Genetic Control of Respiratory Motor Circuit Development, Connectivity and Maintenance

Project Summary/Abstract Breathing is a vital motor behavior which is controlled by neural circuits within the brainstem and spinal cord. Degeneration of these circuits leads to respiratory disorders, such as central sleep apneas, and, eventually, respiratory failure. In mammals, contraction of the diaphragm muscle is essential for driving airflow into the lungs during inspiration. At the core of respiratory circuits are Dbx1-derived interneurons in the brainstem, which generate the rhythm and pattern of breathing, and phrenic motor neurons (MNs) in the spinal cord, which provide the final motor output that drives diaphragm muscle contractions during inspiration. Despite their critical function, the principles that dictate how respiratory circuits assemble are largely unknown. We have found that sustained activity of Hox5 transcription factors is required in both phrenic MNs and Dbx1- derived brainstem neurons to generate normal breathing behaviors and robust respiratory motor output. In this proposal we will investigate the function of Hox5 genes in determining respiratory neuron specification, connectivity and maintenance. In Aim 1 we will define how Hox5 gene expression underlies the specification and connectivity of Dbx1-derived brainstem neurons at distinct time points. In Aim 2 we will test the hypothesis that sustained, cell-autonomous Hox5-dependent programs drive and maintain phrenic MN connectivity. In Aim 3 we will utilize a novel mouse model to define the molecular mechanisms that control the specification and development of brainstem respiratory neurons. We have developed an integrative methodology combining genetic models, next-generation sequencing approaches, retrograde viral tracing, and electrophysiology to address these questions in vivo. The overarching goal of this proposal is to uncover the basic principles underlying respiratory circuit assembly so that we can begin to consider alternative treatment methods for respiratory dysfunction.