Premature specification of the retina in embryonic Xenopus eyes treated with ionophore X537A.

Eyes excised from Xenopus embryos at stages 24 to 25 were cultured for 4 to 6 hours in a medium containing the ionophore X537A or in a control medium. The eyes were implanted either upside down or normally in host embryos at stages 28 to 30, and their retinotectal projections were mapped after metamorphosis. Treatment with X537A prevented realignment of retinal axes in eyes implanted into hosts that were capable of producing retinal axial alignment in all control eyes.