Figure 1. Model scheme of the regulatory network of mESC pluripotency.

The core network (inner grey square) is composed of the TFs Oct4-Sox2, Nanog and Rex1, which are linked by positive feedback and feedforward loops (black arrows). The respective transcription rates are denoted by s_i. The extended network (outer grey square) includes FGF4/Erk signalling and a differentiation signal Y, the latter facilitating the double-negative feedback loop from Nanog on all factors of the core network. FGF4/Erk is activated by Oct4-Sox2 and represses Nanog with rate p. High Nanog levels block the transmission of differentiation signal Y. The internal part of the differentiation cascade (denoted by Y_in) negatively regulates the expression of Oct4-Sox2, Nanog and Rex1.