question: What is the difference in the roles of Tcf1 and Tcf3 during development?
answer: Τhere are opposing effects of Tcf3 and Tcf1 in the control of Wnt stimulation of embryonic stem cell self-renewal. In contrast to β-catenin-dependent functions described for Tcf1 the known embryonic functions for Tcf3 are consistent with β-catenin-independent repressor activity. Wnt signal stimulation reduces the level of Tcf3, and increases those of Tcf1 (also known as Tcf7) and Lef1, positive mediators of Wnt signaling.