Plectin transcript diversity: identification and tissue distribution of variants with distinct first coding exons and rodless isoforms.

Plectin is a widely expressed protein that is very large in size and that has all the attributes of a multifunctional crosslinking and organizing element of the cytoskeleton. It displays a multidomain structure, versatile binding activities, and subcellular localizations that enable it to strengthen cells against mechanical stress forces. Moreover, hereditary gene defects in plectin cause epidermolysis bullosa simplex (EBS)-MD, a severe skin blistering disease with muscular dystrophy. Here we report the analysis of the exonintron organization of the rat plectin gene and the identification of several different isoforms on the transcriptional level. We show that of 35 coding exons identified, 4 serve as alternative first exons splicing into the same successive exon 2, which is the first of 7 exons encoding a highly conserved actin-binding domain. RNase protection mapping of transcripts containing 3 of the identified 4 alternate first exons revealed their coexpression in rat glioma C6 cells and in a series of different rat tissues that we examined. Significant variations in expression levels of first exons indicated the possibility of tissue-specific promoter usage. In addition, plectin splice variants lacking exon 31 (> 3 kb), which encodes the entire rod domain of the molecule, were identified in a variety of rat tissues. This study provides first insights into a complex plectin gene regulatory machinery with similarities to that of dystrophin.