Hot Topic: Prepubertal Ovariectomy Alters the Development of Myoepithelial Cells in the Bovine Mammary Gland

The effect of ovariectomy on myoepithelial development in prepubertal heifers. Representative micrographs of tissues from a control heifer killed at 40 d of age (panel A), intact (INT) animal at 100 d (panel B), and ovariectomized (OVX) animal at 100 d (panel C) are shown to illustrate the observed differences in basal cell morphology and smooth muscle actin (SMA) staining. Scale bars (in white) indicate 50μm. Positive SMA (SMA+) staining is visible in panels A and C but is essentially absent in panel B. Note that staining for SMA in myoepithelial cells (panel A, dark arrow) was frequently more intense than vascular SMA staining (panel A, white arrow). Panel D illustrates the quantitative assessment of SMA staining of cells in the basal stratum of parenchymal epithelia from INT (gray bars) and OVX (black bars) heifers. Each bar represents the average percentage of SMA+ cells in a given treatment group, as indicated (mean ± SE). Panel E depicts the results of our reverse transcription-PCR analysis for maspin expression. Although our present results are not quantitative, maspin expression in the prepubertal bovine mammary gland has not been previously reported, but was detected in both INT (I) and OVX (O) heifers.