The endothelial cells lining our cardiovascular system are constantly affected by shear stress, which can alter both the morphology and biological activity of the cells. Methods to study the basic shear stress response by creating stable flow profiles on the macro scale are well established, but they do not allow the generation of controlled high precision flow profiles. The emergence of microfluidic devices has enabled well-defined individual cellular response studies on endothelial cells in scale-relevant tools. However, so far, no shear stress studies on clonal heterogeneity have been published. We have developed a novel bioassay system to study several shear stress conditions in parallel on clonal expanded single cells. The device consists of a silicon/glass microwell slide with integrated polydimethylsiloxane microchannels, which delivers shear stress to cells in a well-controlled manner using micropumps. The flow behavior of the device was numerically characterized by computational fluid dynamics analysis, which confirmed that the desired fluid-imposed shear stress was obtained. Bovine aortic endothelial cells were cultured in the microwells for 24 hours and then subjected to a fluid shear stress of up to 2.0 Pa for 6 hours. The results showed that alignment and elongation of the endothelial cells along the flow direction were dependent on the level of shear stress applied. It was demonstrated that multiple experimental conditions can be examined simultaneously within a single device and the compartmentalized structure of the microwell slide can be used to ensure physical separation of cells in individual wells. Moreover, it was shown that the device could reduce consumption of expensive reagents and enable screening of rare samples.

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During embryogenesis, human hematopoietic stem cells (HSCs) first emerge in the aorta-gonad-mesonephros (AGM) region via transformation of specialized hemogenic endothelial (HE) cells into premature HSC precursors. This process is termed endothelial-to-hematopoietic transition (EHT), in which the HE cells undergo drastic functional and morphological changes from flat, anchorage-dependent endothelial cells to free-floating round hematopoietic cells. Despite its essential role in human HSC development, molecular mechanisms underlying the EHT are largely unknown. This is due to lack of methods to visualize the emergence of human HSC precursors in real time in contrast to mouse and other model organisms. In this study, by inducing HE from human pluripotent stem cells in feeder-free monolayer cultures, we achieved real-time observation of the human EHT in vitro. By continuous observation and single-cell tracking in the culture, it was possible to visualize a process that a single endothelial cell gives rise to a hematopoietic cell and subsequently form a hematopoietic-cell cluster. The EHT was also confirmed by a drastic HE-to-HSC switching in molecular marker expressions. Notably, HSC precursor emergence was not linked to asymmetric cell division, whereas the hematopoietic cell cluster was formed through proliferation and assembling of the floating cells after the EHT. These results reveal unappreciated dynamics in the human EHT, and we anticipate that our human EHT model in vitro will provide an opportunity to improve our understanding of the human HSC development.

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造血幹細胞は自己複製能と多分化能を持ち，その運命選択は，しばしば，生（自己複製）と死（分化）に例えられる。幹細胞が自己複製するのか，それとも分化するのかは，環境からの刺激によって指示されるのではなく，内在性因子によって確率論的に制御されると考えられてきた。一方で，造血幹細胞は定常状態では骨髄内の特殊な微小環境（ニッチ）に存在して静止状態を維持しているのに対し，ストレス環境下では活性化して増殖・分化を行うことで，造血の維持あるいは血球産生を行っている。このことから，生体内の微小環境（ニッチ）には，幹細胞の動態をコントロールする何らかの仕組みが存在すると考えられる。また，幹細胞の自己複製と分化は，均等・不均等分裂のバランスによって調節されており，ニッチからの環境シグナルが分裂様式に影響を与えることで，幹細胞の運命決定に関わっていることも予想される。そのため幹細胞の動態制御機構の解明には，細胞外環境シグナルの機能を1細胞レベルで明らかにすることが重要な鍵となる。

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Low-income settlement is a common problem existing in many countries. By using 2012 survey data of UN-HABITAT and CASS, this paper focuses on the change of original residents' subjective happiness during the process of low-income settlement reconstruction in six cities of Liaoning province. Several conclusions are obtained: (1) Low-income settlement reconstruction had significant effects on original residents' happiness, the relation between income level and happiness exhibits an inverted-U shape after reconstruction; (2) Quantile regression estimation shows that the community life quality improvement affected positively on different happiness levels of original residents, while new communication methods and the change of neighbor relationship after reconstruction cannot improve subjective well-being; (3) According to the low-income class, the influencing factors of happiness is so different with other groups and also government's indirect pro-poor policies received slightly less positive effect. Therefore, authorities should pay more attention to both explicit and implicit effects of low-income settlement reconstruction.

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