Single Cell RNA-sequencing of murine back skin interfollicular epidermis basal cells

The ability of the skin to grow in response to stretching has, for decades, been exploited in reconstructive surgery. The response of epidermal cells to stretching has been studied in vitro. However, it remains unclear how mechanical forces affect epidermal cell behaviour in vivo. Here, we develop a mouse model in which the consequences of stretching on skin epidermis can be studied. Using a multidisciplinary approach that combines clonal analysis with quantitative modelling and single-cell RNA-seq, we show that stretching induces skin expansion by a transient bias in the renewal activity of epidermal stem cells, while a second subpopulation of basal progenitors remains committed to differentiation. Transcriptional and chromatin profiling identifies how cell states and gene regulatory networks are modulated by stretching. Using pharmacological inhibitors and mouse mutants, we define the mechanisms that control stretch-mediated tissue expansion. Overall design: The purpose of this study was to define, at the single cell level, the transcriptional profile of murine dorsal epidermal basal cells during homeostasis in adult animals, during tissue stretching at day (D)1 (EXPD1) and D4 (EXPD4) and upon 12-O-Tetradecanoylphorbol-13-acetate (TPA) tretment. Tissue stretching was performed using self-inflating hydrogels purchased from the company Osmed. The analysis was performed on CD1 mice and on basal interfollicular epidermal cells that were FACS sorted for the positive expression of ITGA6 and negative expression of CD34. Additionally, mice in stretching at D2 (EXPD2) and treated with the MEK1/2 inhibitor Trametinib and with the MAL inhibitor CCG203971 were also analysed.