Discovering Mechanisms Underlying the Formation of a Straight Body Axis

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PROJECT SUMMARY/ ABSTRACT: How the linear head-to-tail body axis forms during development and is then maintained during growth is little understood. Defects in axial straightening — the morphogenetic process through which a linear axis forms — result in structural birth defects and spinal curves such as scoliosis. In this proposal, we use the tractable zebrafish system to discover principles underlying the formation and maintenance of a linear body axis. Zebrafish embryos are initially curved ventrally around a ball of yolk but, by around 32 hours post fertilization, the embryonic axis has straightened to produce an autonomously swimming larva. Axial straightening requires motile cilia, which beat and generate cerebrospinal fluid (CSF) flow in the central canal. Abnormalities in cilia beating result in a failure of straightening, with larvae maintaining ventral curves. Using a novel double mutant line, in Aim 1 we determine mechanisms underlying the function of neuropeptides Urp1 and Urp1 downstream of cilia motility. This will rigorously test the model that axial straightening depends on Urotensin peptides as well as establish new animal models for scoliosis. Next, we assess how morphogenetic movements that straighten the axis stop precisely when a straight axis is generated. In pkd2 mutant embryos, this stopping process fails, leading to abnormal dorsal curves. In Aims 2 and 3, I will determine the mechanisms through which Pkd2 functions in controlling axial linearity. In Aim 2, I will test the hypothesis that Pkd2 regulates cilia-independent processes that control the dorsal muscle contractions which supply the force for morphogenetic body movements. In Aim 3, I will test the role of the notochord, a stiff rod down the center of the body, in maintaining straightness once it is generated, and the potential role of Pkd2 in this tissue. Overall, my work will discover new principles of how multiple tissues — the motile cilia/CSF/neuronal interface within the central canal, dorsal somitic muscle, and the notochord — coordinate to generate a linear body axis. This work will have implications for understanding how the correct anatomy of an organism is generated through self-organizing processes, something important for understanding the origin of structural birth defects and for regenerative medicine. My work will use a range of innovative techniques and provide me with a rigorous training in cell and developmental biology.