In humans, healing broken bones is slow and painful, and lost limbs can never be regrown, yet some species have far more resilient skeletons. Zebrafish are able to entirely regenerate amputated fins, an impressive feat completed within only two weeks. Clusters of specialised skin cells split and move from the base to the tip of the fin to activate bone-producing stem cells, or osteoblasts, using a signalling molecule known as sonic hedgehog (Shh). Labelling the cells responding to Shh with green fluorescence in a developing tail fin (pictured) tracks the growing fin bones, or rays. Communication between skin cells and osteoblasts is critical to obtaining a skeleton with the appropriate pattern: when the Shh signalling pathway is blocked, fins develop incorrectly, with straight, unbranched rays. While not aiming to replicate the regenerative capacity of zebrafish in humans, understanding how Shh underpins it could inspire new ways to stimulate bone repair.
Written by Emmanuelle Briolat
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