Endo T et al. (2007), Brain regeneration in anuran amphibians.

XB-ART-35431

Dev Growth Differ 2007 Feb 01;492:121-9. doi: 10.1111/j.1440-169X.2007.00914.x.

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Brain regeneration in anuran amphibians.

Endo T , Yoshino J , Kado K , Tochinai S .

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Urodele amphibians are highly regenerative animals. After partial removal of the brain in urodeles, ependymal cells around the wound surface proliferate, differentiate into neurons and glias and finally regenerate the lost tissue. In contrast to urodeles, this type of brain regeneration is restricted only to the larval stages in anuran amphibians (frogs). In adult frogs, whereas ependymal cells proliferate in response to brain injury, they cannot migrate and close the wound surface, resulting in the failure of regeneration. Therefore frogs, in particular Xenopus, provide us with at least two modes to study brain regeneration. One is to study normal regeneration by using regenerative larvae. In this type of study, the requirement of reconnection between a regenerating brain and sensory neurons was demonstrated. Functional restoration of a regenerated telencephalon was also easily evaluated because Xenopus shows simple responses to the stimulus of a food odor. The other mode is to compare regenerative larvae and non-regenerative adults. By using this mode, it is suggested that there are regeneration-competent cells even in the non-regenerative adult brain, and that immobility of those cells might cause the failure of regeneration. Here we review studies that have led to these conclusions.

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Species referenced: Xenopus laevis
Genes referenced: cer1

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	Fig. 1. Telencephalon (cerebrum and olfactory bulb) regeneration in Xenopus larvae and froglets. (a) Illustration of the brain in Xenopus. The anterior half of the telencephalon was removed. The broken line indicates the amputation site. cer; cerebrum, ob; olfactory bulb. (b–g) Horizontal sections of the telencephalon in larvae (b–d) and froglets (e–g). (b, e) Intact; (c, f) immediately after amputation; (d, f) 30 days after amputation. Scale bars, 300 μm.
	Fig. 2. Optic tectum regeneration in Xenopus larvae and froglets. (a) Illustration of the brain in Xenopus. mes; mesencephalon. (b) A 3-D image of the anterior half of the mesencephalon as seen from the posterior. The right optic tectum was removed from the whole mesencephalon. (c–g) Crosssections of the mesencephalon in larvae (c–e) and froglets (f, g). Immediately (c, f), 4 days (d) and 30 days (e, g) after tissue removal. Scale bar, 300 μm.
	Fig. 3. Schematic illustration of regenerative differences between larval and adult brain tissues in Xenopus. (b) After brain injury, periventricular cells in the vicinity of the wound migrate and close the wound in larvae, but not in adults. (c) The rate of cell proliferation increases around the regeneration site and the regenerating tissue thickens in larvae. A temporal increase in cell proliferation is also observed in adult brains. (d) Regeneration of a functional brain is completed in about a month in larvae. Conversely, the wound site is never closed and no regeneration occurs in adults.