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com). Olympuse FluoView, Leica LAS AF6000 and Volocity 4.1 (Improvision) softwares were used for image processing, deconvolution, and quantitative imaging analyses wherever appropriate. Confocal images acquired under the identical exposure time and instrument settings among different groups were used for colocalization and quantitative fluorescence intensity analyses. Time-lapse live-cell imaging is described in the Supporting Information Methods. Results are expressed as mean �� Standard Deviation (SD). Statistical significance was determined using a Student's t test, ANOVA, or ��2 wherever appropriate. Results were considered significant when p http://www.selleckchem.com/products/MG132.html localization in hESCs to assess the function of Rap1 in regulating the self-renewal of hESCs. Using a well-established pull-down method [14], we identified the expression of both total Rap1 and active Rap1 (GTP-bound Rap1) in undifferentiated hESCs (Fig. 1A). These undifferentiated hESCs were characterized by the expression of Nanog, Oct4, SSEA4, Tra-1-60, Tra-1-81, and AP, and the capacity to form teratoma (Fig. 1B and data not shown). Consistent with previous findings in epithelial cells [13, http://www.selleck.cn/products/pfi-2.html 14], we observed that Rap1 in undifferentiated hESCs was localized to the plasma membrane and the perinuclear region (Fig. 1C, GFP-Rap1-transfected hESCs; Supporting Information Fig. 1, immunocytochemical staining). The presence of Rap1 protein in hESCs prompted us to explore whether Rap1 plays an important role in the self-renewal of hESCs. We suppressed Rap1 function by treating hESCs with GGTI-298. GGTI-298 specifically inhibits Rap1 but not Ras and has been well-characterized and used in numerous studies of Rap1 signaling [39�C43]. Treatment of hESCs with GGTI-298 led to a significant reduction in Rap1 protein levels (Fig. 1D), and resulted in a decrease in the number of undifferentiated colonies as indicated by AP activity (Fig. 1E). AP activity was closely associated with the expression of Nanog and Oct4 (Fig. 1B), and has been used as a sensitive and reliable marker for undifferentiated hESCs [44�C46]. Collectively, these results suggest that http://www.selleckchem.com/products/epacadostat-incb024360.html Rap1 is required for the maintenance of hESCs in an undifferentiated state. Using a novel clonogenic assay based on a primary and secondary plating strategy [37, 44, 47], we further examined the role of Rap1 in the self-renewal of hESCs. In the assay, hESCs treated with the Rap1 inhibitor exhibited a marked decrease in clonogenic capacity and self-renewal potential (Fig. 2A) and an increase in cell deaths (unpublished observations). In contrast, vehicle-treated hESCs formed typical colonies and maintained self-renewal capacity (Fig. 2A). These results demonstrate that Rap1 plays an important role in hESC self-renewal. To validate the findings from GGTI-298 Rap1 inhibitor, we analyzed the effects of Rap1 siRNA knockdown on hESC self-renewal.