Transcriptional control of connectivity in the visceral nervous system. – PanPhox2

Our project aims at understanding the formation of the visceral nervous system, i.e. a set of neural circuits that control digestion, blood circulation, and many aspects of breathing. The angle of attack is the central role played in the differentiation of most visceral neurons by a single, dedicated, transcription factor, the homeodomain protein Phox2b. This striking situation leads us to formulate two hypotheses: 1) All visceral neurons share a common “pan-visceral” genetic program downstream of their common transcriptional determinant; 2) This program might, at least in part, underlie the most obvious common property of visceral neurons, i.e. their projections to other visceral neurons or the viscera themselves. Two types of experiments are proposed to validate or invalidate these hypotheses. 1) An exploration of Phox2b’s capacity to impose axonal projections using a gain-of-function approach based on an ad-hoc transgenic tool: Phox2b will be ectopically expressed in an open-ended series of cells types, by combining a transgene which expressed it conditionally from a ubiquitous promoter with a series of Cre alleles . 2) An unbiased search for genes expressed by all visceral neurons and specific to them by a multiplex transcriptomic approach: three or more Phox2b+ cell types will be sorted from embryos where GFP is switched on cells that express Phox2b and their RNA will be deep-sequenced and compared, as well as with one or several Phox2b— cell types. In that way we hope to discover the molecular signature of a neuronal “supertype” the visceral neuron, and in it, potentially clues to the connectivity of the system. A third goal, making use of the tools developed for the first one, will be to explore the functional meaning of the secondary downregulation of developmental transcription factors, using Phox2b as a model.