STUDY QUESTION: What is the relative effect of common environmental and biological factors on transcriptome changes during
human preimplantation development?
SUMMARY ANSWER: Developmental stage and maternal age had a larger effect on the global
gene expression profile of human preimplantation embryos than the culture medium or oxygen concentration used in in vitro
WHAT IS KNOWN ALREADY: Studies on mouse and bovine embryos have shown that different conditions in the in vitro
culture of embryos can lead to changes in transcriptome profiles. For humans, an effect of developmental stage on the transcriptome
profile of embryos has been demonstrated, but studies on the effect of maternal age or culture conditions are lacking.
DESIGN, SIZE, DURATION: Donated, good quality, day 4 cryopreserved human preimplantation embryos (N = 89) were randomized
to be cultured in one of two culture media (G5 medium or HTF medium) and one of two oxygen concentrations (5% or 20%), with
stratification for maternal age. Next to these variables, developmental stage after culture was taken into account in the
analysis. PARTICIPANTS/MATERIALS, SETTING, METHODS: Embryos that developed to morula or blastocyst stage during these 2 days
whose amplified mRNA passed our quality control criteria for microarray hybridization were individually examined for genome-wide
gene expression (N = 37).
MAIN RESULTS AND THE ROLE OF CHANCE: Based on the number of differentially expressed genes
(DEGs), developmental stage (3519 DEGs) and maternal age (1258 DEGs) had a larger effect on the global gene expression profile
of human preimplantation embryos than either tested culture medium (596 DEGs) or oxygen concentration (492 DEGs) used during
in vitro culture. Interactions between the factors were found, indicating that culture conditions might have a different effect
depending on the developmental stage or the maternal age of the embryos. Affected pathways included metabolism, cell cycle
processes and oxidative phosphorylation.
LIMITATIONS, REASONS FOR CAUTION: Culture of embryos for only 2 days might have
limited the effect on global gene expression by the investigated culture conditions. Earlier stages of development (Day 0
until Day 4) were not analyzed and these embryos might respond differently to the experimental conditions. The freezing and
thawing procedures might have had an effect on gene expression. RT-PCR validation was not performed due to scarcity of the
WIDER IMPLICATIONS OF THE FINDINGS: Our results show that when studying gene expression in single human preimplantation
embryos under various experimental conditions, one should take into account the confounding effect of biological variables,
such as developmental stage and maternal age. This makes these experiments different from gene expression experiments where
these variables can be tightly controlled, for example when using cell lines.
STUDY FUNDING/COMPETING INTERESTS: This
study received no external funding and there were no competing interests.