计算机辅助共同学习

一、学生与学生之间的相互作用:易被忽视的但却有是力的学生之间怎样相互作用,是计算机辅助教学系统中被忽视的一个方面。大量的训练时间花费在帮助教师在(a)学生与计算机之间;(b)学生与课程内容之间;以及(c)教师与学生之间安排合适的相互关系,而对于使用计算机工作过程中,学生与学生之间的相互关系却相对地被忽略。应当指出:教师构造怎样的学生与学生之间相互关系的模     

Induction of alternative fate other than default neuronal fate of embryonic stem cells in a membrane-based two-chambered microbioreactor by cell-secreted BMP4

Cell-secreted soluble factor signaling in a diffusion dominant microenvironment plays an important role on early stage differentiation of pluripotent stem cells invivo. In this study, we utilized a membrane-based two-chambered microbioreactor (MB) to differentiate mouse embryonic stem cells (mESCs) in a diffusion dominant microenvironment of the top chamber while providing enough nutrient through the bottom chamber. Speculating that accumulated FGF4 in the small top chamber will augment neuronal differentiation in the MB culture, we first differentiated mESCs for 8 days by using a chemically optimized culture medium for neuronal induction. However, comparison of cellular morphology and expression of neuronal markers in the MB with that in the 6-well plate (6WP) indicated relatively lower neuronal differentiation in the MB culture. Therefore, to investigate whether microenvironment in the MB facilitates non-neuronal differentiation, we differentiated mESCs for 8 days by using chemically defined basal medium. In this case, differentiated cell morphology differed markedly between the MB and 6WP cultures: epithelial sheet-like morphology in the MB, whereas rosette morphology in the 6WP. Expression of markers from the three germ layers indicated lower neuronal but higher meso- and endo-dermal differentiation of mESCs in the MB than the 6WP culture. Moreover, among various cell-secreted soluble factors, BMP4 expression was remarkably upregulated in the MB culture. Inhibition of BMP4 signaling demonstrated that enhanced effect of upregulated BMP4 was responsible for the prominent meso- and endo-dermal differentiation in the MB. However, in the 6WP, downregulated BMP4 had a minimal influence on the differentiation behavior. Our study demonstrated utilization of a microbioreactor to modulate the effect of cell-secreted soluble factors by autoregulation and thereby inducing alternative self-capability of mESCs. Understanding and implementation of autoregulation of soluble factors similar to this study will lead to the development of robust culture systems to control ESC behavior.     

克服基因疗法的障碍

提供必需的基因不治疗疾病的方法仍然是一个令人感兴趣的想法，然而在基因疗法成为现实之前，临床与基础研究人员仍有许多工作要做。