Genetic and extrinsic mechanisms governing early enteric nervous system development

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Resident between the muscle walls of the entire gastrointestinal (GI) tract, the enteric nervous system (ENS) consists of a series of interconnected neurons and glia, numbered in the hundreds of millions. The ENS controls essential gut functions, such as peristalsis, water balance and intestinal barrier homeostasis. The ENS is derived from enteric neural progenitors (ENPs) that migrate into the developing gut tube during embryogenesis and differentiate into enteric neurons or glia. Disruption in ENS formation results in the congenital condition Hirschsprung disease (HSCR), in which variable regions of the GI lack ENS—the most common form of HSCR presents along the distal colon, also known as colonic aganglionosis. The underlying cellular mechanisms that ENPs utilize to migrate into and spatially position along the gut tube, as well as genetic programs they execute to differentiate into enteric neurons have not been well studied in vivo, therefore limiting our knowledge of how the ENS manifests. The overall goal is to expand foundational knowledge of the genes utilized to execute the complex mechanisms necessary for ENS formation, with an eye for informing downstream translational therapeutic studies. In this proposal, we utilize zebrafish embryos due to their genetic conservation with humans, the ease of viewing their external development and for their optical transparency. Building off of single-cell transcriptomic data sets generated from ENP cells collected during their early neurogenesis along the gut tube, Aim 1 will examine a hypothesis that the spatial arrangement of newly uncovered ENP transcriptional subpopulations predict future enteric neuron placement and terminal differentiation along the gut tube. In agreement with and extending observations in mammalian models, we have recently discovered that Retinoic Acid (RA) signaling is critical globally during early steps of zebrafish ENS development; however, how RA signaling autonomously influences ENS ontogenesis in vivo is not well understood in any system to date. Aim 2 will investigate a hypothesis that the RA pathway autonomously controls ENP differentiation states and migration patterns along the gut tube using cutting edge single-cell transcriptomics, optogenetics and in vivo imaging. We will also test a mechanistic model in Aim 2 that candidate transcription factors function intrinsically downstream of RA in ENPs to govern ENS formation, thereby expanding our understanding of the ENS gene regulatory network. Aim 3 will use genetic modulation of the cell cycle, quantitative in vivo imaging and cell tracking test a cellular mechanistic model that ENPs couple proliferation with migration to dictate proper enteric neuron patterning in the gut downstream of the RA pathway. The results of these aims will significantly increase our knowledge of the genetic, molecular and cellular underpinnings of ENP development and early ENS creation and they will provide a new mechanistic framework for studying these developmentally important cells in vivo.