MONDAY, Nov. 19 (HealthDay News) -- U.S. researchers say they've uncovered new clues on how embryonic cells regulate levels of retinoic acid, a derivative of vitamin A.

Retinoic acid plays a vital role in embryo development, acting as a signal between cells to control development of the brain, limbs and many other tissues. Human embryos that get too much or too little retinoic acid may develop birth defects, noted a team from the University of California, Irvine.

When humans consume vitamin A -- found in many foods, including carrots, broccoli and sweet potatoes -- the body converts it into retinoic acid.

"If you don't get enough vitamin A in your diet -- or if you get too much -- your body compensates for that. Our study helps explain how this regulation occurs," Thomas Schilling, associate professor of developmental and cell biology at UC Irvine, said in a prepared statement.

The UC Irvine team examined retinoic acid in zebrafish embryos, which are often used in genetic studies as models for human development. They found that if levels of retinoic acid become too high, an enzyme called cyp26a1 degrades the excess retinoic acid in order to restore normal levels. If levels are too low, proteins called fibroblast growth factors (FGFs) slow retinoic acid degradation.

"Those two things work together to keep the whole system adjusted to the right level. Retinoic acid induces its own degradation, and FGFs, also present in the embryo, have the opposite effect by inhibiting retinoic acid degradation," Schilling said.

The study is published in the Nov. 20 issue of the journal Public Library of Science Biology.

More information

MedlinePlus has more about vitamin A.

-- Robert Preidt

SOURCE: University of California, Irvine, news release, Nov. 19, 2007

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