Mechanisms of stretch-mediated skin expansion at single cell resolution [ATAC-seq]

The ability of the skin to expand in response to stretching has, for decades, been exploited in reconstructive surgery. Several studies have investigated the response of stretching epidermal cells in vitro. However, it remains unclear how mechanical forces affect epidermal stem cell behaviour in vivo. Here, we develop a mouse model in which the temporal consequences of the stretching the skin epidermis can be studied. Using a multidisciplinary approach that combines clonal analysis and mathematical modelling, we show that mechanical force induces skin expansion by promoting the renewal of epidermal stem cells. This occurs through a structured response in which cell fates are coordinated locally by stem cells that switch between states primed for renewal or differentiation. Transcriptional and chromatin profiling identifies the gene regulatory networks modulated by mechanical force. Using a combination of pharmacological inhibition and several conditional gene loss-of-function mouse mutants, we dissect the signalling pathways that control force-mediated tissue expansion. Overall design: We used ATACseq to profile the chromatin landscape of basal cells isolated from the interfolliular epidermis during force-mediated tissue expansion. Interfollicolar basal epideramal cells form the back skin were FACS sorted for the positive expression of ITGA6 and negative expression of CD34. One CD1 mouse was subjected to force-mediated tissue expansion and an untreted animal was used as control. For each sample, 10000 basal cells were FACS sorted and used for ATAC preparation.