Embryonic Mammary Gland Development; a Domain of Fundamental Research with High Relevance for Breast Cancer Research

Abstract

Mammary gland development is often presented as a series of events happening during puberty, pregnancy, lactation and involution; even though it starts in utero, and extensive morphogenetic events occur prior to birth. During the last century, research on the embryonic phase of mammary gland development received little attention as lactation and breast cancer investigations experienced greater emphasis. Nonetheless, important contributions were made during the 1950’s–1980’s by Boris Balinsky, Albert Raynaud, Alain Propper, Klaus Kratochwil and Teruyo Sakakura and respective coworkers in understanding mammary development in rabbit and mouse embryos. In part due to interests in developmental biology and birth defects per se, and in part due to the recognition of mechanistic parallels between organogenesis and carcinogenesis, the prenatal phase of mammary gland development has become more intensively studied again over the past decade. We set out to assemble this issue in such a way that it could serve as a textbook of prenatal mammary gland development, bringing together the older literature with the more recent insights. Though we succeeded in doing that for mammary development in mouse and rabbit embryos, admittedly and regrettably, this issue underrepresents insights in prenatal mammary development in monotremes, marsupials, and placentals other than mice and rabbit, including human. This is in part due to these species being less available for study, although interesting work has been and is currently being done on them. For a comprehensive review on progress in research on human breast development, we recommend a recent publication elsewhere by Gusterson and Stein [1]. We have been very fortunate in receiving the enthusiastic cooperation of many authors who have all greatly contributed to our current understanding of prenatal mammary gland development. We are particularly indebted to several esteemed Emeritus Professors, whom despite their “officially retired” status, generously dedicated their time and treasures of knowledge to this special issue. These scientists performed classical experimental embryology several decades ago and produced insights that are seminal to our current understanding of embryonic mammary development. Among them are Alain Propper who, using rabbit embryos as a model, was the first to demonstrate that the inductive signals for mammary gland development reside in the dermis (1967), and to propose that ‘wandering cells’ along the mammary line contribute to growth of the mammary rudiments (1978). He joined us in co-authoring a review of morphogenesis of the embryonic mammary gland in rabbit and mouse embryos, which also serves as an introduction of developmental stages and nomenclature used in other reviews in this issue. Evolutionary biologist Olav Oftedal and developmental biologist Danielle Dhouailly teamed up especially for this occasion. Olav received the inspiration to study the evolution of the mammary gland and lactation biology from the longest and perhaps least known research efforts (1890–1922) of his lineal ancestor Alexander Graham Bell to selectively (and successfully) breed sheep for increased teat number. Danielle was a naturalist at a very young age and dedicated her career to understanding skin appendage and pattern B. A. Howard (*) Division of Breast Cancer Research, Breakthrough Breast Cancer Research Centre, The Institute of Cancer Research, 237 Fulham Road, London SW3 6JB, UK e-mail: beatrice.howard@icr.ac.uk