Insulin-like growth factor I (IGF-I) and long R(3)IGF-I differently affectdevelopment and messenger ribonucleic acid abundance for IGF-binding proteins and type IIGF receptors in in vitro produced bovine embryos

The insulin-like growth factor (IGF) system is a complex network, including ligands (IGF-I and -II), binding proteins (IGFBP-1 to -6), and receptors, of which the type I IGF receptor (IGF-I-R) is important for transmission of most biological effects of IGFs. As IGFs are secreted in large amounts by the female reproductive tract, it has been hypothesized that maternal IGFs may affect embryonic growth and differentiation in a fine-tuned manner, inv olving modulation of IGF effects by embryonic IGFBP and IGF-I-R expression. To address this point, we cultured in vitro produced bovine embryos in a c hemically defined culture system in the presence (100 ng/ml) of recombinant human IGF-I, long R(3)IGF-I (LR3), or without IGF supplementation (control ). The affinity of LR3 to IGFBPs measured by competition assays and Western ligand blots is at least 3 orders of magnitude lower than that of IGF-I. L R3 was most efficient in stimulating early embryonic cleavage, whereas furt her development was most potently supported by IGF-I. Total cell numbers of blastocysts were highest in the presence of LR3 (105 +/- 4), followed by I GF-I (96 +/- 5), and the control group (91 +/- 3; P < 0.05). Differential c ell staining of blastocysts revealed that these differences were mainly rep resented by trophectoderm cell numbers. Analysis of messenger RNA (mRNA) ex pression for IGFBPs and IGF-I-R was performed by RT-real-time PCR, using ex pression of the nonregulated housekeeping gene glyceraldehyde-3-phosphate d ehydrogenase for normalization. Embryonic IGFBP-3 mRNA levels in the LR3 tr eatment group were 1.7-fold (P < 0.001) and 2.8-fold (P < 0.001) higher tha n those in the IGF-I and control groups, respectively. IGFBP-5 mRNA levels were about a-fold (P < 0.001) elevated in both IGF treatment groups, with s lightly (P < 0.05) higher levels in IGF-I- than in LR3-treated embryos. Sim ilarly, IGFBP-3 mRNA abundance was increased (P < 0.05) in embryos from the IGF-I us. the LR3 culture system. IGF-I-R mRNA levels were reduced by IGF- I (80% of control; P < 0.01), but increased by LR3 (1.3-fold us, control; P < 0.001). These data show that the affinity for IGFBPs of IGF peptides is relevant for their effects on preimplantation embryos and affects different parameters, i.e. development, cell numbers, and mRNA expression for compon ents of the IGF system, in different directions.