Fig. 5

High MRTF-A activity causes luminal filling in primary mammary acini. Acinar organoids were extracted from the mammary gland of 8–12 week old female wildtype (wt) and transgenic (tg) mice carrying a LSL-MRTF-A cassette and CreERT2. Organoids were seeded on matrices with increasing stiffness and treated for 4 days with 0.25 μM Hydroxy-Tamoxifen (4OHT) or vehicle control. A Representative images of primary murine acini stained for nuclei (DAPI, blue) and actin (phalloidin, green) on matrigel/collagen I matrices 5 days after seeding. Arrowheads indicate protrusions, and asterisks the acinar lumen. B, C Distribution of individual organoid roundness and diameters. D, E Percentage of acini with filled lumen and protrusions. More than 17 acini were analysed per condition. Significance was determined by two-way ANOVA. F Genotyping of 4OHT-treated ( +) and vehicle treated ( − ) tg acini using primer flanking the loxP STOP loxP cassette (LSL, 1500 bp) in comparison to an untreated positive control sample (Ctrl). *p ≤ 0.05, **p ≤ 0.01, ***p ≤ 0.001. Error bars or whiskers, SEM. Scale bars, 25 μm