ABSTRACT
The spatial arrangement of chromatin is linked to the regulation of nuclear processes. One striking aspect of nuclear organization is the spatial segregation of heterochromatic and euchromatic domains. The mechanisms of this chromatin segregation are still poorly understood. In this work, we investigated the link between the primary genomic sequence and chromatin domains. We analyzed the spatial intranuclear arrangement of a human artificial chromosome (HAC) in a xenospecific mouse background in comparison to an orthologous region of native mouse chromosome. The two orthologous regions include segments that can be assigned to three major chromatin classes according to their gene abundance and repeat repertoire: (1) gene-rich and SINE-rich euchromatin; (2) gene-poor and LINE/LTR-rich heterochromatin; and (3) gene-depleted and satellite DNA-containing constitutive heterochromatin. We show, using fluorescence in situ hybridization (FISH) and 4C-seq technologies, that chromatin segments ranging from 0.6 to 3 Mb cluster with segments of the same chromatin class. As a consequence, the chromatin segments acquire corresponding positions in the nucleus irrespective of their chromosomal context, thereby strongly suggesting that this is their autonomous property. Interactions with the nuclear lamina, although largely retained in the HAC, reveal less autonomy. Taken together, our results suggest that building of a functional nucleus is largely a self-organizing process based on mutual recognition of chromosome segments belonging to the major chromatin classes.
Subject(s)
Cell Nucleus/genetics , Chromosomes, Artificial, Human/metabolism , Euchromatin/metabolism , Fibroblasts/metabolism , Heterochromatin/metabolism , Retina/metabolism , Animals , Cell Line, Transformed , Cell Nucleus/metabolism , Cell Nucleus/ultrastructure , Chromosomes, Artificial, Human/ultrastructure , Euchromatin/classification , Euchromatin/ultrastructure , Fibroblasts/ultrastructure , Gene Expression Profiling , Gene Expression Regulation , Heterochromatin/classification , Heterochromatin/ultrastructure , Humans , In Situ Hybridization, Fluorescence , Mice , Primary Cell Culture , Retina/ultrastructureABSTRACT
One of the biggest obstacles to gene therapy is the delivery of the therapeutic gene to the target tissue so that it is appropriately expressed. In his Perspective, Willard looks at the potential advantages of using a human artificial chromosome to maintain expression of a therapeutic gene and discusses some of the hurdles yet to be overcome before this gene delivery system can be tried out in the clinic.
