Protocadherin 21 (PCDH21)

PCDH21 is a member of the cadherin superfamily of calcium-dependent cell-cell adhesion molecules. This non-classical cadherin appears to be exclusively expressed in the mitral and tufted cells in the main and accessory olfactory bulbs of the brain, suggesting a possible role in the formation and maintenance of neuronal networks. Alternatively spliced transcript variants encoding different isoform have been identified.

Protocadherins were discovered by Shintaro Suzuki's group, when they used PCR to find new members of the cadherin family. This prevalence in a wide range of species suggested that the fragments were part of an ancient cadherin and were thus termed "Protocadherins" as the "first cadherins".