Alternative splicing creates sex-specific transcripts and truncated forms of the furin protease in the parasite Dirofilaria immitis

Many extracellular proteins are activated by specific cleavage with an endo protease. In nematodes, several proteins are cleaved after RX(K/R)R, the re cognition site for the subtilisin-like proprotein convertases, furin and bl isterase. To characterize furin in the parasitic nematode Dirofilaria immit is, we determined the sequence of the difur gene and its multiple transcrip ts. The gene spans 11 kb; encodes 16 exons and has a complex pattern of alt ernative splicing which generates at least 16 distinct mRNAs. The major tra nscript is a 4.4 kb mRNA which codes for a protein of 834 aa with an unusua lly long prodomain of 254 aa. Sex-specific splice variants of difur were ob served by RT-PCR. The three female-specific and five male-specific transcri pts are the first reported examples of sex-specific splicing in parasitic n ematodes. This suggests that nematodes have sex-specific factors which regu late RNA splicing. Other splice variants are predicted to alter the phospho rylation and localization of the protease. Alternative splicing after the p rodomain encodes a truncated protein that may be an inhibitor and/or substr ate of Difurin. (C) 1999 Elsevier Science B.V. All rights reserved.