Photoreversal of Abnormal Morphogenesis in Sea‐urchin Embryos Caused by Uv‐irradiation

Morphological abnormalities induced by UV‐irradiation of 8‐ or 16‐cell‐stage embryos of the sea‐urchin, Hemicentrotus pulchenimus, and their photoreversal were studied. UV‐irradiation of the animal hemisphere of embryos caused the formation of exogastrulae, while that of the vegetal hemisphere caused the formation of permanent blastulae. These UV‐induced morphological abnormalities were photoreversed when the UV‐irradiated embryos were subsequently illuminated with visible light, so that the UV‐irradiated embryos developed into normal pluteus‐larvae. When UV‐irradiated embryos were illuminated with visible light up to the onset of the DNA‐synthesis phase of the following cell cycle, the UV‐induced morphological abnormalities were photoreversed almost completely. The effectiveness of an exposure to visible light declined thereafter and was subsequently completely lost.