Morphogenetic action of the subcommissural organ on tail regeneration inXenopus larvae.

In an earlier paper (Hauser, 1969) it was suggested that the subcommissural organ (SCO) in the roof of the diencephalon might control normal straight regeneration after amputation of the tail tip inXenopus larvae, by means of Reissner's fibre (RF) its secretory product in the central canal of the spinal cord. This hypothesis has been experimentally tested, with results that appear to confirm it, as follows: 1. Elective destruction of the SCO caused characteristically disturbed tail regeneration, while other brain lesions did not affect normal tail regeneration. 2. RF degenerated within 24 hrs in the caudal neural tube after it had been severed at the base of the tail. In most cases the separated parts of the neural tube resumed contact within less than 4 days in such a way as to allow RF re-entry into the central canal of the caudal piece, but occasionally reconstitution of RF was prevented by complete or partial obstruction of the central canal. Histological examination revealed that whether or not the tail regenerated normally depended entirely upon the reconstitution of RF, and not on the restoration of central canal continuity as such. The implications of these results, and of similar results recently obtained by Rühle (1971), for the understanding of SCO function are discussed.