MOLECULAR CHARACTERIZATION OF RAT GLOMERULAR EPITHELIAL-CELL COMPLEMENT RECEPTORS

Complement receptor type 1 (CR1) has previously been isolated from cul tured rat glomerular epithelial cells (GEC) by C3b affinity chromatogr aphy. In addition, the presence of Crry in GEC and in rat glomeruli ha s been demonstrated. Crry appears to be the rodent analogue of human d ecay accelerating factor, which was previously described in human GEC and in human glomeruli. In this study, the molecular biology of these rat complement receptors is examined. A specific cDNA probe for rat CR 1 was generated by reverse transcription of GEC mRNA, followed by poly merase chain reaction (PCR). The oligonucleotide primers were chosen f rom conserved regions spanning 271 bases in human and mouse CR1. A 271 -base-pair PCR product was generated from rat GEC cDNA, the nucleotide sequence of which was 70.1% and 77.2% identical to those of the respe ctive mouse and human sequences. This PCR product, designated rCR1-p, was then used to probe for CR1 mRNA. By northern blot analysis, rCR1-p hybridized to 4.5-kilobase (kb) mRNA from both cultured GEC and rat g lomeruli and also weakly hybridized to 4.5-kb CR1 mRNA from mouse sple en. In additional northern blots, a nucleotide probe for mouse Crry hy bridized to mRNA of 2.1 to 2.4 kb from rat GEC, slightly larger than t he 1.9- to 2.1-kb mouse Crry mRNA. Therefore, mRNA for CR1 and Crry ar e present in cultured rat GEC and in rat glomeruli in vivo. To further investigate the composition of rot CR1 mRNA, northern hybridizations were performed with nucleotide probes for mouse and human CR1. Althoug h the nucleotide probe for human CR1 hybridized to rat CR1 mRNA, the p robe for mouse CR1 did not. Taken together, the available data indicat e that rat CR1 has greater homology to human CR1 then to mouse CR1.