Vasculature-driven stem cell population coordinates tissue scaling in dynamic organs.

Stem cell (SC) proliferation and differentiation organize tissue homeostasis. However, how SCs regulate coordinate tissue scaling in dynamic organs remain unknown. Here, we delineate SC regulations in dynamic skin. We found that interfollicular epidermal SCs (IFESCs) shape basal epidermal proliferating clusters (EPCs) in expanding abdominal epidermis of pregnant mice and proliferating plantar epidermis. EPCs consist of IFESC-derived Tbx3+-basal cells (Tbx3+-BCs) and their neighboring cells where Adam8-extracellular signal-regulated kinase signaling is activated. Clonal lineage tracing revealed that Tbx3+-BC clones emerge in the abdominal epidermis during pregnancy, followed by differentiation after parturition. In the plantar epidermis, Tbx3+-BCs are sustained as long-lived SCs to maintain EPCs invariably. We showed that Tbx3+-BCs are vasculature-dependent IFESCs and identified mechanical stretch as an external cue for the vasculature-driven EPC formation. Our results uncover vasculature-mediated IFESC regulations, which explain how the epidermis adjusts its size in orchestration with dermal constituents in dynamic skin.

Tbx3-dependent amplifying stem cell progeny drives interfollicular epidermal expansion during pregnancy and regeneration.

The skin surface area varies flexibly in response to body shape changes. Skin homeostasis is maintained by stem cells residing in the basal layer of the interfollicular epidermis. However, how the interfollicular epidermal stem cells response to physiological body shape changes remains elusive. Here, we identify a highly proliferative interfollicular epidermal basal cell population in the rapidly expanding abdominal skin of pregnant mice. These cells express Tbx3 that is necessary for their propagation to drive skin expansion. The Tbx3+ basal cells are generated from Axin2+ interfollicular epidermal stem cells through planar-oriented asymmetric or symmetric cell divisions, and express transit-amplifying cell marker CD71. This biased division of Axin2+ interfollicular epidermal stem cells is induced by Sfrp1 and Igfbp2 proteins secreted from dermal cells. The Tbx3+ basal cells promote wound repair, which is enhanced by Sfrp1 and Igfbp2. This study elucidates the interfollicular epidermal stem cell/progeny organisation during pregnancy and suggests its application in regenerative medicine.The abdominal skin expands rapidly during pregnancy. Here the authors show that a population of highly proliferative stem cell progenies expressing the transcription factor Tbx3 is required for abdominal skin expansion in pregnant mice.

Essential roles of Tbx3 in embryonic skin development during epidermal stratification.

Stepwise differentiation of epidermal cells is essential for development of stratified epithelium, but the underlying mechanisms remain unclear. Here, we show that Tbx3, a member of the T-box family of transcription factors, plays a pivotal role in this mechanism. Tbx3 is expressed in both basal and suprabasal cells in the interfollicular epidermis of mouse embryos. Epidermis-specific Tbx3 conditional knockout (cKO) embryos are small in size and display a thinner epidermis with an impaired barrier function. In the Tbx3 cKO epidermis, keratin 5-positive undifferentiated cells, which reside in both basal and suprabasal layers of wild-type embryos, are localized exclusively in the basal layer. In addition, mRNA expression levels of granular cell markers are increased in the Tbx3 cKO epidermis, suggesting that Tbx3 prevents premature differentiation of spinous cells. We further show that Tbx3 maintains the proliferative potential of basal cells and ensures their planar-oriented cell division. Moreover, Tbx3 is shown to be required for the expression of Hes1, a well-known Notch signaling target protein that is essential for epidermal development. We therefore propose that Tbx3 functions upstream of Hes1 to regulate proliferation and differentiation of basal and suprabasal cells during epidermal development.