The monoclonal antibody 103-A1 recognizes mouse nectin-3. Nectin-3 is a 83 kDa type Itransmembrane glycoprotein. Nectin, originally isolated as poliovirus receptor-related protein (PRR), isa cell-cell adhesion molecule of the immunoglobulin supergene family. Nectins are calciumindependentimmunoglobulin-like cell-cell adhesion molecules consisting of four members, nectin 1-4.Nectins homophilically and heterophilically trans-interact to form a variety of cell-cell junctions,including cadherin-based adherens junctions in epithelial cells and fibroblasts in culture, synapticjunctions in neurons, and Sertoli cell-spermatid junctions in testis, in cooperation with, orindependently of, cadherins. Both nectin-2 and nectin-3 are ubiquitously expressed, whereas nectin-1is abundantly expressed in brain. Nectin-2 and -3 are expressed in cells where cadherin is notexpressed, such as blood cells and spermatids. All members of the nectin family have two or threesplice variants. For nectin-3, three isoforms exist: nectin-3α, -3β and -3g of which nectin-3α is thelargest. Nectin-3, also known as PRR3, is a transmembrane protein that is predominantly expressedin testis and placental tissues as well in many cell lines. Nectin interacts in vivo with both long andshort isoforms of afadin, an actin binding protein, at cadherin-based cell-cell adherence junctions invarious tissues and cell lines. Furthermore, the ectodomains of nectin-3 and CD155 (PoliovirusReceptor) have shown strong affinity to each other.Injection of antibody 103-A1 into lumen of seminiferous tubules leads to disruption of the actinfilaments in Sertoli cells at the Sertoli-maturing spermatid ectoplasmic specialization and exfoliation ofmaturing spermatids form the seminiferous epithelium.