Figure 2.

α-Smooth muscle actin (ACTA2)-Cre^ERT2 lineage tracing of myoepithelial cells during submucosal gland development. (A) Myoepithelial cell lineage tracing timeline. Newborn ACTA2-Cre^ERT2:ROSA-TG mice were treated with a single injection of tamoxifen (0.2 mg) on the day of birth, and mice were then harvested on 3, 5, 7, and 21 days of age. (B–E) Representative photomicrographs show GFP and tdTomato expression in trachea sections at the indicated ages. DAPI was used to mark nuclei. Boxed regions (i–viii) are enlarged below the main panels. (F–I) Representative images are shown for the various phases of gland development, including (F) placode phase (phase 1), (G) elongation phase (phase 2), (H) branching phase (phase 3), and (I) differentiation phase (phase 4). Two different stages of the elongation phase are shown in (G), depicting a GFP-negative early-stage (left) and GFP-positive later-stage (right) tubule based on size. (J) Schematic diagram of the various phases of gland development shown in (F–I). Green cells mark lineage contribution observed using the ACTA2-Cre^ERT2 driver. Scale bars: B–E, 50 μm; F–I, 25 μm.