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. 2023 Dec 12;12(24):2819. doi: 10.3390/cells12242819

Figure 3.

Figure 3

Cassette exon: aging-regulated alternative splicing of SIRT1 and ING1 genes. (a) The human SIRT1 genomic organization and its aging-related splicing isoforms. SIRT1-v1 isoform includes nine exons and no cassette exons (aqua coloured boxes). SIRT1-v2 includes eight exons, and the first exon was named Exon-1′ (E1′). SIRT1-v3 isoform includes seven exons with the Exon-4′ (E4′) in-between exon 4 and 5. (b) The human IGF1 genomic organization (IGF1) and its aging-related splicing isoforms (Ea, Eb, and Ec/MGF). The IGF1-Ea isoform shows skipping of the whole exon 5. The IGF1-Eb isoform shown includes the whole exon 5. The Ec/MGF isoform contains the N-terminal part of exon 5 (consisting of 49 nucleotides, shown as a gray box) and exon 6. Exon 5 inclusion causes the occurrence of an altered C-terminal amino acid sequence as a result of a shift in the reading frame. Yellow box: constitutive exon; solid line: intron; dotted lines: alternative splicing patterns; upwards red arrow: upregulated expression; downwards blue arrow: downregulated expression.