Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: 2/28/2012
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: Myoepithelial cells (MC) have roles in cell proliferation and differentiation and hence, may impact mammary parenchymal morphogenesis. Because MC can limit parenchymal growth in other species, it is important to understand MC-related mechanisms involved in early bovine mammary development. We previously saw changes in expression of the nuclear marker transformation-related protein 63 (P63) and the cytoplasmic marker common acute lymphoblastic leukemia antigen (CD10), corresponding with changes in the pattern of MC development in prepubertal heifers between 40 and 160d of age. In this study, we investigated the ontogeny of MC development during the pre-weaning period by tracking the expression of these markers. Neonatal Holstein heifers (n = 4/age) were sacrificed and sampled at 0 (<12 h of birth), 7, 14, 21, 28, 35, and 42 d of age. From each sample, the basal epithelial layer was traced and expression within the outlined region was quantified using a multispectral imaging system. Fluorescent intensity (FI) of the markers in traced regions on each slide were normalized against a control sample and then evaluated statistically using Mixed procedures in SAS. Samples were also used for subjective assessment of MC marker distribution. Our analysis showed increased staining intensity of CD10 and P63 at d 42, relative to d 0 (P = 0.02). The ratio of CD10 to P63 remained constant (P = 0.94) from d 0 to d 42. The increased intensity with consistent ratio values could be explained by our observation that P63+ nuclei were more closely spaced in younger than older neonates. These results emphasize the importance of assessing expression within individual nuclei rather than simply expression within the entire basal layer, as evaluated by the tracing method used in this study. Double positive (P63+/CD10+) and double negative (P63-/CD10-) cells and single positive cells expressing either marker (P63-/CD10+ and P63+/CD10-) were present in both basal and supra-basal layers. Our data does not allow us to define a sequential progression of MC differentiation in the basal layer. Further studies with additional MC markers are required to define the sequence of bovine MC ontogeny.