Fig. 7. The regulatory effect of rBM on ER levels is reproduced by purified collagen-IV and laminin-1. (A) Isolated mouse mammary epithelial organoids (a) were grown in the presence of different matrix components dripped into the medium: collagen-I (b), collagen-IV (c), laminin-1 (c) or a mixture of laminin-1 and collagen-IV (e). In all cases the organoids were attached and spread on the plastic after 2 days in culture. Bar, 100 µm. ER protein levels were measured in these different culture conditions by western blot at days 2 and 6 after culture, and expressed as relative units to levels at time 0 (f). Results are the average of four different primary culture preparations. *P<0.05 vs. plastic. (B) Scp2 cells formed monolayers after dripping collagen-I (a) or collagen-IV (b), and adopted a rounded morphology when laminin-1 was dripped into the medium (c). Bar, 100 µm. ER protein levels were determined by western blot at day 3 in culture, quantified by densitometry and were expressed relative to the values measured on plastic (d). n=5; *P<0.05.