Keratins are a family of intermediate filament-forming proteins highly specific to epithelial cells. A combination of expressed keratin genes is a defining property of the epithelium belonging to a certain type, organ/tissue, cell differentiation potential, and at normal or pathological conditions. In a variety of processes such as differentiation and maturation, as well as during acute or chronic injury and malignant transformation, keratin expression undergoes switching: an initial keratin profile changes accordingly to changed cell functions and location within a tissue as well as other parameters of cellular phenotype and physiology. Tight control of keratin expression implies the presence of complex regulatory landscapes within the keratin gene loci. Here, we highlight patterns of keratin expression in different biological conditions and summarize disparate data on mechanisms controlling keratin expression at the level of genomic regulatory elements, transcription factors (TFs), and chromatin spatial structure.

Trisomy is the presence of one extra copy of an entire chromosome or its part in a cell nucleus. In humans, autosomal trisomies are associated with severe developmental abnormalities leading to embryonic lethality, miscarriage or pronounced deviations of various organs and systems at birth. Trisomies are characterized by alterations in gene expression level, not exclusively on the trisomic chromosome, but throughout the genome. Here, we applied the high-throughput chromosome conformation capture technique (Hi-C) to study chromatin 3D structure in human chorion cells carrying either additional chromosome 13 (Patau syndrome) or chromosome 16 and in cultured fibroblasts with extra chromosome 18 (Edwards syndrome). The presence of extra chromosomes results in systematic changes of contact frequencies between small and large chromosomes. Analyzing the behavior of individual chromosomes, we found that a limited number of chromosomes change their contact patterns stochastically in trisomic cells and that it could be associated with lamina-associated domains (LAD) and gene content. For trisomy 13 and 18, but not for trisomy 16, the proportion of compacted loci on a chromosome is correlated with LAD content. We also found that regions of the genome that become more compact in trisomic cells are enriched in housekeeping genes, indicating a possible decrease in chromatin accessibility and transcription level of these genes. These results provide a framework for understanding the mechanisms of pan-genome transcription dysregulation in trisomies in the context of chromatin spatial organization.

Cohesin organizes the genome into spatially segregated loops and topologically associated domains by loop extrusion. In addition, it ensures cohesion of sister chromatids after replication. Thus, cohesin is expected to limit chromatin dynamics by ensuring cohesion and compacting chromatin in the interphase. Nonetheless, loop extrusion is an example of chromatin dynamics; thus, cohesin could promote the dynamics of genomic loci at the scale of individual loops and contact domains. Moreover, given that the extruding activity of cohesin after replication is supplemented by its cohesive activity, the impact of cohesin on chromatin dynamics in different phases of the cell cycle may vary. Of particular interest is the cohesin’s role in the regulation of the dynamics of damaged chromatin, which remains insufficiently studied. Here, we visualized a genomic locus using the CRISPR-Sirius system in human cells with auxin-induced depletion of the cohesin subunit RAD21. Cohesin depletion increased the local spatial dynamics of the visualized locus on a time scale of fractions of a second to one minute. This effect was observed in both replicated and unreplicated chromatin. However, the increase in the mobility of the visualized locus upon cohesin depletion was more pronounced in the former. In addition, we showed that cohesin depletion did not affect the local mobility of double-strand break repair foci visualized using a fluorescent fragment of the repair factor 53BP1. Cohesin depletion did not affect the local mobility of repair foci in either replicated or unreplicated chromatin. The results indicate that cohesin constrains local spatial dynamics of genomic loci. At the same time, cohesive activity of cohesin is not indispensable for restricting chromatin dynamics, although it enhances the confinement effect. On the other hand, repair foci are less mobile structures than point chromatin loci, and cohesin does not affect their dynamics on the studied time scales.

Enhancer-promoter interactions occur in the chromatin loci delineated by the CCCTC-binding zinc-finger protein CTCF. CTCF binding is frequently perturbed in genetic disorders and cancer, allowing for misregulation of genes. Here, we developed a panel of chimeric proteins consisting of either full-length or truncated CTCF fused with programmable DNA-binding module dCas9 and fluorescent tracker EGFP. We found that the recruitment of a chimeric protein based on the CTCF N-terminal domain and two zinc-finger domains to the human HOXD locus leads to the de novo formation of a spatial contact with a nearby cohesin/CTCF-bound region, anchoring several chromatin loops. This chimeric protein did not show binding to CTCF motifs and did not affect the epigenetic and transcription profile of the locus. Recruitment of this chimeric protein is also able to restore chromatin loops, lost after deletion of an endogenous CTCF-binding site. Together, our data indicate that the ectopic recruitment of the CTCF N-terminal part could be an appropriate tool for 3D genome engineering.