Protocadherin 12 (VE-cadherin 2) is expressed in endothelial, trophoblast, and mesangial cells.

Protocadherin 12 protein (PCDH12, VE-cadherin 2) is a cell adhesion molecule that has been isolated from endothelial cells. Here, we have used Northern and Western blots, immunohistology, and flow cytometry to examine the distribution of PCDH12 in mouse tissues. It is an N-glycosylated protein of 150-kDa mass. In the endothelium, PCDH12 immunoreactivity was variable and dependent upon the vascular bed. In both the embryo and embryonic stem cell differentiation system, signals were localized in vasculogenic rather than angiogenic endothelium. In addition, the protein was strongly expressed in a subset of invasive cells of the placenta, which were identified as glycogen-rich trophoblasts. In adult mice, strong PCDH12 signals were observed in mesangial cells of kidney glomeruli whereas expression was not detected in other types of perivascular cells. As opposed to most protocadherins, PCDH12 is not expressed in early embryonic (day 12.5) and adult brains. As a first approach to obtain insight into PCDH12 function, we produced transgenic mice deficient in PCDH12, which were viable and fertile. They did not display any obvious histomorphological defects. We conclude that PCDH12 has a unique expression pattern and that its deficiency does not lead to conspicuous abnormalities. Moreover, PCDH12 is the first specific marker for both glycogen-rich trophoblasts and mesangial cells.