Identification and quantification of differentially represented transcripts in in vitro and in vivo derived preimplantation bovine embryos.

Identification of transcripts at key development stages of preimplantation embryos is critical for a better understanding of early embryogenesis. The current study had two aims. The first was to characterize the relative abundance of multiple transcripts during several developmental stages, namely, metaphase II-stage oocytes (MPII), as well as 2-cell, precompact morula (PCM) and in vitro-produced blastocyst (IVTBL) stage embryos. The second was to characterize differences in the relative abundance of transcripts present in in vivo- (IVVBL), in vitro- (IVTBL), and nuclear transfer-derived (NTBL) blastocysts. It was hypothesized that the identification of differentially represented transcripts from these embryos would reveal not only developmentally important genes, but also genes that might be aberrantly expressed due to embryo production techniques. Individual clusters from a large bovine expressed sequence tag (EST) library (http://genome.rnet.missouri.edu/bovine/) of female reproductive tissues and embryos were compared using Fisher's Exact Test weighted by number of transcripts per tissue by gene. Of the 3,144 transcripts that were present during embryogenesis, 125 were found to be differentially represented (P < or = 0.01) in at least one pairwise comparison. Fifteen of these transcripts were selected for further examination using quantitative real-time PCR (qRTPCR) to determine differences in transcript abundance. Twelve of the 15 transcripts were differentially represented (n = 9, P < or = 0.01; n = 3, P < or = 0.05) in at least one pairwise comparison. In summary, identification of differentially represented transcripts in early embryo development, which are modulated by in vitro techniques, should provide markers to ensure the production of embryos closer to those developed in vivo.