Fig. 1: Single cell RNA sequencing of pubertal mammary fibroblasts.

a A representative image of a pubertal mammary gland from a 5-week-old female mouse. Scale bar: 1 cm. b Histological sections of an epithelial ducts, a terminal end bud (TEB) and a fat pad region. Scale bar: 100 µm. The asterisks mark the lumen of the epithelial compartment. c Lineage-tracing of fibroblasts in a 5-week-old Col1a2-CreERT;R26-mTmG female, 24 h after tamoxifen administration. Fibroblasts are detected as GFP+ cells around ducts, TEBs and in the fat pad. Scale bar: 100 µm. d Immunostaining for αSMA (in white) in a cleared whole-mount mammary gland detects fibroblasts around a TEB (the TEB borders are delineated by a red line) as well as cap cells of the TEBs. The top and middle optical sections of the imaged z-stack are presented; their localization according to the TEB is indicated by a green line. The full z-stack is presented in Supplementary Movie 1. Scale bars: 100 µm, 50 µm in detail (magnifications of the boxed areas). The asterisk marks the epithelium. a–d The images are representative of at least 3 biological replicates. e UMAP representation of sequenced mammary fibroblasts showing the different fibroblast clusters. f Transcriptomic scores of fibroblasts from developing fat pads³² plotted over our dataset of mammary fibroblasts. g Annotation of fibroblast clusters. h UMAPs showing expression of cluster marker genes. i, j Dot plots showing the expression of contractility-related genes (i) and genes encoding ECM components (j) within the different cell clusters identified.