BOVINE OVIDUCTAL AND EMBRYONIC INSULIN-LIKE-GROWTH-FACTOR BINDING-PROTEINS - POSSIBLE REGULATORS OF EMBRYOTROPHIC INSULIN-LIKE-GROWTH-FACTOR CIRCUITS

Bovine oviductal monolayer and vesicle primary cultures express insuli n-like growth factor (IGF)-I and -II mRNAs and polypeptides. Early bov ine embryos also express IGF-I, IGF-II, ICF-I receptor, IGF-II recepto r, and insulin receptor mRNAs. This study reports the expression of IG F binding protein (IGFBP) mRNAs and polypeptides in bovine oviduct pri mary cultures and IGFBP mRNAs in preattachment embryos. Release of imm unoreactive IGF-I and ICF-II by oviduct cultures and bovine blastocyst s was also determined. IGFBP-2, -3, -4, and -5 transcripts were observ ed in oviduct primary cultures throughout an 8-day interval. IGFBP-1 a nd -6 mRNAs were consistently not detected in the oviduct. Messenger R NAs encoding IGFBPs -2, -3, and -4 were detected throughout bovine pre attachment development, while transcripts encoding IGFBP-5 were detect ed only in blastocysts. IGFBP-1 and -6 transcripts were not detected i n early embryos. Ligand blot analysis with I-125-labeled ICF-II reveal ed the presence of four prominent polypeptide bands of approximate mol ecular masses 24, 31, and 36 kDa, and a broad band extending from 46 t o 53 kDa, in conditioned media samples prepared from oviduct primary c ultures. Western immunoblot analysis confirmed the identity of the 24- kDa, 31-kDa, and 36-kDa species as IGFBP-4, -5, and -2, respectively. levels of the release of IGF-II from oviductal vesicle cultures were s ignificantly greater than levels observed for monolayer cultures (p < 0.005). No significant difference in the levels of IGF-I release betwe en monolayer and vesicle cultures was observed. Pools of 10 blastocyst s released on average 36.2 +/- 3.9 pg of IGF-II per embryo, while the release of embryonic IGF-I was below the levels of detection for our a ssay. The results suggest that maternally derived IGF may be regulated by IGFBPs to support bovine preattachment development.