A Hidden Retinal Regenerative Capacity from the C Ciliary Margin is Reactivated In Vitro, that is Accompanied by Down-regulation of Butyrylcholinesterase

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Abstract
The chicken retina has a capacity to regenerate in vivo, which is restricted up to embryonic day 4 (E4). Here we test the proliferative patterns of dissociated chicken cells from the centre retina or the ciliary margin, including pigmented cells, after their transfer into rotation culture. For central cells in culture, the uptake of [3H]thymidine after a short initial rise decreases similarly to their in ovo counterparts. In contrast, marginal cells that have been shown to regenerate up to E9 into retinotypic stratospheroids re-enter a novel and long-lasting phase of in vitro cell division. We have shown previously that cell types of all nuclear layers are produced. Both observations taken together indicate a pronounced self-renewal of multipotent stem cells. Molecularly, the enzyme butyrylcholinesterase, which in other systems has been shown to mark transitory neuronal cells between proliferation and differentiation, is strongly expressed at the ciliary margin over most of the embryonic period. After these cells are transferred into rotation culture, butyrylcholinesterase is down-regulated. Concomitantly, the neuronal differentiation marker acetylcholinesterase increases. We conclude that the regenerative capacity of the chick retina is not lost at E4, but rather remains hidden in the chicken ciliary margin, since it can be reactivated in vitro at least up to E9. We suggest that butyrylcholinesterase may be linked to the regulation of stem cell activity.