Grafting of Apical Ridge and Polarizing Region
The apical ectodermal ridge (AER; also known as the apical ridge) and the zone of polarizing activity (ZPA; also known as the polarizing region) are two major signaling regions in developing vertebrate limbs. Limbs arise as small buds of undifferentiated mesenchyme cells encased in ectoderm. The apical ridge and the polarizing region were first identified in limb buds of chick embryos, and functions of these regions were explored by traditional “cut and paste” experiments by Saunders (reviewed in ref. 1). Similar signaling regions are also found in embryonic limb buds of other vertebrate species, including mice, rats, snapping turtles, and humans (2). Signals from apical ridge and polarizing region act together with signal(s) from the ectoderm in a region of undifferen-tiated cells called the progress zone (3). The progress zone is found at the tip of the bud as it grows out and is maintained by the apical ridge. As cells leave the progress zone, they lay down the...
KeywordsSonic Hedgehog Polarize Activity Apical Ectodermal Ridge Additional Digit Cold Slab
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