Myoepithelial cell differentiation markers in prepubertal bovine mammary gland: effect of ovariectomy.

We reported previously that ovariectomy alters prepubertal development of mammary myoepithelial cells (MC) by mechanisms that are not well understood. Therefore, in the present study, we analyzed expression of 2 myoepithelial differentiation markers, α-smooth muscle actin (SMA) and the common acute lymphoblastic leukemia antigen (CD10), in mammary parenchymal tissue from intact (INT) and ovariectomized (OVX) heifers. On d 40, Holstein heifers underwent either an ovariectomy (OVX; n=16) or a sham (INT; n=21) operation. At 55, 70, 85, 100, 130, and 160 d of age, tissues were collected, and multispectral imaging was used to quantify immunofluorescent staining for myoepithelial cell (MC) markers. Fluorescent intensity (FI) of the markers was normalized against a control sample. In the basal epithelial layer, CD10 FI was less and SMA FI was greater in OVX than INT. The ratio of SMA to CD10 FI, as a proxy indicator for MC differentiation, was greater in tissue from OVX compared with INT heifers after 55 d of age. The staining for SMA was frequently more intense along the basal aspect of cells, whereas CD10 expression was localized on the apical surface of the MC. In mammary tissue from both INT and OVX heifers, we observed basal cells that were negative for both CD10 and SMA, some of which appeared to span the distance from basement membrane to the ductal lumen. Interestingly, we also observed CD10+ cells adjacent to the ductal lumen, a situation that was more prevalent in OVX than in INT heifers. Also, ovariectomy affects MC expression of both SMA and CD10, as well as the pattern of MC development. Myoepithelial cells are known to limit parenchymal growth in other species. Involvement of MC as regulators of prepubertal bovine mammary development is worthy of further investigation.