Hovey R C, Davey H W, Mackenzie D D, McFadden T B
Dairy Science Group, AgResearch, Ruakura Research Centre, Hamilton, New Zealand.
Mol Cell Endocrinol. 1998 Jan 15;136(2):139-44. doi: 10.1016/s0303-7207(97)00223-2.
Although the insulin-like growth factors (IGF-I and -II) have been implicated in the stimulation of mammogenesis, little is known of their regulation in the mammary gland. In this study we removed epithelial tissue from one of the two mammary glands of 1-week-old ewe lambs and examined IGF-I and -II mRNA expression during postnatal development in both the intact mammary gland and in the gland cleared of epithelial tissue. Expression of IGF-I mRNA was highest at 6 and 10 weeks of age, coincident with the prepubertal phase of rapid mammary growth, then declined and remained low until expression increased during late pregnancy. IGF-I mRNA was more abundant in the mammary fat pad adjacent to parenchyma (MFP) than in the contralateral fat pad that had been surgically 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 generally higher levels in the intact MFP than the CFP, and in these tissues IGF-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 ovariectomy, 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 mammary parenchyma whereas estrogen suppressed levels in both the parenchyma and MFP. These findings demonstrate that IGF-I and -II mRNAs are expressed locally within the developing ovine mammary gland and are regulated by stage of ontogeny, ovarian hormones, and epithelial stromal interaction.
尽管胰岛素样生长因子（IGF-I和IGF-II）被认为与乳腺生成的刺激有关，但它们在乳腺中的调节机制却鲜为人知。在本研究中，我们从1周龄母羊羔羊的两个乳腺之一中去除上皮组织，并检查了完整乳腺和去除上皮组织的乳腺在出生后发育过程中IGF-I和IGF-II mRNA的表达情况。IGF-I mRNA的表达在6周和10周龄时最高，这与青春期前乳腺快速生长阶段一致，随后下降并保持在低水平，直到妊娠后期表达增加。与手术清除上皮的对侧脂肪垫（CFP）相比，IGF-I mRNA在与实质相邻的乳腺脂肪垫（MFP）中更为丰富。由于特定mRNA丰度的增加，实质中IGF-II mRNA的水平在1至23周龄时最高。脂肪垫中的表达较低，完整MFP中的水平通常高于CFP，并且在这些组织中，IGF-II表达在6至23周龄之间随年龄增加。我们还研究了卵巢和雌激素对IGF表达的影响。虽然IGF-I mRNA丰度不受卵巢切除术的影响，但外源性雌激素导致去卵巢母羊的MFP中表达水平更高，并倾向于增加完整母羊实质中的表达水平。卵巢切除术增加了乳腺实质内的IGF-II mRNA，而雌激素抑制了实质和MFP中的水平。这些发现表明，IGF-I和IGF-II mRNA在发育中的绵羊乳腺内局部表达，并受个体发育阶段、卵巢激素和上皮-基质相互作用的调节。
