Alternative exon usage in the 3' region of a single gene generates glycosylphosphatidylinositol-anchored and transmembrane forms of rat decay-accelerating factor.

Abstract

Several cDNA clones encoding genetic homologues of human decay-accelerating factor (DAF) were isolated from rat testis cDNA libraries and reverse transcription-polymerase chain reaction products. Sequence analysis revealed that rat DAF exists as two membrane forms, a glycosylphosphatidylinositol (GPI)-anchored and a transmembrane (TM) form. Southern blotting analysis showed that GPI- and TM-form mRNAs of rat DAF are derived from a single gene, as is the case for guinea pig, though both forms of mouse DAF mRNA are derived from two genes. Gene analysis of the C-terminal region of rat DAF indicated that both forms of mRNA are presumably generated by alternative splicing of exons which encode a GPI/3'-untranslated (3'UT) region and a TM/3'UT region in the 3' end of the Ser/Thr-rich region. Northern blot analysis indicated that rat GPI-DAF mRNA was present in all tissues examined except for liver, while rat TM-DAF mRNA was preferentially expressed in testis. Infant rat testis barely expressed TM-DAF and membrane cofactor protein (MCP) but highly expressed 5I2 antigen (5I2Ag, rat Crry). However, adult rat testis showed increased expression of the 1.6-kb transcript of rat GPI-DAF, TM-DAF, MCP, and the 0.7-kb transcript of CD59, with a decreased level of 5I2Ag expression. These results suggest that rat 5I2Ag/Crry may play an important role in regulating complement activation during the early stages of testis development, and that DAF, MCP, and CD59 expressed in testis may enable sperm to survive complement attack in the mucus of the female genital organ, and/or to interact with an ovum.