206. Effect of in vitro embryo culture on placental gene expression in the sheep

Abstract

In vitro culture (IVC) systems feature commonly in reproductive technologies used in livestock. However, these culture conditions impact on the metabolism and physiology of the developing embryos, as well as on fetal outcome. Culturing rodent embryos in simple defined media results in decreased postimplantation viability and fetal growth rate.1,2 Cytokines and growth factors are present in vivo but are absent from culture and may be causal in the perturbed fetal growth observed. Furthermore, the occurrence of large offspring syndrome (LOS) following embryo IVC in ruminants has been reported and is associated with loss of genetic imprinting.3,4 Abnormal placental development following IVC is also likely to involve perturbed expression of imprinted genes including insulin-like growth factor II (IGF2) and its receptor (IGF2R). The IVC system used for this study included a control embryo transfer group without culture (ET, n = 11), in vitro cultured embryos in serum free defined medium (IVC-NS, n = 10) and in vitro cultured embryos in defined medium with human serum (IVCHS, n = 8). The cultured embryos were transferred to recipient ewes and placentomes were collected at 144–145 days gestation. Fetal weight (kg) was increased in IVCHS (5.15 ± 0.28) compared to ET (4.12 ± 0.24, P = 0.017) and IVC-NS (4.36 ± 0.27). Real-time RT-PCR was used to quantify IGF2 and IGF2R mRNA expression normalized to housekeeper RpP0. Although IGF2 expression was increased in the IVCHS group (2.27 ± 0.44) when compared to ET (1.22 ± 0.37) and IVC-NS (1.17 ± 0.43) groups, this was not significant. In addition, IGF2R expression was increased in the IVCHS (0.008 ± 0.003) group compared to ET (0.003 ± 0.001) and IVC-NS (0.004 ± 0.001) groups, but this was also not significant. IGF2 and IGF2R expression were, however, positively correlated in IVCNS (r = 0.72) and IVCHS (r = 0.95) placentomes, but not control ET placentomes. The presence of serum in IVC promoted fetal growth and increased expression of IGF2 and IGF2R mRNA in placental tissue. Comparison of placental gene expression from IVCHS and naturally mated pregnancies would be valuable to assess the role of serum in placental and fetal development. (1)Bowman & McLaren, 1970.(2)Kaye & Gardner, 1999.(3)Thompson et al., 1995.(4)Young et al., 1998.