Spatio-temporal pattern for expression of galectin-3 in the murine utero-placental complex: evidence for differential regulation

In mice, immunoreactive galectin-3 protein has previously been localized in uterine epithelial cells adjacent to implanting blastocysts as well as in the decidualized endometrium of implantation sites, uterine natural killer cells, and several types of placental trophoblast cells. Because galectin-3 is a soluble extracellular molecule, protein localization by immunohistochemical methods does not demonstrate its cellular origin. Therefore, the present study was undertaken to determine precisely which cell types in the utero-placental complex express galectin-3 mRNA. In situ hybridization results demonstrated that galectin-3 mRNA was expressed throughout the utero-placental complex in all cell types previously shown to contain immunoreactive protein, including uterine epithelium, decidualized endometrium, uterine natural killer cells, and placental trophoblasts. These results indicate that galectin-3 protein is not synthesized in a restricted cell type and translocated through the extracellular spaces to other tissue compartments. Furthermore, Northern blot analysis of total RNA prepared from separated fetal and maternal components of utero-placental complexes demonstrated different patterns of expression for galectin-3 mRNA in the uterus and placenta. Relative levels of galectin-3 mRNA peak at midgestation in the implantation site and during the second half of gestation remain elevated in the placenta but decline in the uterus. Separate mechanisms for regulating expression of galectin-3 on opposite sides of the feto-maternal interface are indicated.