Porcine Fas-ligand gene: genomic sequence analysis and comparison with human gene.

Thymic Fas-ligand (FasL) cDNA and hepatic FasL genomic sequences were obtained from a 2-month-old LW pig. From these nucleotide sequences, amino acid sequence was deduced and compared with FasL sequences obtained from various animals. This comparison reveals that porcine FasL is closer to that of human, macaca and cat, and differs more from mouse and rat. The extracelluar domains of porcine and human FasL proteins appear to be functionally compatible. The complete genomic DNA sequence of porcine FasL was also compared with its human counterpart. Exons showed 80-89% nucleotide homology between pig and human, while introns showed 64-69% nucleotide homology. Sequence comparison by Harr plot analysis revealed many stretches within introns having identical sequences, suggesting that the sites may have unidentified common functions. One potential extra exon between exons 2 and 3 was located within porcine intron 2. This potential exon has no counterpart in human FasL intron 2. Whether or not this extra exon can be expressed and could cause additional immunological responses remains to be investigated. For future xenotransplantation, it is important to compare porcine and human genomic sequences, and to investigate their system compatibilities.