Fig. 1.

Development of lumen-containing structures by cells cultured on EHS matrix. Isolated primary mammary epithelial cells were cultured on EHS matrix in the presence of lactogenic hormones for 3h (A), 24h (B), or 5 days (C,D), fixed, critical point dried and observed with SEM. The isolated epithelial cells are seeded as small clumps and scattered single cells that adhere rapidly to the matrix substratum by 3h (A), but do not appear to spread out on it. After 24h in culture (B), the cell clumps have attached firmly to the matrix and have apparently pulled it in toward themselves, leaving large areas of the culture dish cleared. By 4–6 days in culture (C), most of the cells are present in spheroids, which are completely surrounded by matrix. At higher magnification (D), the fibrillar nature of the matrix meshwork surrounding the bracketed spheroid in C is clearly seen. (A-C) Bar, 100μm; (D) bar, 25μm.