374 SEX-DEPENDENT METABOLIC DIFFERENCES OF BOVINE PREIMPLANTATION EMBRYOS

Abstract

Sex-dependent differences in mammalian embryo phenotype are apparent at the preimplantation stage of development, before the appearance of sex-specific cells. The ratio of male:female embryos may be modified by environmental factors such as maternal diet in vivo and the composition of embryo culture media in vitro. We have used amino acid profiling (AAP), a defined, non-invasive metabolic marker of developmental potential to compare the effect of sex on the metabolism of bovine preimplantation blastocysts and expanded blastocysts conceived in vivo (n = 35) or produced in vitro (n = 172). Blastocysts were incubated individually for 24 h in synthetic oviduct fluid medium plus a close-to-physiological mixture of amino acids. The depletion or appearance of 18 amino acids was measured using high-performance liquid chromatography. Blastocysts were then sexed by PCR and the outcome related to AAP. Amino acid depletion by in vitro-produced blastocysts was higher than in embryos conceived in vivo (P = 0.02). Net appearance of amino acids was higher in the medium from early blastocysts produced in vitro (P = 0.018) although this rise was lost at the expanded stage. There were marked differences in the amino acid profiles of male and female embryos produced in vitro: female embryos exhibited significantly increased depletion of arginine, glutamate, and methionine and appearance of glycine, while male embryos displayed increased depletion of phenylalanine, tyrosine, and valine. Overall, in vitro-produced blastocysts exhibited gender-specific differences in metabolic profiles of 7 out of 18 amino acids; in vivo-produced blastocysts exhibited differences in 2 out of 18 amino acids. These differences had disappeared by the expanded blastocyst stage. Our experiments reveal striking differences in the metabolism of preimplantation embryos conceived in vivo and in vitro, some of which, particularly in the case of the in vitro-produced embryos, are dependent on embryo sex. Moreover, in vivo-derived embryos tend to have a reduced metabolism consistent with the Quiet Embryo Hypothesis, which proposes that higher quality embryos have less molecular and cellular damage than those of a lower quality and thus have a reduced need to take up nutrients for repair processes. Supported by a Wellcome-VIP/University of York Fellowship to RGS.