%0 Journal Article
%T Key stages in mammary gland development: The mammary end bud as a motile organ
%A Lindsay Hinck
%A Gary B Silberstein
%J Breast Cancer Research
%D 2005
%I BioMed Central
%R 10.1186/bcr1331
%X The mammary gland develops in two structurally and functionally distinct phases: ductal and secretory. In the ductal phase a branched 'tree' arises as the epithelial mammary anlagen invades fatty stroma and, between parturition and adolescence, undergoes repeated dichotomous branching, creating the tubes that deliver milk to the nipple (Fig. 1a). The resulting 'open' ductal architecture permits infilling of the interductal stroma by secretory alveoli during the second phase of development initiated by pregnancy. The open mammary duct system is unique in comparison with other branched organs such as the lung and kidney, whose epithelial elements are tightly packed.As we will discuss in this review, the development of the mammary ductal tree presents fascinating and challenging problems to the developmental biologist. Beyond this, there is a true urgency to improve understanding of ductal growth because 90% or more of human mammary cancers are ductal in origin. The mammary end bud is the icon of the ductal phase of mammary development in the rodent, at one and the same time the most familiar and the most mysterious of structures. Terminal end buds are familiar in rodents as the bulbous, epithelial structures at the tips of ducts strategically located facing an open expanse of fat pad (Fig. 1a, top arrows). This location and their sensitivity to mammotrophic hormones such as estrogen and growth hormone (GH) marked them early on as the engines of ductal elongation, and their implied motility was understood to be the basis for the open architecture of the mammary ductal system [1,2]. In contrast, lateral buds develop along mature ducts and are constrained in growth by the lack of open territory (Fig. 1a, side arrow). Apart from location, the general architecture and function of terminal and lateral end buds are the same.End buds, like the ducts they give rise to, have a 'tube within a tube' structure with an outer layer of undifferentiated cap cells and inner layers of l
%U http://breast-cancer-research.com/content/7/6/245