HIGHER PROPORTION OF INTACT EXON-9 CFTR MESSENGER-RNA IN NASAL EPITHELIUM COMPARED WITH VAS-DEFERENS

The 5-thymidine (5T) variant of the cystic fibrosis transmembrane cond uctance regulator (CFTR) intron 8 polypyrimidine tract (IVS8-T tract) is the most frequent CFTR gene alteration identified in men with conge nital bilateral absence of vas deferens (CBAVD), This alternative spli cing Variant gives rise to two transcripts, one normal with exon 9 int act and the other with in-frame deletion of exon 9, That CBAVD men usu ally have none of the other clinical signs of classical cystic fibrosi s (CF) suggests less functional CFTR is produced in the reproductive t ract than in other CF-associated organs, Nasal epithelia and segments of vas deferens were obtained from healthy, previously vasectomized me n who presented for vasectomy reversal. Quantitative RT-PCR was perfor med on these specimens, with the region of CFTR cDNA spanning exon 9 a mplified, For both nasal and vasal tissues, a strong positive correlat ion was found between the length of the IVS8-T tract and the proportio n of mRNA with exon 9 intact, In addition, within the same subject, a significantly higher level of transcripts lacking exon 9 was found in vas deferens than nasal epithelia, regardless of the IVS8-T genotype, These findings suggest that the splicing of CFTR precursor mRNA is les s efficient in vasal epithelia compared with respiratory epithelia, Th us, differential splicing efficiency between the various tissues which express CFTR provides one possible explanation for the reproductive t ract abnormalities observed in infertile men with CFTR gene alteration s but without other clinical manifestations of CF.