Large-scale transcriptional analysis of bovine embryo biopsies in relation to pregnancy success after transfer to recipients

Abstract

The purpose of this work is to address the relationship between transcriptional profile of embryos and the pregnancy success based on gene expression analysis of blastocyst biopsies taken prior to transfer to recipients. Biopsies (30-40% of the intact embryo) were taken from in vitro-produced day 7 blastocysts (n = 118), and 60-70% were transferred to recipients after reexpansion. Based on the success of pregnancy, biopsies were pooled in three groups (each 10 biopsies) namely: those resulting in no pregnancy (G1), resorbed embryos (G2), and those resulting in calf delivery (G3). Gene expression analysis of these groups was performed using home-made bovine preimplantation-specific cDNA array (219 clones) and BlueChip (with approximately 2,000 clones). Microarray data analysis results revealed a total of 52 and 58 genes were differentially regulated during comparison between G1 vs. G3 and G2 vs. G3. Biopsies resulted in calf delivery were enriched with genes necessary for implantation (COX2 and CDX2), carbohydrate metabolism (ALOX15), growth factor (BMP15), signal transduction (PLAU), and placenta-specific 8 (PLAC8). Biopsies from embryos resulting in resorption are enriched with transcripts involved protein phosphorylation (KRT8), plasma membrane (OCLN), and glucose metabolism (PGK1 and AKR1B1). Biopsies from embryos resulting in no pregnancy are enriched with transcripts involved inflammatory cytokines (TNF), protein amino acid binding (EEF1A1), transcription factors (MSX1, PTTG1), glucose metabolism (PGK1, AKR1B1), and CD9, which is an inhibitor of implantation. In conclusion, we generated direct candidates of blastocyst-specific genes which may play an important role in determining the fate of the embryo after transfer.

Biological differences between in vitro produced bovine embryos and parthenotes

“…The PLAC8, an invasion specific gene, is more abundant in blastocysts resulting in calf delivery compared with those resulting in resorption (El-Sayed et al 2006), and in endometrium of pregnant as compared with non-pregnant cows (Galaviz-Hernandez et al 2003, Klein et al 2006. These findings suggest a potential role for PLAC8 in placental development and fetus-maternal interface.…”

“…Inhibition of PTGS2 increases pregnancy rates after embryo transfer and lowers PGF2a release (Scenna et al 2005). Expression of PTGS2 is more abundant in blastocysts resulting in calf delivery compared with those resulting in resorption (El-Sayed et al 2006). In bovine, the PTGS2 protein localizes to the TE, while the ICM does not express PTGS2 (Charpigny et al 1997), suggesting that this gene is necessary for the elongation and subsequent implantation.…”

“…AKR1B1 is also known as the cause for cell apoptosis in somatic cells that accumulate sorbitol (Galvez et al 2003, Wirtu et al 2004. Expression of AKR1B1 has been detected in endometrium (Madore et al 2003) and also in IVF bovine embryos (Dode et al 2006, El-Sayed et al 2006 and is associated with failure to establish pregnancy and resorption (El-Sayed et al 2006). Perhaps, AKR1B1 contributes to deciding the fate of the embryo through activation of apoptotic mechanisms.…”

“…The ubiquitous protein disulfide reductase TXN plays a role in the mouse implantation (Nonogaki et al 1991), and responds to oxidative stress in bovine and mouse embryos (Nonogaki et al 1991, Bing et al 2003. The TXN gene is downregulated in embryos that fail to give pregnancies and those leading to resorption (El-Sayed et al 2006), while the addition of the compound to a pig embryo culture improves blastocyst formation, cell numbers, and apoptosis (Ozawa et al 2006). The upregulation of TXN in parthenotes could be beneficial to the short-term survival of these blastocysts.…”

Preimplantation embryo programming: transcription, epigenetics, and culture environment

“…Few studies have attempted to correlate the differences in mRNA abundance observed at the blastocyst stage, such as those outlined above, with the ability of the embryo to establish a pregnancy. One such study (El-Sayed et al 2006) addressed the relationship between transcriptional profile of embryos and the pregnancy success based on gene expression analysis of blastocyst biopsies taken prior to transfer to recipients. Microarray data analysis revealed a total of 52 differentially regulated genes between embryos resulting in a calf delivery versus those not resulting in a pregnancy.…”