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

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. We used microarray to molecularly profile basal cells isolated from the interfolliular epidermis during force-mediated tissue expansion and after 12-O-Tetradecanoylphorbol-13-acetate (TPA) tretment. Interfollicolar basal epideramal cells form the back skin were FACS sorted for the positive expression of ITGA6 and negative expression of CD34. The mice were subjected to force-mediated tissue expansion or 12-O-Tetradecanoylphorbol-13-acetate (TPA) tretment. Untreted animals were used as control. The three replicates samples for control and expanded condition at day4 (EXPD4) were from 3 different CD1 mice. The two replicates for the TPA treatment were from 2 different CD1 mice. For each sample, 300 basal cells were FACS sorted and used for RNA extraction and hybridization on Affymetrix microarrays.