Regulated temporal and spatial expression of the calcium-binding proteins calcyclin and OPN (osteopontin) in mouse tissues during pregnancy

In situ hybridization and northern/slot blot analyses were used to quantify the expression of calcyclin (2A9, 5B10), osteopontin (opn, secreted phosphoprotein, 2ar) and calmodulin mRNAs in mouse tissues that support pregnancy. High-to-moderate levels of the mRNAs of all three genes were detected at discrete locations in the uterus, decidua and placenta as a function of gestation time. Calmodulin expression was constant in these tissues; calcyclin mRNA was high during early pregnancy and declined after day 8-9 of gestation; and opn mRNA was undetectable before day 7, with maximal levels on days 9-12 in each of these tissues. Calcyclin, but not opn, expression was also observed in the chorioamnion after day 12. Calcyclin was expressed throughout the decidua on day 8 but became restricted to the primary (antimesometrial) decidual zone and decidua lateralis on day 9, and the decidua capsularis after day 9. By contrast, opn mRNA was localized on day 9 to the mesometrial triangle, which contains a large population of granulated metrial gland cells, and to the decidua basalis. These two genes may serve as markers for the two types of decidual tissue. We suggest that one function of OPN, which may be an indicator of cells in the decidua that have a bone marrow genealogy, is to mediate the flux of calcium from the maternal circulation to the developing embryo.