Changes in dermal cell proliferation and collagen deposition in human skin. (G) Immunofluorescence staining for Vimentin (red) and Ki67 (green) of back skin at indicated time points (upper panel). Polarised light image of Picrosirius red stained back skin section shown as binary image at indicated time points (lower panel). (H) Quantification of proliferating cells in the upper and lower dermis (n=3 biological replicates per time point). (I) Quantification of dermal cell proliferation (Ki67+) (left) and collagen density (right) with age (n= 3 biological replicates per time point). Note that cells in upper human dermis were more proliferative than cells in the lower dermis at all developmental time points analysed and that fibroblasts entered a quiescent, non-proliferative state before collagen was efficiently deposited. Data shown are means ±s.d. Nuclei were labelled with DAPI (blue in B,E,G). Scale bars, 100µm. wk, week. 