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Exogenous TGF-ß1 Promotes Stromal Development in the Heifer Mammary Gland

Department of Animal Science, University of Vermont, Burlington 05405

Corresponding author: K. Plaut; e-mail: Karen.Plaut{at}uvm.edu.

The objectives of this study were to determine the local effects of transforming growth factor-ß1 (TGF-ß1) on mammary epithelial and stromal cell proliferation and expression of the TGF-ß1 responsive genes c-myc and fibronectin. A single slow-release plastic pellet containing 5 µg of TGF-ß1 and 20 mg of BSA was implanted in the parenchyma of the right rear quarter of the mammary gland of 9-mo-old prepubertal heifers. A control pellet containing 20 mg of BSA was implanted in the left rear quarter of each heifer. All heifers were treated with bromodeoxyuridine (BrdU) at 4, 12.5, and 22 h after the pellets were implanted to label proliferating cells. Two hours after the last BrdU injection, the animals were euthanatized, and their mammary glands were recovered. Proliferation of mammary stromal cells was significantly higher in TGF-ß1-treated quarters than in BSA-treated, control quarters (3.5 vs. 1.8% BrdU-positive cells). This result coincided with a lack of significant effect of TGF-ß1 on proliferation of mammary epithelial cells and apoptosis. By quantitative reverse transcriptase-polymerase chain reaction, we found that c-myc gene expression was unchanged after TGF-ß1 treatment, but fibronectin gene expression was increased 3-fold in TGF-ß1-treated quarters compared with BSA-treated, control quarters. Thus, we concluded that TGF-ß1 selectively acts on the stromal compartment of the bovine mammary gland by increasing cell proliferation and gene expression of the extracellular matrix protein fibronectin.

Key Words: slow release pellet • transforming growth factor-ß • mammary gland development

Abbreviation key: BrdU = bromodeoxyuridine, ECM = extracellular matrix, GAPDH = glyceraldehyde 3-phosphate dehydrogenase, TGF-ß1 = transforming growth factor-ß1, TdT = terminal deoxynucleotidyltransferase, TUNEL = terminal deoxynucleotidyltransferase-mediated dUTP nick-end labeling

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