The Xenopus laevis tail-forming region

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Abstract
A fate map is produced for the Xenopus tail-forming region at the neurula stage by orthotopic grafting of tissue labelled with fluorescein-dextran amine. It is shown that the axial tissues of the tail are derived from a rectangle 700 μm wide by 600 μm long, while the epidermis of the tail is drawn from a much larger area. The fate map shows that much of the final tail is not formed from the tail bud itself, but by a displacement of trunk axial tissue relative to the proctodaeum. A specification map is also produced by culturing parts of the tail-forming region in vitro or as grafts on a neutral site on host embryos. For the axial tissues this map is identical to the fate map, showing that the tail-forming region is embryologically mosaic. The prospective tail epidermis can, however, regulate defects. It is shown that previous claims of regeneration of the Xenopus tail bud are misleading. Removal of the tailforming region totally prevents tail development. Removal of the tail bud leads to a partial tail, formed by the normal process of displacement of trunk tissue relative to the proctodaeum. Even when only part of the tail bud is removed the tail is still truncated. This shows that there is no terminal regeneration of the tail at embryonic stages.