Single genomic loci in human chromosomes are often related to specific cellular functions, human genetic diseases and pathogen infections. Live visualization of single genomic loci would help to elucidate the spatiotemporal positions, dynamics and function of different loci and offer understanding of genome architecture and regulation. However, imaging of single genomic loci in live cells is currently challenging.

In a joint study with Prof. ZHANG Xian'en from Institute of Biophysics of the Chinese Academy of Sciences, Prof. CUI Zongqiang from Wuhan Institute of Virology of the Chinese Academy of Sciences has reported a novel approach to allow the visualization of single genomic loci in live cells. This approach combines the sequence-specific recognition of transcription activator-like effectors (TALEs) with the single-particle sensitivity of quantum dots (QDs). Compared with zinc-finger proteins or engineered meganucleases, TALEs are easier to design and optimize for the purpose of sequence-specific binding and labelling.

In this work, they designed and selected a pair of TALEs for targeting adjacent sequences of the HIV-1 proviral DNA integrated within the chromosomes of human U1 cells, and use bioorthogonal ligation reactions to label them with different QDs. These QD-labelled TALEs are able to enter the cell nucleus to provide fluorescent signals to identify single gene loci. The study shows for the first time that the Diels–Alder cycloaddition can be used for labelling TALEs with QDs in live cells.

Using their live cell genomic labelling technique they were able to map the HIV-1 provirus loci in live U1 cells. Two HIV-1 provirus loci were imaged and determined within one U1 cell. The scientists have developed a method for the live cell imaging of single genomic loci by combining TALE technology with QD labelling techniques, and believe that this novel method for examining genomic loci provides a tool for elucidating the dynamics and mechanisms of single genomic loci.

The results have been published in Nature Communications entitled "Live cell imaging of single genomic loci with quantum dot-labeled TALEs".

This work was supported by National Natural Science Foundation of China, Youth Innovation Promotion Association of the Chinese Academy of Sciences and the Key Program of the Chinese Academy of Sciences. Researchers from Beijing University of Chemical Technology also participated in this study.

Schematic of imaging genomic loci with quantum dot-labelled TALEs.  Image by CUI Zongqiang

Contact
CUI Zongqiang
E-mail: czq@wh.iov.cn
Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan 430071, China. （http://english.whiov.cas.cn/）