Characterization of post‐translational modifications on lysine 9 of histone H3 variants in mouse testis using matrix‐assisted laser desorption/ionization in‐source decay

RATIONALE Post-translational modifications (PTMs) of histones result in changes to transcriptional activities and chromatin remodeling. Lysine 9 of histone H3 (H3K9) is subject to PTMs, such as methylation and acetylation, which influence histone activity during spermatogenesis. Characterization strategies for studying PTMs on H3K9 have been developed to provide epigenetic and proteomic information. Proteomic analysis has been used to limited success to study PTMs on H3K9; however, a comprehensive analytical approach is required to elucidate global patterns of PTMs of H3 variants during spermatogenesis. METHODS Intact H3 variants in mouse testis were separated by high-performance liquid chromatography on a reversed-phase column with an ion-pairing reagent. Modifications to H3K9 were identified via top-down analysis using matrix-assisted laser desorption/ionization-in source decay (MALDI-ISD). RESULTS Mono-, di-, and tri-methylations were identified at H3K9 in mouse testis and epididymis. These modifications were also observed in testis-specific histone H3 (H3t). Specifically, tri-methylation was more abundant on H3tK9 than on K9 of other H3 variants. CONCLUSIONS We introduce a method for rapid, simple, and comprehensive characterization of PTMs on the N-termini of H3 variants using MALDI-ISD. This approach provides novel and useful information, including K9 modifications on H3t, which would benefit epigenetic and proteomic research.