Global Gene Expression Profiling of Individual Human Oocytes and Embryos Demonstrates Heterogeneity in Early Development

Abstract

Early development in humans is characterised by low and variable embryonic viability, reflected in low fecundity and high rates of miscarriage, relative to other mammals. Data from assisted reproduction programmes provides additional evidence that this is largely mediated at the level of embryonic competence and is highly heterogeneous among embryos. Understanding the basis of this heterogeneity has important implications in a number of areas including: the regulation of early human development, disorders of pregnancy, assisted reproduction programmes, the long term health of children which may be programmed in early development, and the molecular basis of pluripotency in human stem cell populations. We have therefore investigated global gene expression profiles using polyAPCR amplification and microarray technology applied to individual human oocytes and 4-cell and blastocyst stage embryos. In order to explore the basis of any variability in detail, each developmental stage is replicated in triplicate. Our data show that although transcript profiles are highly stage-specific, within each stage they are relatively variable. We describe expression of a number of gene families and pathways including apoptosis, cell cycle and amino acid metabolism, which are variably expressed and may be reflective of embryonic developmental competence. Overall, our data suggest that heterogeneity in human embryo developmental competence is reflected in global transcript profiles, and that the vast majority of existing human embryo gene expression data based on pooled oocytes and embryos need to be reinterpreted.

Proteomics study reveals that the dysregulation of focal adhesion and ribosome contribute to early pregnancy loss

“…Similar to our results, Shaw et al. also reported the involvement of LAMA5 and LAMB1 in early pregnancy . Upregulation of proteins related to focal adhesion is involved in the increased myometrial contractility, which always occurs at the end of pregnancy .…”

Distinct differences in global gene expression profiles in non-implanted blastocysts and blastocysts resulting in live birth

“…This is in contrast to the study by Yan et al (2013) and other studies (Braude et al, 1988;Dobson et al, 2004;Hamatani et al, 2006;Zhang et al, 2009;Assou et al, 2011a;Kakourou et al, 2012;Shaw et al, 2013) performed on surplus pre-implantation embryos, where the reproductive potential is unknown as the intention is to investigate the genetic programme regulating development, rather than implantation. In order to achieve this goal, we pursued a strategy were we aimed only at identifying genes that were markedly differentially expressed in general between non-implanting embryos and embryos resulting in live birth.…”

“…In comparison, an increasing number of studies have investigated the gene expression of human pre-implantation embryos in order to understand the regulation of early embryonic development (Dobson et al, 2004;Hamatani et al, 2006;Zhang et al, 2009;Wong et al, 2010;Assou et al, 2011b;Kakourou et al, 2013;Shaw et al, 2013). These studies have suggested a number of genes involved in oocyte maturation, maternal-zygotic transition and embryonic-genomic activation.…”

“…The divergence has several likely explanations. Firstly, there is a demonstrated large variation in the expression of individual embryos (Shaw et al, 2013), and as such a high chance of detecting in one blastocyst mRNAs that are not detected in another blastocyst, simply by chance. Furthermore, the analysis in the study by Yan et al (2013) was performed on biopsies from day 6 embryos, whereas the biopsies in our study was obtained on day 5, followed by transfer on day 6.…”

“…The only human study conducted so far identified more than 700 transcripts that were uniquely expressed in human embryos that resulted in pregnancies, thus providing further support to the hypothesis that gene expression may be predictive of pregnancy outcome (Jones et al, 2008). The analysis was performed on pooled samples; a necessary strategy that, however, obscures the heterogeneity of human blastocysts (Shaw et al, 2013). Furthermore, previous studies have predominately used microarrays, the use of which has several limitations such as reliance upon existing knowledge of the genomic sequence, high background levels and a limited dynamic range of detection.…”