Decidualization and expression of insulin-like growth factor-I and insulin-like growth factor binding protein-4 in the periimplantation mouse uterus

In a previous study, insulin-like growth factor-I (ICF-I) and a potential inhibitory binding protein, IGF binding protein-4 (IGFBP-4), were found to be expressed in a cell-specific and temporally dynamic manner in the mouse uterus during the periimplantation period. The mRNA levels of bo th IGF-I and IGFBP-4 rapidly increased between Days 5 and 6 of gestation and then declined after the establishment of embryo implantation. In the current study, we conducted in situ hybridization analysis on pregnant mouse uteri and deciduomata-induced mouse uteri to determine whether the presence of an embryo is required for uterine IGF-I and IGFBP-4 mRNA expression. Our data reveal that before implantation, the maternal hormones of pregnancy support IGF-I and IGFBP-4 mRNA expression. Beyond gestational Day 4, however, decidualization of the uterine stroma, either artificially induced or naturally induced by an implanting embryo, is sufficient for maintaining the expression of these two genes. Thus, the presence of specific embryo factors is not required for ICF-I and IGFBP-4 expression in the periimplantation uterus. These studies indicate that the expression of IGF-I and IGFBP-4 mRNAs may be associated with decidualization of uterine stromal cells. The restricted anatomical and temporal expression of IGF-I and IGFBP-4 mRNAs in the periimplantation uterus suggests a physiologic role for IGF-I and IGFBP-4 in the maintenance and expansion of decidualization.