Submitted to: Joint Abstracts of the American Dairy Science and Society of Animal Science
Publication Type: Abstract only
Publication Acceptance Date: 2/20/2005
Publication Date: 7/1/2005
Citation: Annen, E.L., Gentry, P.C., Sprissler, R., Hadsell, D.L., Capuco, A.V., Collier, R.J. 2005. Effects of continuous milking (cm) and prostaglandin e2 (pge2) on mammary gene expression in dairy cows [abstract]. J. Dairy Science. 83(1):364. Interpretive Summary:
Technical Abstract: First and second lactation cows (n=8) were utilized in a half udder model in which one half was dry 60 d (CTL) and the other half CM. Udder halves (n=16) were assigned a postpartum (PT) treatment of + or ' PGE2 (875 'g), treatment by intramammary infusion at calving and 72 h PT. Tissue samples were obtained at 3 and 7 d after milk stasis of the CTL udder half and at 2 and 4 d PT. In CTL halves, MEC growth was higher at 7 d of milk stasis and apoptosis was elevated at 3 and 7 d of milk stasis. PT MEC growth was increased in CM halves, but apoptosis was similar in CM and CTL tissue. PT milk yield was reduced in CM halves. Milk yield and MEC turnover was unaffected by PGE2. RNA pools were created for prepartum (PP) and PT timepoints for each udder half. We evaluated expression of adenosine 5'-triphosphate binding cassette gene-2 (ABCG2, stem cell marker), '-lactalbumin ('-lac, lactose synthesis) bax (apoptosis), bcl2 (survival), CCAT/enhancer binding protein-ß (CEBP-ß, mammary growth); insulin-like growth factor binding protein 5 (IGFBP5, apoptosis); kinase inhibitor protein p27 (p27, cell cycle arrest). The housekeeping gene, 18S, was not changed by any of the treatments or interactions. PGE2 did not alter gene expression. Involution of PP CTL tissue was associated with decreased (P < 0.02) '-lac expression, increased expression of bax (P < 0.05) and IGFBP5 (P = 0.07) expression compared to lactating CM tissue. ABCG2, CEBP-ß, cyclin D1, p27, and bcl2 expression were not changed in CM vs. CTL tissue. In PT tissue, '-lac expression was similar in CM and CTL tissue and ABCG2 and IGFBP5 expression were increased (P < 0.05) in CTL tissue compared to CM tissue. Results demonstrate MEC apoptosis during involution of CTL tissue was regulated by bax and IGFBP5. Results for PT expression of IGFBP5 and ABCG2 warrant further investigation on the role of IGFBP5 in PP apoptosis in CTL tissue and the role of the dry period on ABCG2 expression and mammary stem cell renewal.