Dissecting the cellular response to DNA damage using an innovative “laser-scissors” system

Proper DNA damage repair is essential for maintaining genomic integrity and stability of all living organisms. In instances of improper or inefficient repair by the cell, DNA double-strand breaks (DSBs), the most lethal form of DNA damage, can cause mutations and truncations of genetic material, and lead to human diseases such as cancer and premature aging. A great deal of research effort has been focused on the mechanism of DSB repair, using a variety of techniques to induce DSBs in cells. Examples of these techniques include gamma radiation and radiomimetic drugs. While effective in creating DSBs, these conventional techniques lack the precision and control necessary for investigating finer details of DSB repair processes. A newly developed “laser-scissors” technology overcomes drawbacks of traditional DNA damaging methods by inducing clustered DSBs in specific locations in cells in a user-defined manner. With advanced microscopic techniques, including live cell imaging, this laser method can visualize the DNA damage response in individual cells with high sensitivity and precision. During my undergraduate research in Dr. Zhongsheng You’s laboratory in the Department of Cell Biology and Physiology at Washington University, I used a customized “laser-scissors” system to study the human DNA damage response. Under the supervision of Dr. You, I investigated the recruitment of the DNA repair protein 53BP1 (p53 binding protein 1) to DSBs. Using laser irradiation and imaging tools, we demonstrated that 53BP1 damage recruitment requires the function of the MMSET protein, which modifies the histone protein H4 in the chromatin region flanking the DSB ends, creating binding sites for 53BP1. The role of MMSET in DNA repair may provide an underlying mechanism for the function of MMSET in the formation of multiple myelomas. Thus, the “laser-scissors” system has lead to important insights into DSB repair and its relation to cancer