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Hereditas(Beijing) ›› 2021, Vol. 43 ›› Issue (8): 775-791.doi: 10.16288/j.yczz.21-132

• Orginal Articles • Previous Articles     Next Articles

Serial deletions of tandem reverse CTCF sites reveal balanced HOXD regulatory landscape of enhancers

Ling Wang(), Jinhuan Li, Haiyan Huang(), Qiang Wu()   

  1. Center for Comparative Biomedicine, Key laboratory of Systems Biomedicine (Ministry of Education), Institute of Systems Biomedicine, Shanghai Jiao Tong University, Shanghai 200240, China
  • Received:2021-04-11 Revised:2021-05-12 Online:2021-08-20 Published:2021-06-30
  • Contact: Huang Haiyan,Wu Qiang E-mail:wanglingmail0613@163.com;hy_huang@sjtu.edu.cn;qwu123@gmail.com
  • Supported by:
    Supported by the National Natural Science Foundation of China Nos(31800636);Supported by the National Natural Science Foundation of China Nos(31630039);Supported by the National Natural Science Foundation of China Nos(91940303);Science and Technology Commission of Shanghai Municipality No(19JC1412500)

Abstract:

The genome architectural protein CTCF (CCCTC-binding factor) not only mediates long-distance chromatin interactions between distal enhancers and target promoters, but also functions as an important insulator-binding factor to block improper enhancer activation of non-target promoters, and is thus of great significance to transcriptional regulation of developmental genes. The Hox (Homeobox) gene family plays an important role in the development of the brain, bones, and limbs. The spatiotemporal colinear expression of the HOXD cluster along the proximal-distal axis of limbs is regulated by two clusters of enhancers known as super-enhancers located in the flanking regulatory regions. We focused on the HOXD cluster to explore the architectural role of CTCF in transcriptional regulation of developmental genes. The HOXD cluster contains 9 paralogous genes intermixed with a series of CBS (CTCF-binding site) elements. Using the CRISPR DNA-fragment editing system, we generated a series of single-cell HEK293T clones with deletion of increasing numbers of reverse CBS elements. RNA-seq experiments revealed decreased levels of HOXD gene expression. In addition, chromosome conformation capture experiments revealed increased long-distance chromatin interactions between HOXD and the upstream enhancer cluster and corresponding decreased interactions between HOXD and the downstream enhancer cluster. Thus, tandem reverse CTCF sites function as insulators to maintain HOXD regulatory balance between the upstream and downstream enhancer clusters. This study has interesting implications on the precise gene expression control of the Hox family during animal development.

Key words: HOXD gene cluster, CTCF site, balanced regulatory mechanism, enhancer, insulator