal development is morphogen signaling. Bone morphogenetic protein (BMP) acts as a morphogen to pattern the dorsoventral (DV) axis during vertebrate development, where BMP concentration gradients correlate with different cell identities. To study the mechanism in which progenitors interpret BMP gradients, I look to zebrafish development. Zebrafish are transparent during embryonic and larval stages, facilitating high resolution microscopy of cell fate change and migration patterns. Zebrafish share more than 70% of their genes with humans, making them excellent models for human development and disease research. Using zebrafish embryos, I will manipulate BMP concentration, progenitor cell location, and BMP signal duration within mesodermal progenitors and determine the morphogenetic outcome. In Aim 1 of this project, I will investigate the mechanism in which BMP signal coordinates its migration and cell fate gene expression that results in its characteristic morphogenetic output. With DV BMP morphogenetic signaling, cells may be positioned in embryonic domains where the microenvironment affects a binary fate switch. To answer my question, I will be using transgenic embryos to conditionally overexpress ectopic BMP signal. Transplanting transgenic cells into wildtype (WT) embryos prior to gastrulation stages will allow for the analysis of transgenic cell fate decisions within the WT environment. I will analyze time lapses of developing embryos containing these transgenic cells using spinning disk confocal microscopy. Cell fates will be genetically assessed using in situ hybridization and fate-specific fluorescent probes before, during and after gastrulation. In Aim 2, I will be determining the role that BMP signal duration has on cell fate decisions. I will be utilizing the Auxin Inducible Degron (AID) system to create specific durations of BMP signaling and BMP target gene expression in order to determine how signal duration impacts fate. Because a direct BMP target protein inhibits the transcription of cell fate specific transcription factors, I hypothesize that the duration of BMP signaling would change the amount of time that this target gene is present, allowing cell fate genes to bind when they normally would not be able to, thus altering cell fates. The combined use of cell autonomous reporter fish lines, transplantation, gene expression analysis, transgenic fish utilizing the AID system, and spinning disk confocal microscopy will allow me to test my hypotheses.