Untreated retinal detachment inevitably causes blindness in humans. However, birds, fish and urodele amphibians are luckier – they can regenerate their retinas. On p. 4607, Spence and co-workers investigate this process in chick embryos. They describe how two modes of retinal regeneration – transdifferentiation of retina pigmented epithelium (RPE) and activation of stem/progenitor cells in the ciliary body and ciliary marginal zone (CB/CMZ) – are both stimulated by Fibroblast growth factor 2 (Fgf2). In addition, they show that ectopic expression of Sonic hedgehog (Shh) stimulates regeneration from the CB/CMZ in the absence of Fgf2, and that Shh-induced regeneration requires Fgf signalling. By contrast, ectopic Shh expression inhibits retinal regeneration via RPE transdifferentiation, indicating that Shh is involved in RPE maintenance. Spence et al. conclude that the hedgehog pathway is an important modulator of both types of retinal regeneration.
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