Schematic representation of the intron/exon structure organization of cow CSN1S1 and mouse Csn1s1 genes (panel A) and of the corresponding matured transcripts (panel B) found in the mammary tissue of C57BL/6J and SEG/Pas mouse strains. Open bars represent introns; exons are depicted by large black (3'and 5'untranslated regions) or grey (exons encoding preproteins) boxes, hatched blocks indicate potentially skipped sequence, pink and yellow blocks refer to repeats of exon 16 and no-fill blocks represent exons that are constitutively absent from mRNA according to [29, 37]. Numbers above blocks indicate exon number; numbers below (italics) indicate exon size (in bp). Vertical green arrows indicate exons (or sequences) skipped (or included) during the course of the splicing process. C57BL/6J: a, deletion of the first codon of exon 8 and of the first 57 nucleotides of exon 21, b: exon-skipping of exon 9 and 10, c: exon-skipping of exon 16.3. SEG/Pas: a', deletion of the first 57 nucleotides of exon 21; b', deletion of the first codon of exon 8 and exon-skipping of exons 9, 16.14 and 17; c', insertion of the last 33 nucleotides of intron 10.