ER-positive cells also develop in endometrial epithelium of mice and rats postnatally. Immunohistochemical detection of ER in CD-1:CRL and CD-1[1CR]BR mice revealed that stromal cells were strongly ER positive on Day 1 (birth), while uterine epithelium was only weakly positive by PND 4. However, different strains of mice exhibit different developmental expression patterns for ER. For example, BALB/c mice have ER-negative uterine epithelium until PND 6 (where Day 0 = birth), while C57BL/TW mice have ER-positive stroma at birth and develop ER-positive epithelium by PND 5. Thus, within a species, there can be distinct patterns of uterine ER acquisition. In general, however, the murine endometrium becomes ER positive after birth in a cell-specific manner. In rats, uterine glands appear first on PND 9 and increase dramatically in number between PND 10 and 15. Using ISH, Fishman et al. showed that rat uterine stroma contains ER mRNA on the day of birth. However, ER mRNA was not detected in LE until PND 7, or in GE until PND 11. Thus, in both the mouse and rat, endometrial stromal cells are first to produce ER, followed by LE and, finally, GE. The latter event occurs coincidentally with the appearance of uterine glands. buy asthma inhalers
Patterns of endometrial ER expression in the neonatal pig are spatially unique in comparison to that in rodents. As reviewed above, ER-positive character in porcine endometrial epithelium develops first in GE cells. Although a few ER-positive LE cells can be found, this epithelial compartment is still effectively ER negative on PND 15, when GE cells are intensely ER positive. This pattern is almost perfectly complementary to that observed for DNA synthesis in GE and LE cells as determined by autoradiography of [methyl-3H]thymidine-labeled porcine uterine tissues obtained at birth and on PND 14.