SUMMARY Histone modifications influence higher-order chromatin structures at individual epigenomic states and chromatin environments to regulate gene expression. However, genome-wide higher-order chromatin structures shaped by different histone modifications remain poorly characterized. With stochastic optical reconstruction microscopy (STORM), we characterized the higher-order chromatin structures at their epigenomic states, categorized into three major types in interphase: histone acetylation marks form spatially segregated nanoclusters, active histone methylation marks form spatially dispersed larger nanodomains, and repressive histone methylation marks form condensed large aggregates. These distinct structural characteristics are also observed in mitotic chromosomes. Furthermore, active histone marks coincide with less compact chromatin and exhibit a higher degree of co-localization with other active marks and RNA polymerase II (RNAP II), while repressive marks coincide with densely packed chromatin and spatially distant from repressive marks and active RNAP II. Taken together, super-resolution imaging reveals three distinct chromatin structures at various epigenomic states, which may be spatially coordinated to impact transcription.

IntroductionFabricating nanostructured surface topography represents the mainstream approach to induce osteogenesis for the next-generation bone implant. In the past, the bone implant was designed to minimize host repulsive reactions in order to acquire biocompatibility. However, increasing reports indicate that the absence of an appropriate immune response cannot acquire adequate osseointegration after implantation in vivo.Materials and methodsWe prepared different topographies on the surface of titanium (Ti) specimens by grinding, etching and anodizing, and they were marked as polished specimen (P), specimen with nanotubes (NTs) in small diameters (NT-30) and specimen with NTs in large diameters (NT-100). We evaluated the ability of different topographies of the specimen to induce osteogenic differentiation of mice bone marrow mesenchymal stem cells (BMSCs) in vitro and to induce osseointegration in vivo. Furthermore, we investigated the effect of different topographies on the polarization and secretion of macrophages, and the effect of macrophage polarization on topography-induced osteogenic differentiation of mice BMSCs. Finally, we verified the effect of macrophage polarization on topography-induced osseointegration in vivo by using Cre*RBP-Jfl/fl mice in which classically activated macrophage was restrained.ResultsThe osteogenic differentiation of mice BMSCs induced by specimen with different topographies was NT-100>NT-30>P, while the osseointegration induced by specimen with different topographies in vivo was NT-30>NT-100>P. In addition, specimen of NT-30 could induce more macrophages to M2 polarization, while specimen of P and NT-100 could induce more macrophages to M1 polarization. When co-culture mice BMSCs and macrophages on specimen with different topographies, the osteogenic differentiation of mice BMSCs was NT-30>NT-100≥P. The osseointegration induced by NT-100 in Cre*RBP-Jfl/fl mice was much better than that of wild type mice.ConclusionIt is suggested that the intrinsic immunomodulatory effects of nanomaterials are not only crucial to evaluate the in vivo biocompatibility but also required to determine the final osseointegration. To clarify the immune response and osseointegration may be beneficial for the designation and optimization of the bone implant.

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