Hox genes in the development of respiratory circuits

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7. Project summary/ Abstract Breathing is a vital motor behavior that relies on diaphragm muscle contractions in mammals. The frequency and amplitude of breathing movements is controlled by neural networks residing in the brainstem and spinal cord. Degeneration of these networks leads to respiratory disorders, such as central sleep apneas, and, eventually, respiratory failure. My long term goal is to uncover the basic principles underlying respiratory circuit assembly so that we can begin to consider alternative treatment methods for respiratory dysfunction. A conundrum in the study of respiratory neural networks is that while significant progress has been made in defining the rhythmogenic circuits in the brain stem, the developmental origins, molecular identity and connectivity of spinal cord respiratory neurons remain unknown. Overall, the proposed research aims to define the genetic and molecular pathways that underlie spinal respiratory network assembly. We have recently demonstrated that the development of phrenic motor column (PMC) neurons in the cervical spinal cord, which innervate the diaphragm, requires the sustained activity of Hox5 genes. Mice lacking Hox5 genes in motor neurons (MNs) die of respiratory failure at birth and exhibit defects in multiple aspects of PMC identity, including clustering, axon guidance and diaphragm innervation. During the mentored part of this award, the role of Hox5 genes in PMC MNs will be further explored. Differential gene expression analysis will be carried out in order to identify genes acting downstream of Hox5 proteins to regulate distinct aspects of PMC development (Aim 1). Additionally, transsynaptic virus-based tracing approaches will be implored to examine how Hox5 removal from MNs affects the establishment of premotor inputs to the PMC (Aim 2). During the independent phase of the award, the role of Hox genes and their downstream targets in spinal cord respiratory interneuron development and connectivity will be examined (Aim 3). Addressing this question will rely heavily on genetic approaches, transsynaptic circuit labeling techniques and physiological respiratory assays, in which expertise will be acquired during the K99 phase. The mentored part of the research will be performed at the Dasen and Fishell labs at NYU Medical Center, an outstanding research environment that will provide all the equipment and facilities required for the proposed experiments. In addition, Dr. Kinkead at Laval University will act as a consultant and will provide training in the technique of plethysmography. I have assembled a committee who will oversee my progress and provide technical and intellectual input during the mentored part of the award. My previous experience in molecular neuroscience, in combination with a rigorous training plan, will ensure the successful completion of the proposed research aims, while the career development activities during the K99 phase of the award will facilitate a smooth transition to an independent position.