Expression And Roles Of Insulin-Like Growth Factor Family In Mouse Mammary Gland

Postnatal mammary gland development was divided into a few stages, including virgin, pregnancy, lactation and involution, during which the mammary gland exhibited significant structural and functional changes, especially in the mammary essential tissue and adipose tissue. Adipose tissue as a necessary part of the mammary gland promoted the mammary essential tissue development by paracrine not only supporting the mammary gland structure. In the same way the growth factors producted or secreted by the mammary essential tissue reacted on adipose tissue development. Insulin-like growth factor family consisted of insulin-like growth factors(IGFs), insulin-like growth factor receptor(IGFR) and insulin-like growth factor binding proteins(IGFBPs). They played a vital role on both tissues during the mammary gland development. With the key role of IGF family in regulation of mammary gland development and lactation, to work over more details of the expression and roles of its members would contribute to elucidate their action mechanisms. To increase milk production of dairy animal has important theoretical and practical significance by regulating mammary gland development and function and maintaining mammary gland health.In this research, some timepoints were set in all stages of normal mouse mammary gland development Staining results for adipose tissue revealed that adipose tissue varied evidently in virgin, pregnant and involuting mammary gland; in virgin, adipocytes distributed around ductal tree, and some of them differentiated into preadipocytes; in pregnancy, mammary essential tissue turned into main componet of the mammary gland instead of adipose tissue; in involution, preadipocytes redifferentiate into large adipocytes, and adipose tissue represent for the main componet of the mammary gland again. Double staining mammary tissue slices by indirect immunofluorescence was examined using a laser scanning confocal microscope. The assay results of localization and quantification of IGFs, IGF-IR, IGFBPs, PAI-1 and cyclin D1 revealed that: (1) IGF-I distributed in their cytoplasm of ductal and alveolar epithelial cell, and adipocytes, also in matrix, predominantly expressed in virgin and early pregnancy, so it played a virtal role on ductal development in virgin and lobuloalveolar morphogenesis in early pregnancy, and was useful to maintain lactation; (2) IGF-II specially expressed on basal membrane side of ductal and alveolar epithelial cells; IGF-II played a key positive role on ductal morphogenesis, especially a prominent role on lobuloalveolar morphogenesis and differentiation in pregnant mammary gland. The high level IGF-II expression in lactating mammary gland also appeared to be critical for initiating...