Hair follicle stem cells (HFSCs) regenerate hair in response to Wnt signalling. Here, we unfold genome-wide transcriptional and chromatin landscapes of β-catenin–TCF3/4–TLE circuitry, and genetically dissect their biological roles within the native HFSC niche. We show that during HFSC quiescence, TCF3, TCF4 and TLE (Groucho) bind coordinately and transcriptionally repress Wnt target genes. We also show that β-catenin is dispensable for HFSC viability, and that if TCF3/4 levels are sufficiently reduced, it is dispensable for proliferation. However, β-catenin is essential to activate genes that launch hair follicle fate and suppress sebocyte fate determination. TCF3/4 deficiency mimics Wnt–β-catenin-dependent activation of these hair follicle fate targets; TCF3 overexpression parallels their TLE4-dependent suppression. Our studies unveil TCF3/4–TLE histone deacetylases as a repressive rheostat, whose action can be relieved by Wnt–β-catenin signalling. When TCF3/4 and TLE levels are high, HFSCs can maintain stemness, but remain quiescent. When these levels drop or when Wnt–β-catenin levels rise, this balance is shifted and hair regeneration initiates.

Induced pluripotent stem cells (iPSCs) with potential for therapeutic applications can be derived from somatic cells via ectopic expression of a set of limited and defined transcription factors. However, due to risks of random integration of the reprogramming transgenes into the host genome, the low efficiency of the process, and the potential risk of virally induced tumorigenicity, alternative methods have been developed to generate pluripotent cells using nonintegrating systems, albeit with limited success. Here, we show that c-KIT+ human first-trimester amniotic fluid stem cells (AFSCs) can be fully reprogrammed to pluripotency without ectopic factors, by culture on Matrigel in human embryonic stem cell (hESC) medium supplemented with the histone deacetylase inhibitor (HDACi) valproic acid (VPA). The cells share 82% transcriptome identity with hESCs and are capable of forming embryoid bodies (EBs) in vitro and teratomas in vivo. After long-term expansion, they maintain genetic stability, protein level expression of key pluripotency factors, high cell-division kinetics, telomerase activity, repression of X-inactivation, and capacity to differentiate into lineages of the three germ layers, such as definitive endoderm, hepatocytes, bone, fat, cartilage, neurons, and oligodendrocytes. We conclude that AFSC can be utilized for cell banking of patient-specific pluripotent cells for potential applications in allogeneic cellular replacement therapies, pharmaceutical screening, and disease modeling.

Immune sensor proteins are critical to the function of the human innate immune system. The full repertoire of cognate triggers for human immune sensors is not fully understood. Here, we report that human NLRP1 is activated by 3C proteases (3Cpros) of enteroviruses, such as human rhinovirus (HRV). 3Cpros directly cleave human NLRP1 at a single site between Glu130 and Gly131. This cleavage triggers N-glycine–mediated degradation of the autoinhibitory NLRP1 N-terminal fragment via the cullinZER1/ZYG11B complex, which liberates the activating C-terminal fragment. Infection of primary human airway epithelial cells by live human HRV triggers NLRP1-dependent inflammasome activation and IL-18 secretion. Our findings establish 3Cpros as a pathogen-derived trigger for the human NLRP1 inflammasome and suggest that NLRP1 may contribute to inflammatory diseases of the airway.