Endometrial expression of mRNA encoding insulin-like growth factors I and II and IGF-binding proteins 1 and 2 in early pregnant ewes.

The temporal variations in endometrial expression of mRNA encoding insulin-like growth factor I (IGF-I) and IGF-II, and insulin-like growth factor-binding protein 1 (IGFBP-1) and IGFBP-2 were investigated between oestrus and day 20 of pregnancy in ewes. Northern blot analysis of endometrial total RNA revealed major transcripts for IGF-I (7.1 kb), IGF-II (5.8 kb), IGFBP-1 (1.3 kb) and IGFBP-2 (1.7 kb). Some minor transcripts for IGF-II were also detected. The low endometrial expression of mRNA encoding IGF-I at day 15 of pregnancy was used as the reference point for time comparison for expression of mRNA encoding IGF-I, IGF-II and IGFBP-2. The mRNA encoding IGFBP-1 was not quantitated since the gene was expressed only on day 15 of pregnancy. Endometrial expression of mRNA encoding IGF-I was increased (P < 0.05) at oestrus and on day 8 of pregnancy relative to expression on day 15, whereas expression of mRNA encoding IGFBP-2 was decreased (P < 0.05). The major IGF-II transcript was unaffected by day of pregnancy. The temporal variation of the expression of mRNAs encoding IGF-I and IGFBP-2 suggests a role for these factors in the uterine environment during early pregnancy in ewes coinciding with rapid development of the embryo and growth of the uterus in preparation for implantation.