Figure 3. Lgl1 is required for collective migration but not ductal elongation of the mammary epithelium.

(A–C) In vitro branching assay in which Lgl1^+/+ control (A) and Lgl1^Δ/Δ mutant MEC aggregates (B) were subjected to cultures in basal medium containing FGF2. When stimulated by FGF2 at progressively higher concentrations from 0.025 nM to 1 nM, a progressively higher percentage of MEC aggregates underwent branching. (C) Quantitative comparisons of control and mutant MECs in their ability to undergo epithelial branching in vitro. Data were from three independent experiments. At least 100–150 organoids were examined for each treatment condition.

(D and E) Time course of control (D–D‴) and mutant Lgl1^Kcre-KO (E–E‴) organoid migration toward beads pre-soaked in FGF10.

(F and G) Quantification of the daily (F) and total (G) displacement of control and Lgl1^Kcre-KO organoids.

(H and I) Expression of the FGF signaling target genes Etv4, Etv5, and Mkp3 in control and mutant MEC aggregates in response to 24-h treatment of FGF2 (200 ng/mL, H) or FGF10 (200 ng/mL, I). The expression is relative to that of the control samples.

Data are mean ± SD. Statistical analysis was performed using unpaired Student’s t test. *p < 0.05; **p < 0.01; ***p < 0.001; n.s., not significant.