Dia1 is required to stabilize protrusions into the collagen matrix. (A) Time-lapse imaging in transmitted light during initiation of branching morphogenesis showing the formation and growth of protrusions in shControl and shDia1 acini over a period of 200 min. Images were obtained starting 3 h after addition of 20 ng/ml HGF. See also Video 4. (B) The proportion of acini from each cell type that formed any protrusions over 12 h of imaging with numbers of acini scored indicated below each plot. Error bars indicate SD. (C) Histogram summarizing the distribution of protrusion lifetimes from acini for each cell type from videos obtained 1 h after HGF addition. Numbers of protrusions scored are indicated in the legend. (D) Plot of maximum protrusion length reached as a function of lifetime.