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
K. Prelle et al., 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, ENDOCRINOL, 142(3), 2001, pp. 1309-1316
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.