MOLECULAR-CLONING OF RAT AND MOUSE MEMBRANE COFACTOR PROTEIN (MCP, CD46) - PREFERENTIAL EXPRESSION IN TESTIS AND CLOSE LINKAGE BETWEEN THE MOUSE MCP AND CR-2 GENES ON DISTAL CHROMOSOME-1

Human membrane cofactor protein (MCP, CD46) is widely distributed and is one of the plasma membrane complement inhibitors. We isolated cDNA clones encoding genetic homologues of human MCP from a rat testis cDNA library. Northern blot analysis indicated that rat MCP is preferentia lly expressed in testis, similar to what is found with guinea pig MCP. We identified several different cDNAs, which were presumably generate d by alternative splicing from a single-copy gene. The most prevalent isoform corresponded to the Ser/Thr/Pro-rich C type of human MCP. Mous e MCP cDNA was cloned by polymerase chain reaction based on the nucleo tide sequence of rat MCP. The deduced amino acid sequence showed 77.8% identity to rat MCP. Mouse MCP was also preferentially expressed in t estis. Unique expression in testis in rat and mouse as well as guinea pig suggests that MCPs in these species not only act as complement reg ulatory proteins but may also have more specialized functions in ferti lization or reproduction. Genetic mapping by linkage analysis indicate d that the mouse Mcp gene is located on distal chromosome 1, closely l inked to the complement receptor 2 (Cr2) gene.