Live-cell video microscopy of BC morphogenesis in LifeAct-EGFP–expressing cells. (a) A single polarizing differentiating hepatoblast forming multiple tubular lumina. Scale bar: 10 µm. See also Video 2. (b) BC network forms between neighboring cells by fusion and branching (star) of elongated tubular lumina. Scale bar: 10 µm. See also Video 3. (c) A lumen formed between two cells starts growing spherically, but is later adjusted and continues to elongate as a typical BC lumen. Scale bar: 10 µm. See also Video 4.