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CTCF establishes discrete functional chromatin domains at the Hox clusters during differentiation

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Science  27 Feb 2015:
Vol. 347, Issue 6225, pp. 1017-1021
DOI: 10.1126/science.1262088

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Keeping repressed genes repressed

Hox genes confer positional identity to cells and tissues. Maintaining precise spatial patterns of Hox gene expression is vital during metazoan development. The transcriptional repressor CTCF is involved in the regulation of chromatin architecture. Narendra et al. show that a CTCF protein binding site insulates regions of active and repressed Hox gene expression from each other. This protects heterochromatin containing repressed Hox genes from the encroaching spread of active chromatin. The CTCF protein appears to organize the active and repressed chromatin regions into distinct architectural domains.

Science, this issue p. 1017

Abstract

Polycomb and Trithorax group proteins encode the epigenetic memory of cellular positional identity by establishing inheritable domains of repressive and active chromatin within the Hox clusters. Here we demonstrate that the CCCTC-binding factor (CTCF) functions to insulate these adjacent yet antagonistic chromatin domains during embryonic stem cell differentiation into cervical motor neurons. Deletion of CTCF binding sites within the Hox clusters results in the expansion of active chromatin into the repressive domain. CTCF functions as an insulator by organizing Hox clusters into spatially disjoint domains. Ablation of CTCF binding disrupts topological boundaries such that caudal Hox genes leave the repressed domain and become subject to transcriptional activation. Hence, CTCF is required to insulate facultative heterochromatin from impinging euchromatin to produce discrete positional identities.

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