A common protocadherin tail: Multiple protocadherins share the same sequence in their cytoplasmic domains and are expressed in different regions of brain

To study the diversity of protocadherins, a rat brain cDNA library was scre ened using a cDNA for the cytoplasmic domain of human protocadherin Pcdh2 a s a probe. The resultant clones contained three different types. One type c orresponds to rat Pcdh2; the other two types are distinct from Pcdh2 but co ntain the same sequence in their cytoplasmic domains and part of the 3' fla nking sequence. To clarify the structure of the proteins defined by the new clones, a putative entire coding sequence corresponding to one of the clon es was determined. The overall structure is essentially the same as Pcdh2, indicating that the proteins defined by this clone, and probably by other c lones, belong to the protocadherin family. Two PCR experiments and an RNase protection assay showed the existence of the corresponding mRNAs in rat br ain preparations. Human and mouse cDNA clones with the same sequence proper ties were also isolated. Taken together, these results indicate that the cl ones are not cloning artifacts and that corresponding mRNAs are actually ex pressed in brains of various species. The results of in situ hybridization showed that the mRNAs corresponding to these clones were expressed in diffe rent regions in brain. Since protocadherins encoded by these mRNAs are like ly to have different specificity in their interaction and share a common ac tivity at their cytoplasmic domains, these protocadherins may provide a mol ecular basis, in part, to support the complex cell-cell interaction in brai n.