DIFFERENT LA SS-B MESSENGER-RNA ISOFORMS ARE EXPRESSED IN SALIVARY-GLAND TISSUE OF PATIENTS WITH PRIMARY SJOGRENS-SYNDROME/

Recently we isolated a La/SS-B mRNA isoform from a cDNA Library made f rom peripheral blood lymphocytes of a patient with primary Sjogren's S yndrome. In the La/SS-B mRNA isoform the exon 1 was replaced. The alte rnative exon was termed exon 1'. Genomic analysis showed that the exon 1' La mRNA was the result of a promotor-switch in combination with al ternative splicing. Due to the unusual structure of the exon 1' La/SS- B mRNA, the function and the behaviour under physiological and pathoph ysiological conditions in tissue of patients with primary Sjogren's sy ndrome or Systemic Lupus Erythematosus remained obscure. Therefore ass ays were established allowing a qualitative and quantitative estimatio n of expression of the exon 1 and 1' La mRNA form, including in situ a nd dot blot hybridization as well as reversed PCR. Both mRNA forms wer e found to represent finally processed cytoplasmic mRNAs belonging to the abundant class of mRNAs. They were expressed and regulated in para llel. A ratio exon 1 to 1'between 1:1 and 5:1 was determined. Both mRN A forms were downregulated in quiescent cells and upregulated in activ ated and proliferating cells including non-keratized stratified squamo us epithelial, endothelial, salivary gland as well as infiltrating cel ls. (C) 1996 Academic Press Limited