Tcf3 and Tcf4 are essential for long-term homeostasis of skin epithelia

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Abstract
Elaine Fuchs and colleagues present mice conditionally lacking Tcf3 and Tcf4 in the skin and show that they play a role in long-term maintenance and wound repair of both epidermis and hair follicles. Single-layered embryonic skin either stratifies to form epidermis or responds to Wnt signaling (stabilized β-catenin) to form hair follicles. Postnatally, stem cells continue to differentially use Wnt signaling in long-term tissue homeostasis. We have discovered that embryonic progenitor cells and postnatal hair follicle stem cells coexpress Tcf3 and Tcf4, which can act as transcriptional activators or repressors. Using loss-of-function studies and transcriptional analyses, we uncovered consequences to the absence of Tcf3 and Tcf4 in skin that only partially overlap with those caused by β-catenin deficiency. We established roles for Tcf3 and Tcf4 in long-term maintenance and wound repair of both epidermis and hair follicles, suggesting that Tcf proteins have both Wnt-dependent and Wnt-independent roles in lineage determination.