LIVE IMAGING OF BONE REGENERATION IN ZEBRAFISH

Abstract Mammalian bone has the capacity throughout life to regenerate in response to fracture injury. However, there is a ceiling for this regenerative potential, with hurdles to regeneration after a major trauma like limb amputation. This has a significant socioeconomic impact, as it is estimated that at least one in two Americans over age 50 is expected to have or be at risk of bone disease, and every year an estimated 1.5 million individuals suffer a fracture due to bone disease. Recently, we have developed imaging methods to study how osteoblasts drive bone regeneration in zebrafish, which display robust regeneration after major injury to bony structures like their fins, scales, and jaws. Our strategy is to exploit this regenerative capacity, new imaging platforms we have created, and the molecular genetic approaches available in zebrafish to improve our ability to understand and manipulate the regenerative capacity of bone. The goal of this renewal proposal is to identify mechanisms that encode complex biological patterns like waves and gradients during bone regeneration. Our experiments will test the hypothesis that regeneration of skeletal structure is templated by complex biological patterns in signaling pathway activity and polarized gene expression. 1) We will identify positive and negative signaling influences on traveling Erk waves that mediate osteoblast behaviors during zebrafish scale regeneration, based on assessment of a panel of mutant animals. 2) We will test the extent to which patterns of secreted Fgf ligand control Erk signaling gradients and determine the extent of osteoblast cycling and skeletal growth during regeneration of amputated fins. 3) We will use transcriptome and chromatin profiling, as well as imaging approaches, to identify determinants of positional memory along the anteroposterior axis of regenerating pectoral fins. These experiments will define a novel quantitative framework for understanding how osteoblast behaviors orchestrate bone regeneration.