While mammals have a limited capacity to repair bone defects, zebrafish can completely regenerate amputated bony structures of their fins. Fin regeneration is dependent on formation of a blastema, a progenitor cell pool accumulating at the amputation plane. It is unclear which cells the blastema is derived from, whether it forms by dedifferentiation of mature cells, and whether blastema cells are multipotent. We show that mature osteoblasts dedifferentiate and form part of the blastema. Osteoblasts downregulate expression of intermediate and late bone differentiation markers and induce genes expressed by bone progenitors. Dedifferentiated osteoblasts proliferate in a FGF-dependent manner and migrate to form part of the blastema. Genetic fate mapping shows that osteoblasts only give rise to osteoblasts in the regenerate, indicating that dedifferentiation is not associated with the attainment of multipotency. Thus, bone can regenerate from mature osteoblasts via dedifferentiation, a finding with potential implications for human bone repair.
A 10-year-old boy with bilateral colobomatous cavitary disc anomalies presented with a 3-month history of vision loss in his right eye. MRI of the head and orbit revealed bilateral tubular cystic enlargement of the optic nerve/optic sheath complex with thickening of the optic nerves without inflammation or neoplasm, suggestive of bilateral optic nerve meningocele. An optic nerve sheath fenestration was performed OD, and he experienced an improvement and stabilization of vision in his right eye during a 1-year follow-up period. The authors recommend that surgical decompression, particularly optic nerve sheath fenestration, should be considered in cases with progressive vision loss due to optic nerve meningocele.
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