Tissue specific expression alternatively spliced murine PECAM-1 isoforms

PECAM-1 (CD31) is a cell adhesion molecule that is highly expressed at the sites of endothelial cell-cell contact and at lower levels on the surface o f platelets and leukocytes, It is a member of the immunoglobulin gene super family and undergoes alternative splicing to generate several isoforms that differ only in their cytoplasmic domains. The tissue distribution of the e xpression of different PECAM-1 isoforms has not been previously defined. We have examined PECAM-1 expression in various mouse tissues and endothelial cells. PECAM-1 mRNA was highly expressed in lung, heart, and kidney, and to a lower extent in brain and liver, Most endothelial cells in culture expre ssed high levels of PECAM-1 mRNA; however, normal mouse brain endothelial c ells rapidly lost PECAM-1 expression in culture. To examine the tissue dist ribution of PECAM-1 isoform expression, RT/PCR was performed on the RNA iso lated from various mouse tissues and mouse endothelial cells. Cloning and s equencing of the cDNA products indicated that most tissues and endothelial cells expressed several PECAM-1 isoforms at different frequencies. The PECA M-1 isoform that lacks exons 14 and 15 was most frequently detected in all cases. A novel PECAM-1 isoform that lacks exons 12 and 14 was detected in b rain. An antibody to the extracellular domain of PECAM-1 reacted with two m ajor bands, at 130 kDa and 110-120 kDa, in lysates prepared from endothelia l cells or kidneys at different stages of development. An antibody prepared against PECAM-1 exon 14, which reacts only with cytoplasmic domain of PECA M-1 isoforms that contain exon 14, failed to react with the major lower mol ecular weight form of PECAM-1 in these lysates. Therefore, PECAM-1 isoforms that lack exon 14 are expressed in endothelial cells and tissues in develo pmentally regulated fashion. These results illustrate that multiple PECAM-1 isoforms are expressed in various mouse tissues and endothelial cells. Und erstanding the distribution of PECAM-1 isoforms, and the identity of intrac ellular proteins with which they may interact, will help to elucidate the r ole of PECAM-1 in endothelial cell-cell interactions and morphogenesis, Dev Dyn 1999;214:44-54. (C) 1999 Wiley-Liss, Inc.