Embryo biopsy transcriptomics: a potential tool to identify transcripts directly related to the ability of the embryo to induce pregnancy after transfer.

Abstract

The incidence of pregnancy loss due to embryonic mortality in cattle is one of the major causes of reproductive failure. The early embryonic loss can be due to problems with the embryo itself, the uterine environment, or interactions between the embryo and the uterus. So, this study was conducted to investigate the gene expression profile of bovine embryo biopsies produced in vivo and in vitro that resulted in different pregnancy outcomes. For this, biopsies representing 30 to 40% of the intact in vitro and in vivo blastocysts were taken, and 60 to 70% part was allowed to re-expand prior to transfer to recipients. Based on the pregnancy outcome after transfer, biopsies (n = 10 per pool) were grouped into 3 distinct phenotypes: those that resulted in no pregnancy, those that resulted in resorption, and those that resulted in successful pregnancy and subsequent calf delivery. A bovine cDNA microarray with 2000 clones was used to analyze the gene expression profiles of 3 replicates from each embryo biopsy group. Array data analysis revealed a total of 50 and 52 genes to be differentially expressed between biopsies derived from in vivo blastocysts that resulted in no pregnancy v. calf delivery and resorption v. calf delivery, respectively. Similarly, a total of 52 and 58 transcripts were differentially expressed between biopsies derived from in vitro-produced blastocysts that resulted in no pregnancy v. calf delivery and resorption v. calf delivery, respectively. Quantitative real-time PCR has confirmed the expression profile of 6 selected candidate genes. A distinct set of genes were found to be commonly expressed between in vitro- and in vivo-derived blastocyst biopsies, which ended up with the same pregnancy outcome. Biopsies, which ended up with calf delivery, were found to be enriched with transcripts involved in nucleosome assembly (KRT8), translation (RPLPO), electron transport (COX-2), and placenta specific (PLAC8). On the other hand, transcripts regulating immune response (TNFa), response to stress (HSPD1), and cell adhesion (CD9) were up-regulated in embryos that resulted in no pregnancy or resorption. Differences in transcript abundance of some genes have been seen between biopsies derived from in vitro and in vivo blastocysts. Biopsies from in vivo-derived blastocysts and that ended up with resorption were found to be enriched with transcripts regulating calcium-binding protein (S100A10, S100A14). Transcription factor-related transcripts (CDX2, HOXB7) were up-regulated in vitro-derived blastocyst biopsies that resulted in no pregnancy. In conclusion, the results evidenced that embryos derived from either in vitro or in vivo have more similarities than differences in their transcript abundance with respect to the ability in initiating pregnancy.