IRX5 promotes DNA damage repair and activation of hair follicle stem cells (hfsc)

Here, we identify the transcription factor IRX5 as a promoter of HFSC activation. Irx5-/- mice display delayed onset of first postnatal anagen, with increased DNA damage and diminished HFSC proliferation. Through transcriptomic and epigenetic analysis, we discover the formation of open chromatin regions near key cell cycle progression- and DNA damage repair genes in Irx5-/- HFSC. We also identify DNA damage repair factors BRCA1 and BARD1 as IRX5 downstream targets. Inhibition of FGF18 kinase signaling partially rescues the anagen delay in Irx5-/- mice, indicating that the Irx5-/- HFSC quiescent phenotype is in part due to failure to suppress Fgf18 expression. Our findings identify IRX5 as a required promoter of DNA damage repair in HFSC activation and hair cycle initiation. Overall design: P18 and P20 back skin was dissected and incubated in 0.25% trypsin (Invitrogen 1505-065) for 2hrs at 34C. The epidermal side was mechanically separated and resuspended in 2% FBS PBS. Debris was removed with 40uM and 70uM mesh filters. Whole epidermis samples were processed for bulk RNA-seq. For HFSC bulk RNAseq, cells were labeled with CD45f (eBioscience 12-0495), Ly-6A/E (eBioscience 45-5981-82), CD34 (eBioscience 50-0341-82), and DAPI. Ly-6A/E- CD34+ CD45f+ HFSC were isolated for bulk RNAseq