Chromatin remodeling governs postnatal maturation in dermal fibroblasts [scRNA-Seq]

Tissue stem cells preserve a certain level of potency to maintain intact tissue integrity after various injury. Postnatal dermal fibroblasts lose differentiation potential for regenerative healing that recreates normal tissue including functional hair follicles (HFs), however, their intrinsic cellular changes are not understood yet. Here, we uncover a postnatal maturation process in papillary fibroblasts (PFs) mediated by Twist2-driven chromatin and transcriptional remodeling. Within 4 days after birth, dermal PFs lost WNT transcription factors (TFs) and target gene expressions accompanied by loss of H3K27ac expression. Through single-cell transcriptomics, ATAC-seq and ChIP-seq profiling, we define a postnatal maturation trajectory of PFs, in addition to loss of regenerative trajectory, triggered by decrease of H3K27ac and chromatic accessibility. In vivo inhibition of histone deacetylation delays the postnatal chromatin remodeling and maintains developmental signaling and differentiation potential in PFs. TF motif analysis on the chromatin regions losing accessibility identifies TWIST as a potential regulator specifying these regions. Using Twist2 conditional knock-out mouse model, we unearth a postnatal role of Twist2 TF as governing the postnatal maturation process resulting in switch-off of developmental pathways after birth. Together, our findings expose a comprehensive intracellular mechanism driving postnatal maturation in dermal fibroblasts with profound implications for regenerative medicine. To define the intrinsic temporal changes in total skin cells after birth, mouse back skin was harvested and dissociated into dermal and epidermal single-cell suspension at postnatal day 0, 2 and 4 (PD0, PD2, PD4), or postnatal day 4 after intraperitoneal TSA treatment for 4 days (TPD4, 5μg/g body weight). For scRNA-seq, dermal and epidermal single-cell suspension were mixed with 1:1 ratio for each sample. All samples were processed according to Chromium Single Cell 3' Reagent Kits v3 Chemistry (10X Genomics) as per the manufacturer’s protocol. Library was sequenced using Illumina HiSeq X Ten platform (Illumina). Transcripts were mapped to the mm10 reference genome using CellRanger v4.0.0 with default reference package (10X Genomics).