Abstract
Improved methods are needed to reliably and accurately evaluate oocyte quality prior to fertilization and transfer into the woman of human embryos created through in vitro fertilization (IVF). All oocytes that are retrieved and matured in culture are exposed to sperm with little in the way of evaluating the oocyte quality. Furthermore, embryos created through IVF are currently evaluated for developmental potential by morphology, a criterion lacking in quantitation and accuracy. With the recent successes in oocyte vitrification and storage, clear metrics are needed to determine oocyte quality prior to fertilizing. The first polar body (PB) is extruded from the oocyte before fertilization and can be biopsied without damaging the oocyte. Here, we tested the hypothesis that the PB transcriptome is representative of that of the oocyte. Polar body biopsy was performed on metaphase II (MII) oocytes followed by single-cell transcriptome analysis of the oocyte and its sibling PB. Over 12,700 unique mRNAs and miRNAs from the oocyte samples were compared with the 5,431 mRNAs recovered from the sibling PBs (5,256 shared mRNAs or 97%, including miRNAs). The results show that human PBs reflect the oocyte transcript profile and suggests that mRNA detection and quantification through high-throughput quantitative PCR could result in the first molecular diagnostic for gene expression in MII oocytes. This could allow for both oocyte ranking and embryo preferences in IVF applications.
Highlights
Clinicians need additional metrics for predicting quality of human oocytes for in vitro fertilization (IVF) procedures
We developed a method for quantitative cDNA construction from both a single oocyte and its sibling polar body, and we detected a total of 12,883 genes through mapping of Ͼ27 million reads from these oocytes and polar bodies (Table 1)
This result might be expected because the polar body and oocyte shared a common ooplasm no more than 24 h prior to polar body biopsy, but no less surprising because of the diversity of the transcripts detected in the polar body samples
Summary
Clinicians need additional metrics for predicting quality of human oocytes for IVF procedures. The results show that human PBs reflect the oocyte transcript profile and suggests that mRNA detection and quantification through highthroughput quantitative PCR could result in the first molecular diagnostic for gene expression in MII oocytes This could allow for both oocyte ranking and embryo preferences in IVF applications. The transcriptome of a polar body has never been reported, and a polar body biopsy involves its careful removal through microdissection This procedure can be performed without damaging the sibling oocyte or developing embryo [8] and with advances in oocyte vitrification [9], this could be helpful for patients with ethical objections to fertilizing multiple oocytes and creating supernumerary embryos, or it can be applied to the growing practice of oocyte vitrification for donor egg banking. We are the first to report the analysis of polar body transcriptomes from any organism and analyze its mRNA population with that of its sibling oocyte
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