Mammary development

Abstract

The basic structure of the mammary gland is laid down in the fetus. There is an important postnatal phase of allometric development, involving duct elongation and penetration of the mammary stroma at a rate greater than increase in body size. This begins before, and in some species continues through, puberty. The mammary gland then undergoes a cycle of proliferation, differentiation, function and regression during adult reproductive life in female mammals. In eutherian mammals, development of the lobules of alveolar cells which secrete milk occurs principally during pregnancy, but growth of the gland continues into lactation, accounting for as little as 2% (sheep) or as much as 26% (goats) or 40% (rats) of total increase in DNA (see Forsyth, 1982;Tucker, 1987). The classical methodological approaches of endocrinectomy and replacement therapy have established the importance of hormones from the ovary, adrenal, pituitary gland and placenta in bringing about mammary development. More recently, in vitro methods have been devised which are suitable for the study of mammary epithelial cell proliferation, and these are revealing the influence of growth factors in controlling cell numbers. At the same time, in vivo studies emphasize the importance of nutrition in modulating mammary development. Endocrine control of postnatal mammary development:in vivo studies Mammary development requires the complex interplay of many hormones. Studies are most complete in rodents. In rats (Lyons, 1958) and in mice (Nandi, 1959) deprived of pituitary, adrenals and ovaries (triply-operated) appropriate hormone combinations will bring about the different phases of mammary development.Prepubertal growth. Allometric duct growth and end bud formation are brought about in triply-operated rodents by oestrone + adrenal corticoid + growth hormone (GH).Although beginning before puberty, allometry is abolished by ovariectomy and restored by oestrogen administration in rodents (Cowie, 1949) and in heifers (Wallace, 1953). However, in lambs, early ovariectomy influences neither mammary development nor total oestrogens in the circulation (Wallace, 1953; Johnsson, 1984). Allometric duct growth may be initiated by an interaction between ovarian hormones and GH secretion resulting from maturation of the hypothalamic-pituitary axis. In ovariectomized female rats, a crude pituitary extract was needed together with exogenous oestrogen to advance the onset of allometric duct growth before day 20 (Silver, 1953)

Estrogen upregulation of BRCA1 expression with no effect on localization

“…Specifically, the ovarian steroids estrogen and progesterone, in concert with other endocrine and autocrine factors, modulate the growth and development of breast and ovarian epithelial cells [2,3]. In normal tissue, ovarian hormones initiate morphogenesis and differentiation through cycles of cell proliferation [4]. These effects may be counterbalanced by feedback mechanisms that suppress normal and neoplastic proliferation.…”

Effect of exogenous bovine growth hormone and ovariectomy on prepubertal mammary growth, serum hormones and acute in-vitro proliferative response of mammary explants from Holstein heifers

“…Evidence of interaction between the somatotrophic axis and steroid hormones, including oestrogen, has been indi¬ cated by Breier et al (1988) and Schams et al (1988). Oestrogen is present in the circulation of heifers as early as 3 months of age, and oestrogen is known to be involved in the regulation of pubertal mammary development (Forsyth, 1989). However, oestrogen seems to be unable to stimulate growth of mammary duct cells in hypophysectomized animals without treatment with pituitary extracts or GH (Silver, 1953;Cowie et al 1966).…”

Cell interactions in initiation of mammary epithelial proliferation by oestradiol and progesterone in prepubertal heifers

“…In contrast to mice, mammary epithelial response to oestradiol in prepubertal heifers is not first exhibited after a proliferative response of stromal cells. This suggests that the cel l \ x=req-\ type interactions involved in the control of mammo-INTRODUCTION Mammary development depends on interactions among both pituitary and ovarian hormones (for review see Forsyth, 1989). In particular, duct growth is induced in rodents whose pituitary, adrenal and ovaries are removed by replacement with oestrone, glucocorticoids and growth hormone.…”