Expression of insulin-like growth factor-I (IGF-I) and its receptor in the peri-implantation mouse uterus, and cell-specific regulation of IGF-I gene expression by estradiol and progesterone

This study describes the expression of insulin-like growth factor-I (IGF-l) and IGF-I receptor (IGF-lR) genes in the mouse uterus during the pen-implantation period (Days 1-6 of pregnancy), as well as effects of estradiol (F) and progesterone (P) on cell-specific IGF-l gene expression in the uterus of the ovariectomized adult mouse, Northern blot analysis showed that IGF-I mRNA levels were low but readily detectable in the uterus on Day 1 of pregnancy and steadily increased, reaching high levels just before (Day 4) and after initiation of implantation (Days 5 and 6). In general, IGF-[R transcripts were present in low abun-dance in uterine RNA throughout the pen-implantation period. However, six sizes of uterine IGF-IR transcripts were detected, and the relative abundance of two of these transcripts varied significantly during the peri-implantation period. Cell-specific expres-sion of the IGF-l gene was examined by in situ hybridization to mRNA and immunohistochemical detection of protein. The results indicated that the synthesis of IGF-I on Days 1 and 2 was most predominant in glandular and luminal epithelial cells. However, on Days 3 and 4, stromal cells, and on Days 5 and 6, decidual cells appeared to be the predominant sites of synthesis of this growth factor. Uterine IGF-l gene expression was stimulated by ovarian steroids. Northern blot analysis showed that IGF-I tran-scripts were rare in the ovariectomized adult mouse uterus, but an injection of P and/or F caused a rapid accumulation of these transcripts. Analysis of the cell-specific expression of uterine IGF-I showed that E induced IGF-l gene expression primarily in epithelial cells, whereas P did so in the stroma. Superimposition of E on the P-primed uterus further stimulated IGF-I expressio