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The lactating mammary gland is a prodigious protein-producing factory, but the milk protein synthesis mechanisms are not well understood. The major objective of this paper was to elucidate which genes and pathways were involved in the regulation of milk protein synthesis in the dairy goat mammary gland. Total 36 primiparous Guanzhong dairy goats were allotted in 12 groups according to their mammary development stages: days 90 and 150 of virgin, days 30, 90, and 150 of pregnancy, days 1, 10, 35, and 60 of lactation and days 3, 7, and 21 of involution (three animals per group). Mammary tissue RNA was isolated for quantitative real-time RT-PCR of four casein genes alpha-s1 casein (CSN1S1), alpha-s2 casein (CSN1S2), beta-casein (CSN2) and casein kappa (CSN3), four whey protein genes lactoglobulin (LGB), lactalbumin (LALBA), lactofarrin (LTF), and Whey acidic protein (WAP) and the genes which were potentially to regulate dairy goat milk protein synthesis at the level of transcription or translation [prolactin receptor (PRLR), AKT1, signal transducers and activators of transcription 5 (STAT5), E74-Like Factor 5 (ELF5), eukaryotic translation initiation factor 4E binding protein 1 (EIF4E-BP1), S6kinase (S6K) and caveolin 1]. The results showed that all genes were up-regulated in lactation period. The expressions of PRLR, AKT1, STAT5, ELF5, and S6K were similar to mRNA expressions of milk proteins. Our results indicated that milk protein synthesis in dairy goat mammary gland was possibly regulated by these genes.

Glucose is the major energy source for mammary epithelial cells, as well as an important substrate for lactose synthesis. Mammary epithelial cells take up glucose from extracellular fluid into the cell through glucose transporter (GLUT). This study was aimed at investigating the expression of GLUT1 glucose transporter in dairy goat mammary gland during puberty, pregnancy, lactation, and involution. Using real-time reverse transcription PCR (qRT-PCR) and Western blotting, we analyzed the expression of GLUT1 mRNA and protein in dairy goat mammary gland. GLUT1 mRNA and protein expression increased during pregnancy and lactation, especially at peak lactation, and decreased strongly after weaning. Furthermore, the location of GLUT1 protein was determined by immunofluorescence laser confocal microscopy. GLUT1 protein localised to the basal and apical plasma membrane of epithelial cells, and also in the cytoplasm. The results from this study showed that GLUT1 is expressed in the dairy goat mammary gland with the greatest expression found in mammary epithelial cells during pregnancy and lactation.Key words: Expression, glucose transporter, goat, mammary gland