Quantification of gammaH2AX foci in response to ionising radiation

Mah, Li-Jeen, Vasireddy, Raja S., Tang, Michelle M., Georgiadis, George T., El-Osta, Assam, & Karagiannis, Tom C. (2010) Quantification of gammaH2AX foci in response to ionising radiation. Journal of Visualized Experiments, 38, e1957-1.

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DNA double-strand breaks (DSBs), which are induced by either endogenous metabolic processes or by exogenous sources, are one of the most critical DNA lesions with respect to survival and preservation of genomic integrity. An early response to the induction of DSBs is phosphorylation of the H2A histone variant, H2AX, at the serine-139 residue, in the highly conserved C-terminal SQEY motif, forming gammaH2AX(1). Following induction of DSBs, H2AX is rapidly phosphorylated by the phosphatidyl-inosito 3-kinase (PIKK) family of proteins, ataxia telangiectasia mutated (ATM), DNA-protein kinase catalytic subunit and ATM and RAD3-related (ATR)(2). Typically, only a few base-pairs (bp) are implicated in a DSB, however, there is significant signal amplification, given the importance of chromatin modifications in DNA damage signalling and repair. Phosphorylation of H2AX mediated predominantly by ATM spreads to adjacent areas of chromatin, affecting approximately 0.03% of total cellular H2AX per DSB(2,3). This corresponds to phosphorylation of approximately 2000 H2AX molecules spanning approximately 2 Mbp regions of chromatin surrounding the site of the DSB and results in the formation of discrete gammaH2AX foci which can be easily visualized and quantitated by immunofluorescence microscopy(2). The loss of gammaH2AX at DSB reflects repair, however, there is some controversy as to what defines complete repair of DSBs; it has been proposed that rejoining of both strands of DNA is adequate however, it has also been suggested that re-instatement of the original chromatin state of compaction is necessary(4-8). The disappearence of gammaH2AX involves at least in part, dephosphorylation by phosphatases, phosphatase 2A and phosphatase 4C(5,6). Further, removal of gammaH2AX by redistribution involving histone exchange with H2A.Z has been implicated(7,8). Importantly, the quantitative analysis of gammaH2AX foci has led to a wide range of applications in medical and nuclear research. Here, we demonstrate the most commonly used immunofluorescence method for evaluation of initial DNA damage by detection and quantitation of gammaH2AX foci in gamma-irradiated adherent human keratinocytes(9)

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ID Code: 78905
Item Type: Journal Article
Refereed: Yes
Keywords: DNA, H2AFX protein, human, histone, confocal microscopy
DOI: 10.3791/1957
ISSN: 1940-087X
Subjects: Australian and New Zealand Standard Research Classification > MEDICAL AND HEALTH SCIENCES (110000) > ONCOLOGY AND CARCINOGENESIS (111200)
Divisions: Current > QUT Faculties and Divisions > Faculty of Health
Copyright Owner: Copyright 2010 Journal of Visualized Experiments
Deposited On: 25 Nov 2014 00:51
Last Modified: 26 Nov 2014 03:47

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