Organization and Growth of Mammary Epithelia in the Mammary Gland Fat Pad

Abstract

Mammary gland development consists of a series of very highly ordered events involving interactions among a number of distinct cell types. An important aspect of mammary gland development is that the mammary gland consists of a fat pad of mesodermal origin into which epithelial cells of ectodermal origin proliferate. This proliferation of epithelial cells into the mammary fat pad is the subject of this review. The nature of the stroma into which epithelial cells proliferate is of considerable importance in determining the structure of the resulting gland. In mice, white adipose tissue appears to be required for normal mammary development. Transplantation of mammary epithelia to other types of stroma does not support epithelial growth or result in abnormal growth. To date, a synthetic substratum capable of mimicking white adipose tissue has not been developed. Although collagen gel cultures are generally considered superior to glass or plastic substratum in supporting near normal epithelial growth, the technique has not advanced to the point that the in vivo growth pattern is duplicated. Recent research on the generation of chimeric mammary tissue (by transplanting mammary epithelia from rats, cows, and women to the mammary fat pads of athymic nude mice) suggests that there are important species differences in the stromal requirements for mammary gland development. In particular, extensive and expansive growth of rat mammary tissue is observed in mouse mammary fat pads. However, the mouse mammary fat pad appears incapable of supporting expansive growth of bovine or human mammary epithelia. The reason for this difference is not clear. However, human and bovine mammary epithelia may require the presence of more fibrous (collagenous) tissue than rodent mammary epithelia for normal proliferation.

Modeling tissue-specific signaling and organ function in three dimensions

“…Moreover, techniques routinely used to prepare orthotopic sites, such as irradiation, may in fact induce profound and lasting stromal effects by themselves (Barcellos-Hoff and Ravani, 2000;Barcellos-Hoff, 2001). Furthermore, human mammary epithelial cells injected into cleared fat pads do not elaborate ductal structures (Sheffield, 1988), which emphasizes the apparent incompatibility between human and mouse mammary organs.…”

In vitro multipotent differentiation and barrier function of a human mammary epithelium

“…These morphologic features interactions between stroma and epithelium in the human and mouse (Parmar and Cunha 2004). On a practical level, it has not been possible to grow and differentiate normal human mammary epithelial cells in the mouse mammary fat pad (Sheffield 1988). Recent studies have attempted to circumvent this problem by co-transplanting human stroma and epithelium in mice (Kuperwasser et al 2004;Proia and Kuperwasser 2006).…”

Mammary Stem Cell Research in Veterinary Science: An Update

“…For instance, the mammary fat pad in the postnatal mouse consists primarily of adipocytes irregularly interspersed in between the fine septa of fibroblasts and connective tissue [8,9]. In contrast, there is a much greater abundance of interlobular fibroblastic connective tissue and only a limited number of adipocytes in the bovine and human mammary fat pad [8,[10][11][12].…”