C3: Trauma-induced signals promoting osteoblast plasticity and bone regeneration in the zebrafish fin
PI: G. Weidinger
In comparison to mammals, many lower vertebrates display highly elevated capacity for musculoskeletal regeneration, including the ability to fully restore amputated appendages. Identification of the molecular mechanisms linking trauma and initiation of a pro-regenerative programme in these organisms will help in defining why mammals regenerate less well and thus aid in development of regenerative therapies. Zebrafish robustly and completely regenerate their caudal fin including all bony elements after amputation. This system is uniquely suited to study the molecular mechanisms of vertebrate regeneration, since it combines high regenerative capacity, well-developed tools for functional genetic manipulations and the ability to perform medium- to large scale unbiased in vivo screens. We have previously identified dedifferentiation of mature osteoblasts to lineage-restricted proliferative progenitor cells as the earliest known regenerative cellular process induced by amputation trauma. These dedifferentiated progenitors then migrate to form the regeneration blastema, a population of cells thought to contain the cells and patterning information necessary to completely restore an amputated appendage. Bone in the fish fin thus regenerates from mature osteoblasts by a unique cellular mechanism of dedifferentiation. Therefore, regeneration is one of very few contexts in which cellular plasticity - the reversal of the differentiated state - occurs in vivo. In this project, we aim to identify molecular signals regulating osteoblast dedifferentiation and thus early trauma-induced regenerative responses. We expect that the identification of molecular regulators of osteoblast dedifferentiation will allow important insights into the regulation of cellular plasticity. In addition, since dedifferentiation is an early readout of a pro-regenerative response to trauma, our study should also identify conserved trauma-induced signals that act in other systems as well, including mammals, in particular in bone repair. Finally, since osteoblast dedifferentiation might represent a reversal of a molecular cascade similarly used in osteoblast differentiation, our project could also identify novel regulators of osteoblast differentiation. Using live transgenic reporters of the osteoblast differentiation status allows us to study the molecular regulation of this process in vivo. We will test the role of candidate signals involved in trauma-response in other systems, but will also perform an unbiased medium-throughput screen using a library of small molecules with characterised targets. Furthermore, we will use transcriptional profiling to identify a molecular signature associated with dedifferentiation. We will then study select pathways identified in the three approaches using in vivo loss- and gain-of-function approaches. Finally, we will ask whether signals identified in this screen also play a role in mammalian osteoblast differentiation and fracture repair.