Epigenetic modifications of histones (methylation, acetylation, phosphorylation, etc.) are of great importance in determining the functional state of chromatin. Changes in epigenome underlay all basic biological processes, such as cell division, differentiation, aging, and cancerous transformation. Post-translational histone modifications are mainly studied by immunoprecipitation with high-throughput sequencing (ChIP-Seq). It enables an accurate profiling of target modifications along the genome, but suffers from the high cost of analysis and the inability to work with living cells. Fluorescence microscopy represents an attractive complementary approach to characterize epigenetics. It can be applied to both live and fixed cells, easily compatible with high-throughput screening, and provide access to rich spatial information down to the single cell level. In this review, we discuss various fluorescent probes for histone modification detection. Various types of live-cell imaging epigenetic sensors suitable for conventional as well as super-resolution fluorescence microscopy are described. We also focus on problems and future perspectives in the development of fluorescent probes for epigenetics.

Telomerase RNA has long been considered to be a noncoding component of telomerase. However, the expression of the telomerase RNA gene is not always associated with telomerase activity. The existence of distinct TERC gene expression products possessing different functions were demonstrated recently. During biogenesis, hTR is processed by distinct pathways and localized in different cell compartments, depending on whether it functions as a telomerase complex component or facilitates antistress activities as a noncoding RNA, in which case it is either processed in the mitochondria or translated. In order to identify the factors responsible for the appearance and localization of the exact isoform of hTR, we investigated the roles of the factors regulating transcription DSIF (Spt5) and NELF-E; exosome-attracting factors ZCCHC7, ZCCHC8, and ZFC3H1; ARS2, which attracts processing and transport factors; and transport factor PHAX during the biogenesis of hTR. The data obtained revealed that ZFC3H1 participates in hTR biogenesis via pathways related to the polyadenylated RNA degradation mechanism. The data revealed essential differences that are important for understanding hTR biogenesis and that are interesting for further investigations of new, therapeutically significant targets.

Genetically encoded photosensitizers are widely used in fundamental research and translational medicine due to their ability to generate reactive oxygen species (ROS) after photosensitizing. Previously, it was shown in mice that red dimeric fluorescent protein KillerRed is a potential photosensitizer that can be used for photodynamic therapy of cancer. In addition, it was demonstrated that HeLa cells expressing KillerRed fused to histone H2B cease proliferation upon illumination. A DNA repair protein, X-ray repair cross-complementing protein 1 (XRCC1), redistributed in the cell nuclei, indicating that the mechanism of phototoxic action of the construct involved DNA breaks generation. Here, we have constructed and tested a new genetically encoded photosensitizer molecule which introduces DNA breaks and activates the repair system in cancer-derived and embryonic cell lines more efficiently than previously described. The molecule consists of two parts: a SuperNova2 (monomeric mutant of KillerRed with enhanced phototoxicity) and methyl-CpG binding protein MECP2. The complex activates XRCC1 redistribution after illumination with lower power compared to the previously used construct. We suppose it can be explained by the tighter contact between photosensitizer and DNA. In addition, we hypothesize that the system should be error-prone for the expressed genes as it is targeted to the DNA which is silenced by methylation. Taking everything into consideration, the new genetically encoded construct has shown the improved ability to generate DNA breaks in the cancer cell lines.