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Therefore, we investigated whether we can reverse the effect of global inhibition of miRNA synthesis on p21 by specifically re-establishing expression of members of the miR-302 family. To do so, we introduced into undifferentiated hESCs miRNA mimics for all four members of the miR-302 family (miR-302s) along with the plasmids expressing anti-Ago2 and anti-Dic1 http://www.selleck.cn/products/lee011.html short hairpins. First, we quantified the expression of p21, cyclin D1, and HPRT mRNA by RT-PCR 24 hours post-transfection. HPRT served as a negative control as it is not a predicted target of miR-302s (www.targetscan.org) and cyclin D1 served as positive control (validated target for miR-302s). The data show (Supporting Information Fig. S4D) that transfection by miR-302s led to downregulation of p21 and cyclin D1 mRNA by 39% and 38%, respectively. The mRNA levels of HPRT were not changed. Subsequently, we quantified the expression of p21 on the protein level. As shown in Figure 4D and 4E, matured miRNAs of the miR-302 family rescued by approximately 50% the effect of global inhibition of miRNA synthesis on the level of p21 protein (p http://www.selleckchem.com/products/i-bet-762.html Fig. S4E, S4F), thus, confirming the data published previously [34, 35] as well as functionality of our approach. No such effect was observed in hESCs transfected with mimic negative control. Additionally, downregulation of p21 was unlikely to be due to a change in the differentiation state of hESCs, because the level of the key pluripotency regulators Oct4, Sox2, and Nanog remained unaffected (Fig. 4D) by the given miRNA mimics. Notably, the downregulation of p21 mRNA after transfection of cells by miR-302s mimics suggests that both inhibition of translation and destabilization of mRNA are the involved regulatory mechanisms. This is in concordance with the current understanding of miRNA functions reviewed in [36]. Finally, to provide evidence that miR-302s physically interact with p21 mRNA, we cotransfected primary human fibroblasts with luciferase reporter gene with 3��UTR region of p21 mRNA simultaneously with miR-302s mimic. As negative controls, we used scramble miRNA mimic and miR-34a mimic. Luciferase activity was http://www.selleckchem.com/products/epacadostat-incb024360.html inhibited by 30% (p = .005) compared with negative control transfected cells and 33% (p = .02) compared with cells transfected with miR-34a (Fig. 4F). We also show that miR-302s mimic specifically interact with 3��UTR region of p21 as no effect was detected on luciferase reporter gene with 3��UTR region of GAPDH mRNA (Fig. 4F). We thus conclude that members of the miRNA family miR-302 are specific regulators of p21 protein in undifferentiated hESCs. hESCs possess a characteristic of rapid progression through the cell cycle, which is associated with an extremely short G1 phase [7].