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The Role of Retinoic Acid in Planarian Regeneration

Planarians serve as a good model organism for studying regeneration. They regenerate by utilizing a subset of cells called neoblasts. Neoblasts are recruited to the site of injury to form the blastema. Retinoic acid (RA) is a small Vitamin A derivative. It is important in several regenerating animals. This study looks specifically at its role in planarian regeneration. To begin, we examined at the expression pattern of Raldh-2, the rate-limiting enzyme in RA metabolism. We found it expressed distinctly around the digestive tract. Using the drug DEAB, known to inhibit Raldh-2, we eliminated the production of RA acid and studied the effect on regeneration. We found that regeneration was disrupted in DEAB-treated animals. The drug exhibited an asymmetric affect, affecting the anterior portions more. In fragmented animals, the anterior-facing blastemas were malformed. Additionally, the pre-pharyngeal fragments died at a higher rate than the post-pharyngeal.