The molecular mechanisms that regulate milk protein synthesis in the dairy cow are not well understood. We used a proteomic approach to identify potential regulators of milk protein synthesis among the endoplasmic reticulum (ER) proteins. Mammary tissue was collected from mid-lactation dairy cows treated with atropine (Atr; decreased milk production), growthhormone (GH; increased milk production) or vehicle alone. Fractions enriched for ER associated proteins were prepared by differential centrifugation and then resolved by 2-dimensional electrophoresis (2-DE). Proteins were visualised using colloidal coomassie G-250 and the phosphor-protein specific stain, Pro-Q Diamond. We identified 4 significant (P<0.05) and 9 marginally significant (P<0.15) spots that were differentially expressed between treatment groups. Six spots were subjected to LTQ ion trap tandem mass spectrometry and 2 proteins were identified with a high level of confidence: major vault protein (MVP) (27% of the control level after GH treatment, P<0.05), and heat shock 70Kda protein 8 (HSPA8) (41% of the control level after Atr treatment, P <0.01). Western blotting showed a 24% decrease in HSPA8 following Atr treatment (P<0.10) and a 55% decrease in MVP following GH treatment (P<0.10). These results provide a focus for further investigation of the role of MVP and HSPA8 in influencing milk production.
Proceedings of the New Zealand Society of Animal Production, Volume 67, Wanaka, 407-412, 2007
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