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 potent ial 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 leve ls of bo th IGF-I and IGFBP-4 rapidly increased between Days 5 and 6 o f gestation and then declined after the establishment of embryo implan tation. In the current study, we conducted in situ hybridization analy sis on pregnant mouse uteri and deciduomata-induced mouse uteri to det ermine 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 ex pression. Beyond gestational Day 4, however, decidualization of the ut erine stroma, either artificially induced or naturally induced by an i mplanting embryo, is sufficient for maintaining the expression of thes e two genes. Thus, the presence of specific embryo factors is not requ ired 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 r estricted anatomical and temporal expression of IGF-I and IGFBP-4 mRNA s in the periimplantation uterus suggests a physiologic role for IGF-I and IGFBP-4 in the maintenance and expansion of decidualization.