Bone Abstracts

Purpose: The aim of this research was to develop an in vivo platform for conveniently examining the potential of various factors to augment chondral bone regeneration. For this purpose, we have established a de novo partial tail amputation model in adult zebrafish, which includes the resection of cartilage-template based bones from the endoskeletal caudal complex. Endoskeletal amputations were rarely studied, as opposed to those of the distal caudal fin rays, a well-established model of membranous bone regeneration.

Methods: Amputations initiated proximally at the distal 2–3 mm of the dorsal part of the tail that has scales and musculature, and then proceeded distally towards the dorsal fin rays. Fish skeletons were vitally labelled with two Ca²⁺ -binding chromophores: calcein 2 days before amputation, and 20 days later, alizarin red. To overcome the potential artifacts of autofluorescence, and the spectral overlap between both chromophores, we employed spectral imaging coupled with image analysis using the linear unmixing algorithm.

Results: After the amputations fish were vital, and normal activities were not compromised. The labelling method, which was validated in the distal caudal fin model, exhibited newly formed bone, mainly some broadening at the tip of the stump in neural spines, while hypurals did not regenerate. None of the caudal complex bones regrew to form a structure similar to the original one, even 7 months post amputation.

Conclusions: We suggest that neural spines undergo a progressive widening at the tip of the stump after amputation, which resembles hypertrophic nonunion fracture in humans, while hypurals do not seem to regenerate. Thus, our model is appropriate for the investigation of potential therapeutic factors for augmenting chondral bone regeneration, either for the induction of de-novo regeneration or for examination of treatments for abnormal regrowth; both of major importance for clinical conditions and aspects of regenerative medicine.