ABSTRACT
The eukaryotic genome is folded into higher-order conformation accompanied with constrained dynamics for coordinated genome functions. However, the molecular machinery underlying these hierarchically organized three-dimensional (3D) chromatin architecture and dynamics remains poorly understood. Here by combining imaging and sequencing, we studied the role of lamin B1 in chromatin architecture and dynamics. We found that lamin B1 depletion leads to detachment of lamina-associated domains (LADs) from the nuclear periphery accompanied with global chromatin redistribution and decompaction. Consequently, the inter-chromosomal as well as inter-compartment interactions are increased, but the structure of topologically associating domains (TADs) is not affected. Using live-cell genomic loci tracking, we further proved that depletion of lamin B1 leads to increased chromatin dynamics, owing to chromatin decompaction and redistribution toward nucleoplasm. Taken together, our data suggest that lamin B1 and chromatin interactions at the nuclear periphery promote LAD maintenance, chromatin compaction, genomic compartmentalization into chromosome territories and A/B compartments and confine chromatin dynamics, supporting their crucial roles in chromatin higher-order structure and chromatin dynamics.
Subject(s)
Humans , Chromatin , Chromosomes , Genome , Lamin Type B/geneticsABSTRACT
The role of recurrent chromosomal translocations in pathogenesis is well characterized in many leukemia subtypes; however, the factors leading to such preferential gene fusions are yet to be understood. The proximity of the genetic regions is considered important for genetic exchange, and interphase molecular cytogenetic methods can be employed to measure the same. The interphase genomic location of gene pairs taking part in translocations which are non-randomly associated with leukemia subtypes was studied for the extent of proximity by measuring relative distance and radial location. The FISH (Fluorescence In Situ Hybridization) signals corresponding to gene pairs were scored for relative distance and percentage of possible translocation pairs showing proximity which was found higher for BCR-ABL, PML-RARA and AML-ETO. The radial position of the gene pairs was also recorded to see if there is any preferred location in terms of nuclear centre or periphery for translocation partners. The results suggested no preferential location of any of the gene pairs in periphery or centre of the interphase nucleus, rather random distribution was observed for all the three cases. We report here the use of simple interphase FISH method to assess the interphase proximity of gene fusion pairs which can be further employed for other translocations.
ABSTRACT
Interphase chromosomes have been shown to occupy discrete regions of the nucleus denominated chromosome territories (CTs), their active genes being preferentially positioned on the surfaces of these CTs, where they are accessible to transcriptional machinery. By means of FISH (Fluorescence in situ Hybridization), we analyzed the CCND1 and HER-2/neu gene positions within the CTs and their relationship with gene amplification and protein over-expression in esophageal and gastric cancers. The CCND1 and HER-2/Neu genes were more often positioned at the periphery (mean frequency of 60 percent-83 percent) of the CTs in tumor tissues of the esophagus and stomach. Moreover, this positioning revealed no association with either gene amplification or the protein over-expression status of these genes, although, in esophageal carcinoma, Kappa statistics showed a moderate agreement between amplification of the CCND1 gene (Kappa = 0.400) and its location within the CT, as well as with over-expression of the corresponding protein (Kappa = 0.444). Thus, our results suggest that gene positioning in interphase chromosomes does not follow a definitive pattern neither does it depend only on gene transcriptional activity. Apparently, this positioning could be both gene- and tissue-specific, and depends on other factors acting together, such as dense-gene, chromosome size, chromatin structure, and the level and stability of its expression.