C3: Trauma-induced signals regulating osteoblast plasticity and migration during zebrafish regeneration
PI: G. Weidinger
In response to trauma, zebrafish display highly elevated regenerative abilities compared to mammals. We have previously shown that zebrafish employ an intriguing cellular mechanism to regenerate bone. Following traumatic injury of the tail fin, osteoblasts dedifferentiate, that is they lose markers of the differentiated state, re-enter the cell cycle and provide a progenitor population for new bone formation. We aim to understand the molecular mechanisms underlying this fascinating occurrence of cellular plasticity. In the first funding period, we took an unbiased approach towards identification of signals regulating osteoblast dedifferentiation by performing a high-throughput systematic search for small molecules that affect this process in vivo. We have successfully screened more than 1,500 drugs in more than 18,000 fish. This has resulted in several interesting hits targeting a variety of different cellular targets and signaling pathways, some of which we plan to further explore in the second funding period. Of particular interest to us are EGF receptor signaling and DNA damage repair pathways. One pathway uncovered by the screen, which we have already studied in detail in the first funding period, is NF-κB signaling, which surprisingly needs to be downregulated for osteoblast dedifferentiation to occur. We could show that NF-κB signaling acts cell autonomously in osteoblasts to inhibit dedifferentiation; in the second function period we aim to uncover the molecular mechanism through which the pathway does so. In the first funding period, we have also made great strides towards a better understanding of other cellular responses of zebrafish osteoblasts to trauma beyond dedifferentiation. In particular, by establishing high-resolution whole-fin imaging techniques we were able to show that osteoblasts radically alter their morphology and assume a migratory phenotype. Thus, in the second funding period, we plan to take advantage of the zebrafish fin regeneration model to uncover mechanisms of trauma-induced osteoblast motility and migration in vivo.