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.

G, Smolenski, JJ Bond, TT Wheeler, NC Roy, WC McNabb, and SA McCoard

Proceedings of the New Zealand Society of Animal Production, Volume 67, Wanaka, 407-412, 2007
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