Fig. 6.

Myoepithelial cells are present early in postnatal development but do not contribute to other epithelial lineages in the lacrimal gland. (A) Imaging of myoepithelial cell emergence. ACTA2 protein was not observed at P0 (a), but was detected by P3 (b) in rounded cells within the acini bordering the mesenchyme. Myoepithelial cells began to emerge from the columnar epithelium by P5 (c). By P7 (d), these cells began to radiate processes, assuming their stellate mature appearance by P10 (e), which was maintained in adult glands (f). Arrowheads mark processes. Scale bar: 25 μm. (B) KRT5 (a) and P63 (b) were expressed at P1 in cells of acini immediately adjacent to the mesenchyme. P63⁺ cells also expressed SOX10 (c). High-magnification image in d (from boxed region in c) confirmed co-expression of these two markers Scale bars: 100 μm in a-c; 25 μm in d. (C) By P4, SOX10⁺ cells at the border of acini co-expressed ACTA2 (a) and P63 (b). Likewise in adult lacrimal glands, ACTA2⁺ECAD⁺ myoepithelial cells remained SOX10⁺ (c) and P63⁺ (d). Arrowheads indicate positive cells. (D) Genetic lineage tracing using the Acta2 promoter indicated that myoepithelial cells do not contribute to acinar or ductal lineages. Recombination was induced by tamoxifen injection in adult Acta2^CreERT2;Rosa26^RFP mice, and cells were traced for 6 months. RFP⁺ cells co-expressed ACTA2 (a). b is a higher magnification image of the boxed area. Scale bars: 100 μm in a; 25 μm in b. Arrowhead indicates positive cells.