Protocadherins comprise the largest group within the cadherin family of calcium-dependent cell-cell adhesion molecules. Protocadherin 12 (PCDH12) was initially identified through PCR screening of mouse heart microvascular endothelial cell RNA; further experiments revealed its mRNA to be strongly expressed in highly vascularized organs such as lung and kidney, in addition to glycogen-rich trophoblasts in the placenta. PCDH12-null mice are viable and fertile, but show reduced placental and embryonic sizes when compared to wild-type mice. Further studies showed significant expression changes in 2, 289 genes, including those involved in tissue morphogenesis, angiogenesis, cell-matrix adhesion and migration, immune response and chromatin remodeling.