Growth of mouse mammary gland end buds cultured in a collagen gel matrix

A method was developed for isolating end buds as a pure subpopulation from collagenase and hyaluronidase digested 4-week-old C57BL/Crgl mouse mammary glands, and the end buds showed the greatest growth response to media, including equine serum and cholera toxin.

Abstract

End buds are the growing terminal structures of the ducts in the mammary gland. They are made up of undifferentiated epithelial cells that, under the hormonal milieu of adult and pregnant females, give rise to the ducts and alveoli of the mature gland. The end buds are of interest in understanding the developmental biology of the gland. They are also likely targets for many mammary carcinogens and, therefore, of interest in understanding the biology of mammary cancer. A method was developed for isolating end buds as a pure subpopulation from collagenase and hyaluronidase digested 4-week-old C57BL/Crgl mouse mammary glands. They were cultured within a rat tail collagen gel matrix for 3 weeks and fed with media containing various combinations of sera, hormones and growth-promoting factors. Growth in response to the different media was measured by photographing individual end bud colonies over time using dark field illumination. The growth of the individual colonies was quantitated using a computer-assisted photodensitometry method of determining the colonies' mass. The end buds showed the greatest growth response (greater than 20-fold increase in 3 weeks with a minimum doubling time of 48 h) to medium supplemented with 50% equine serum and cholera toxin or with less serum (15%) and epidermal growth factor (EGF), hormones and cholera toxin. Initially, the colonies grew logarithmically, then slowed as the colony size increased. This was due, in part, to the cessation of growth by the cells in the center. This end bud culture system differs from that of dissociated mouse mammary cells in a number of ways which are discussed.