Time zero determination for FEL pump-probe studies based on ultrafast melting of bismuth

A common challenge for pump-probe studies of structural dynamics at X-ray free-electron lasers (XFELs) is the determination of time zero (T₀)-the time an optical pulse (e.g., an optical laser) arrives coincidently with the probe pulse (e.g., a XFEL pulse) at the sample position. In some cases, T₀ might be extracted from the structural dynamics of the sample's observed response itself, but generally, an independent robust method is required or would be superior to the inferred determination of T₀. In this paper, we present how the structural dynamics in ultrafast melting of bismuth can be exploited for a quickly performed, reliable and accurate determination of T₀ with a precision below 20 fs and an overall experimental accuracy of 50 fs to 150 fs (estimated). Our approach is potentially useful and applicable for fixed-target XFEL experiments, such as serial femtosecond crystallography, utilizing an optical pump pulse in the ultraviolet to near infrared spectral range and a pixelated 2D photon detector for recording crystallographic diffraction patterns in transmission geometry. In comparison to many other suitable approaches, our method is fairly independent of the pumping wavelength (UV-IR) as well as of the X-ray energy and offers a favorable signal contrast. The technique is exploitable not only for the determination of temporal characteristics of the experiment at the interaction point but also for investigating important conditions affecting experimental control such as spatial overlap and beam spot sizes.

High expression of ABCG2 induced by EZH2 disruption has pivotal roles in MDS pathogenesis

Both proto-oncogenic and tumor-suppressive functions have been reported for enhancer of zeste homolog 2 (EZH2). To investigate the effects of its inactivation, a mutant EZH2 lacking its catalytic domain was prepared (EZH2-dSET). In a mouse bone marrow transplant model, EZH2-dSET expression in bone marrow cells induced a myelodysplastic syndrome (MDS)-like disease in transplanted mice. Analysis of these mice identified Abcg2 as a direct target of EZH2. Intriguingly, Abcg2 expression alone induced the same disease in the transplanted mice, where stemness genes were enriched. Interestingly, ABCG2 expression is specifically high in MDS patients. The present results indicate that ABCG2 de-repression induced by EZH2 mutations have crucial roles in MDS pathogenesis.