In previous studies, it has been shown that FA formation, cytoskeleton contractility, and adult stem cell differentiation. The PDMS micropost array is also ideal for studies of involvement of cytoskeleton contractility in mechanoresponsive cellular behaviors, as the PDMS microposts can serve simultaneously as force sensors to map live-cell subcellular distributions of traction forces. In this study, we proposed to apply the PDMS micropost array to study the mechanosensitivity of hESCs and how matrix mechanics could regulate pluripotency of hESCs. DNA double-strand breaks generated by ionizing radiation represent an extremely cytolethal form of DNA damage and thus pose a GSK2118436 serious threat to the preservation of genetic and epigenetic information. Cells have evolved complex DNA damage response mechanisms to ensure genomic integrity that use signaling networks to sense DSBs, arrest the cell cycle, activate DNA repair processes, and, finally, restore the original chromatin structure. Non-homologous end joining is the predominant DSB repair pathway in higher eukaryotes and operates throughout the cell cycle without the need for template DNA. NHEJ, which essentially mediates direct ligation of broken DNA ends with minimal DNA end processing, is often mutagenic because deletions and insertions can occur at sites of repair. Central to the NHEJ process is the primary recognition of DSBs by the Ku70-Ku80 heterodimer, which creates a preformed ring that sterically encircles free DNA ends without establishing sequence-specific contacts. DNA-bound Ku directs the recruitment of the catalytic subunit of the DNA-dependent protein kinase via a small helical domain at the C terminus of Ku80, resulting in the assembly of the holoenzyme DNA-PK and activation of its kinase activity. This DNA-PK complex keeps broken DNA ends in close proximity and proper alignment, providing a recruitment platform for subsequent repair factors. Signaling and repair of DNA breaks occur in the context of highly structured chromatin. The fundamental DNA packaging unit of chromatin is the nucleosome, composed of 147 bp of DNA wrapped around a histone octamer. Individual nucleosomes are joined by linker histones such as H1 and further compacted into higher-order chromatin structures by non-histone components, such as heterochromatin protein 1. Chromatin compaction acts as a physical barrier to DNA-templated processes such as transcription, and the genome is partitioned into active and inactive domains based on local chromatin fiber density. Emerging evidence suggests that the ability of repair factors to detect DNA lesions and be retained efficiently at breaks is determined by histone modifications around the DSBs and involves chromatin-remodeling events. The most prominent DNA damage induced histone modification is the phosphorylation of the C-terminal tail of H2AX. Phosphorylated H2AX seems to function as a platform to attract and retain repair proteins, such as MDC1 and 53BP1.