Retinoic acid is a known morphogen in regulating animal growth and development. Planaria are a key model system for regeneration and their eyes are a morphological marker of anterior differentiation. We explored the requirement for retinoic acid signaling in the regeneration of body parts in the planaria S. mediterranea using an inhibitor of retinoic acid synthesis, diethylaminobenzaldehyde (DEAB). Whole planaria, soaked in DEAB for three days prior to and five days following amputation, produced trunk and tail fragments with defective anterior regeneration. Following regeneration, up to 80% of posterior fragments developed abnormal eyes. The abnormalities included animals without eyes, with only a single eye, with one enlarged eye, or two eyes of different sizes. Eyes were considered to be functional because animals responded to blue laser light with turning behavior. No abnormalities in eye regeneration were observed in side by side vehicle controls. These results suggest that retinoic acid is necessary for normal eye regeneration following injury and supports a previously undocumented signaling role in planaria eye development.

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