丹羽総説では、first second thirdと順を追って、転写因子蛋白の解析の難しさを書いている。
The simulations of Dunn et al. and Goode et al. raise several questions about the functioning of TF networks. The first is how to calculate the cooperative effect of multiple TFs during the activation of super-enhancers. This could be additive, synergistic or conditional. In the case of mESC-specific super-enhancers, Oct3/4 and Sox2 could be prerequisite for mediating the functions of other TFs in either an additive or synergistic manner. It is difficult, however, to compose a rule governing such cooperation, especially considering the possible role of repressive TFs such as Tcf7l1, the nucleosome remodelling deacetylase (NuRD) complex, and Gro/TLE transcriptional co-repressors (Hnisz et al., 2013; Wray et al., 2011; Reynolds et al., 2012; Laing et al., 2015). A second question raised is how to evaluate the function of TFs as proteins, which is itself a challenge. Protein levels are regulated at translational and post-translational levels. For example, the stability and translation efficiency of Sox2 mRNA is regulated by multiple microRNAs, while the stability and activity of Sox2 protein is controlled by multiple modifications such as acetylation, phosphorylation, ubiquitylation, sumoylation and methylation (Liu et al., 2013). A third question is how to account for the complex interactions of TFs that can modulate the activity of other TFs either positively or negatively, as has been shown in the case of Sox2 and Tex10 (Ding et al., 2015).