Fig. 1

Isoform identification and titin alternative splicing events in human skeletal muscle. a The previously reported classes of isoforms differ from each other by the inclusion/exclusion of exons 48 (included only in Novex3 isoform) and 49 (included in all the other isoforms except the long skeletal muscle N2A-isoform). Our data suggests that N2A isoform is 20 times more expressed than Novex3. All the other isoforms have a very low expression. b We identified a low number of reads connecting exon 11 to its flanking exons. On the contrary, a high number of reads connect exon 10 to exon 12 and 13, thereby skipping exon 11. In line with the RNA-Seq results, a standard RT-PCR (forward primer on exon 9 and reverse primer on exon 13, red arrows) and agarose gel electrophoresis show a very low abundance of the transcript including exon 11. M1 = 100 bp ladder. c Several RT-PCRs and agarose gel electrophoresis show a variable expression of metatranscript-only exons, confirming the RNA-Seq results. In particular, no expression of exons 163 and 165 is detected; on the contrary, all the other RT-PCRs result in a detectable band corresponding to the expected size. M1 = 100 bp ladder; M2 = 1 kb ladder; d = PCR from a control DNA; c = RT-PCR from a control cDNA (obtained by a retrotranscription of RNA extracted from gracilis muscle). d Titin repeated region is composed of nine exons/blocks (here represented by different colors and named B1-B9) repeated three times. Within the repeated region, linear expression of consecutive exons has been detected. Moreover, a number of alternative splicing events has been identified. e We detected alternative splicing acceptors or donors leading to subtle changes in the produced protein. The splice-site strength for canonical splice sites (5′ss and 3′ss) as well as for alternative sites (alt 5′ss, alt 3′ss) has been calculated by Human Splice Finder (HSF)