Lineage potential is triggered by lineage-specific transcription factors in association with changes in the chromatin structure. Histone H3.3 variant is thought to play an important role in the regulation of lineage-specific genes. To elucidate the function of H3.3 in myogenic differentiation, we forced the expression of GFP-H3.1 to alter the balance between H3.1 and H3.3 in mouse C2C12 cells that could be differentiated into myotubes. GFP-H3.1 replaced H3.3 in the regulatory regions of skeletal muscle (SKM) genes and induced a decrease of H3K4 trimethylation (H3K4me3) and increase of H3K27 trimethylation (H3K27me3). Similar results were obtained by H3.3 knockdown. In contrast, MyoD-dependent H3.3 incorporation into SKM genes in fibroblasts induced an increase of H3K4me3 and H3K27me3. In mouse embryos, a bivalent modification of H3K4me3 and H3K27me3 was formed on H3.3-incorporated SKM genes before embryonic skeletal muscle differentiation. These results suggest that lineage potential is established through a selective incorporation of specific H3 variants that governs the balance of histone modifications.
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