Abstract
BackgroundSince the development of in vitro embryo production in cattle, different supplements have been added to culture media to support embryo development, with serum being the most popular. However, the addition of serum during embryo culture can induce high birthweights and low viability in calves (Large Offspring Syndrome). Analysis of global gene expression in bovine embryos produced under different conditions can provide valuable information to optimize culture media for in vitro embryo production.ResultsWe used RNA sequencing to examine the effect of in vitro embryo production, in either serum-containing or serum-free media, on the global gene expression pattern of individual bovine blastocysts. Compared to in vivo derived embryos, embryos produced in serum-containing medium had five times more differentially expressed genes than embryos produced in serum-free conditions (1109 vs. 207). Importantly, in vitro production in the presence of serum appeared to have a different impact on the embryos according to their sex, with male embryos having three times more genes differentially expressed than their female counterparts (1283 vs. 456). On the contrary, male and female embryos produced in serum-free conditions showed the same number (191 vs. 192) of genes expressed differentially; however, only 44 of those genes were common in both comparisons. The pathways affected by in vitro production differed depending on the type of supplementation. For example, embryos produced in serum-containing conditions had a lower expression of genes related to metabolism while embryos produced in serum-free conditions showed aberrations in genes involved in lipid metabolism.ConclusionsSerum supplementation had a major impact on the gene expression pattern of embryos, with male embryos being the most affected. The transcriptome of embryos produced in serum-free conditions showed a greater resemblance to that of in vivo derived embryos, although genes involved in lipid metabolism were altered. Male embryos appeared to be most affected by suboptimal in vitro culture, i.e. in the presence of serum.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2393-z) contains supplementary material, which is available to authorized users.
Highlights
Since the development of in vitro embryo production in cattle, different supplements have been added to culture media to support embryo development, with serum being the most popular
All the uniquely mapped fragments corresponded to annotated genes and of, an average of 62, 67, and 71 % mapped to annotated exons; the remainder overlapped with annotated introns (Tables 1 and Additional file 1: Table S1, Fig. 1d)
Embryos produced under serum-free conditions showed gene expression patterns that were more similar to those derived in vivo than embryos produced in vitro in the presence of serum
Summary
Since the development of in vitro embryo production in cattle, different supplements have been added to culture media to support embryo development, with serum being the most popular. Cattle embryos produced in serum-free conditions scored higher when using traditional parameters to evaluate embryo quality [5, 6] These quality parameters are based on blastocyst development, blastocyst cell number, ratios of inner cell mass (ICM) and trophectoderm cells, apoptotic cell ratios [6], and the gene expression pattern of a limited number of selected genes analyzed by qPCR [7, 8]. The selection of only a few genes to check embryo quality was based on the fact that the evaluation of expression of all the genes in the genome by qPCR was a daunting task This no longer represents an obstacle with recently developed RNA sequencing techniques, which have proven to be a very powerful tool for evaluating and comparing the global gene expression pattern of even single cells, and of single embryos [3, 9]. This new technique allows the study of associated pathways that may be involved in affecting embryo quality
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