Effects of Embryo Production Systems on Angiogenesis and Development of Bovine Placentas

Abstract

Placental abnormalities have been reported following the transfer of in vitro-produced (IVP) and cloned (somatic cell nuclear transfer; SCNT) embryos in cattle and sheep. The overall objective of this research was to determine the effects of embryo production systems (IVP and NT) on angiogenesis and development of placentas during early and late gestation in cattle. Angiogenesis was assessed by the expression of vascular endothelial growth factor (VEGF), peroxisome proliferator-activator receptor-gamma (PPARγ), and vascular morphometry. During late gestation (Day 222), angiogenesis and morphometry of placentas were assessed in placentas from embryos produced in vivo and in vitro using undefined, serum-supplemented medium (IVPS). During early gestation (Day 70), the effects of embryo culture media (undefined, IVPS or semi-defined modified synthetic oviductal fluid, mSOF) on angiogenesis and morphometry of placentas were evaluated. Finally, at Day 40 of gestation angiogenesis and development were compared in placentas from embryos produced in vivo, in vitro using G1.2/G2.2 media, or by SCNT.

The results described in this dissertation demonstrated that angiogenesis as well as development of placentas differed depending on embryo production system and day of gestation. During late gestation, placentas from the IVPS group had decreased percentage of placentome surface area which was associated with increased expression of PPARγ protein and increased blood vessels-to-placentome surface area ratios. These findings suggest that during late gestation compensatory mechanisms exist in the vascular beds of placentas from bovine embryos produced in vitro. In contrast, during early gestation (Day 70) placentas from the IVPS group developed similar to in vivo controls; whereas placentas from the mSOF group had decreased densities of fetal and maternal blood vessels associated with a decreased expression of VEGF mRNA in cotyledons. At Day 40 of gestation, placentas from embryos produced using G1.2/G2.2 media appeared to have more compromised vascular development compared with placentas from embryos produced in vivo or by SCNT.