We have tried to describe these things in every day language as much as possible, so that anyone with patience can understand what we are talking about. Again, please take your time and enjoy the page. Retinoids belong to a family of biochemicals that include vitamin A, and are extremely important in embryonic development. In excess, retinoids can be a dangerous teratogen, causing serious birth defects in humans. Quite a bit is known about the biochemistry of retinoids, especially vitamin A, so it makes a very good story.
Retinoic acid is known to be able to activate certain patterning genes in the limb bud.
Not surprisingly, adding abnormal amounts of RA to a developing limb bud can cause a disruption of normal development. So retinoic acid does NOT convert posterior cells into anterior cells. These are very important results which will help us evaluate the possible role of retinoids in deformed amphibians. If developing limb buds are treated with RA it prevents the limb bud from growing at all. RA can also cause extra limbs but only if the limb was regenerating when it was exposed to the chemical.