Qa. Winger et al., BOVINE OVIDUCTAL AND EMBRYONIC INSULIN-LIKE-GROWTH-FACTOR BINDING-PROTEINS - POSSIBLE REGULATORS OF EMBRYOTROPHIC INSULIN-LIKE-GROWTH-FACTOR CIRCUITS, Biology of reproduction, 56(6), 1997, pp. 1415-1423
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.