MORPHOGENESIS AND SECRETORY ACTIVITY OF MOUSE MAMMARY CULTURES ON EHS BIOMATRIX

The nature of the substratum profoundly influences the growth and function of epithelia in tissue culture. "Mammospheres", hollow spherical structures, develop when epithelial clusters are plated on a biomatrix derived from the Engelbreth-Holm-Swarm murine tumour (EHS matrix). Morphologic examination of mammosphere development demonstrates that morphogenesis is a two stage process. Over the first 48 h the cells aggregate into spheres, drawing the matrix up and over themselves to become buried within the material. Changes in matrix morphology emphasize the importance of the quasi-fluid nature of the substratum on which the cells are plated. Lumen formation ensues over the next 2 to 5 days as the cells, polarized by basal contact with the matrix, differentiate. They form tight junctions at their apical borders and synthesize milk proteins, secreting caseins into the enlarging interior cavity and transferrin from their basal surfaces into the medium. These experiments demonstrate that the physical properties of the EHS matrix allow epithelial cells to develop the cuboidal shape necessary for secretory activity.