Rc. Hovey et al., ONTOGENY AND EPITHELIAL-STROMAL INTERACTIONS REGULATE IGF EXPRESSION IN THE OVINE MAMMARY-GLAND, Molecular and cellular endocrinology, 136(2), 1998, pp. 139-144
Although the insulin-like growth factors (IGF-I and -II) have been imp
licated in the stimulation of mammogenesis, little is known of their r
egulation in the mammary gland. In this study we removed epithelial ti
ssue from one of the two mammary glands of 1-week-old ewe lambs and ex
amined IGF-I and -II mRNA expression during postnatal development in b
oth the intact mammary gland and in the gland cleared of epithelial ti
ssue. Expression of IGF-I mRNA was highest at 6 and 10 weeks of age, c
oincident with the prepubertal phase of rapid mammary growth, then dec
lined and remained low until expression increased during late pregnanc
y. IGF-I mRNA was more abundant in the mammary fat pad adjacent to par
enchyma (MFP) than in the contralateral fat pad that had been surgical
ly cleared of epithelium (CFP). The level of IGF-II mRNA in parenchyma
was highest at 1-23 weeks of age due to an increase in the abundance
of specific mRNAs. Expression was lower in the fat pads, with generall
y higher levels in the intact MFP than the CFP, and in these tissues I
GF-II expression was shown to increase with age between 6 and 23 weeks
. We also investigated the influence of the ovary and estrogen on the
expression of IGFs. While IGF-I mRNA abundance was unaffected by ovari
ectomy, exogenous estrogen resulted in higher levels of expression in
the MFP of ovariectomized ewes and tended to increase its level in the
parenchyma of intact ewes. Ovariectomy increased IGF-II mRNA within m
ammary parenchyma whereas estrogen suppressed levels in both the paren
chyma and MFP. These findings demonstrate that IGF-I and -II mRNAs are
expressed locally within the developing ovine mammary gland and are r
egulated by stage of ontogeny, ovarian hormones, and epithelial-stroma
l interaction. (C) 1998 Elsevier Science Ireland Ltd.