102 EVIDENCE FOR PRE-IMPLANTATION ORIGIN OF PLACENTAL FAILURE IN BOVINE CLONE PREGNANCIES

Abstract

Placental abnormalities account for a high proportion of pregnancy loss after transfer of cloned (SCNT) bovine embryos. The high rate of pregnancy failure has been linked to the finding of abnormal placental formation and function. Because bovine SCNT embryos were shown to exhibit altered trophoblast differentiation (Arnold DR et al. 2006 Reproduction 132, 279–290), we hypothesized that placental abnormalities in bovine clone pregnancies may originate from disturbed embryo-maternal communication in the pre-implantation period. To test this hypothesis, we evaluated the response of the endometrium to SCNT v. IVF embryos. The SCNT embryos were produced from fibroblast cultures derived from 4 different fetuses to exclude specific effects of a particular donor cell culture. After SCNT or IVF, embryos were cultured under identical conditions. Two SCNT or IVF blastocysts (grade 1) were transferred per recipient heifer (Day 8 of estrous cycle). Ten days later the recipients were slaughtered, the uteri were recovered, and pregnancy was verified by the presence of at least one normally developed embryo. Endometrium samples of 9 SCNT and 10 IVF pregnancies were used for transcriptome profiling with a custom cDNA microarray (BOE array; Bauersachs S et al. 2007 J. Dairy Sci. 90, 4420–4423). In total, 58 transcripts were found to be differently abundant between endometrium samples from SCNT v. IVF pregnancies (SAM, FDR 5.24%). Interestingly, for some of them an important role in implantation and/or placentation has already been shown. NR2F2, encoding the orphan nuclear receptor superfamily member NR2F2 (COUP-TFII), was downregulated in endometrium from SCNT pregnancies (1.5-fold; P < 0.01). Uterine-specific Nr2f2 mutant mice are infertile due to implantation failure (Kurihara I et al. 2007 PLoS Genetics 3, e102). Another interesting candidate is GJA1, encoding connexin 43 (Cx43), with 1.8-fold (P < 0.001) downregulated transcript levels in SCNT pregnancies. A striking increase of stromal Cx43 has been observed in the ovine intercaruncular and caruncular endometrium during intensification of the feto-maternal contact (Gabriel et al. 2005 Placenta 25, 287–296), suggesting that reduced GJA1 mRNA expression in bovine clone pregnancies may negatively affect placentation. In view of the well-orchestrated spectrum of transcriptome changes in endometrium during the peri-attachment period (Bauersachs S et al. 2006 Reproduction 132, 319–331), these findings suggest that placental failure in bovine clone pregnancies may originate from abnormal embryo-maternal communication already in the pre- or peri-implantation period. This study was supported by the Deutsche Forschungsgemeinschaft (FOR 478).