Identifying Molecular Signatures of Genomic Imprinting Errors

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Abstract Alarmingly, ~50 million couples worldwide are unable to conceive after 5 years of unprotected sex. Medically assisted reproductive technologies (ARTs) constitute important treatment modalities for infertile couples trying to conceive. While generally considered safe, ARTs are associated with higher incidences of preterm birth, intrauterine growth restriction, and low birth weight. Moreover, there are more Beckwith-Wiedemann, Silver- Russell, Angelman and Prader-Willi Syndrome children in the ART population harboring imprinted methylation errors compared to those in the general population. Since ART usage coincides with important stages of imprinted DNA methylation programming during gamete and preimplantation development, it is possible that ARTs lead to imprinting errors. Studies in fertile mice support this. Superovulation during oogenesis and/or embryo culture during preimplantation, two nearly universal ART procedures, lead to significant numbers of embryos with imprinted methylation errors. To date, little is known about the regulation of imprinted methylation maintenance during preimplantation development, and moreover, how ARTs lead to disruption in this maintenance. This proposal will address these knowledge gaps. In Aim 1, we will test the hypothesize that embryos are predisposed to imprinted methylation errors because ARTs disrupt crucial maternal-effect transcripts in oocytes that are required in embryos to maintain imprinted methylation. Candidate maternal- effect transcripts will be identified using single cell RNA-seq on control and superovulated oocyte, 1-cell and 2- cell embryos, representing the period of oocyte-to-embryo transition. Candidate function will then be determined though protein degradation methods. Next, we will determine whether altered maternal-effect transcripts in polar bodies, as a proxy for oocytes, correlates with imprinted methylation errors in resulting embryos, ultimately leading to identification of transcript biomarkers that are predictive of imprinted methylation errors. Aim 2 will test the importance of nuclear import in imprint maintenance using pharmacological and protein degradation methods, and whether it is disrupted by ARTs. In Aim 3, we hypothesize that the 4 to 8-cell stages represent a window of susceptibility when fast developing ART embryos acquire DNA methylation errors, particularly in outer, trophoblast cells. We will determine when embryo development is altered by ARTs using time-lapse analysis, and then compare DNA methylation perturbation in slow and fast developing embryos using whole genome bisulfite mutagenesis. This will distill a molecular signature of DNA methylation errors. Next, we will investigate this molecular signature during early development to determine when DNA methylation errors arise and in which lineages of ART embryos, as well as in cells induced to trophoblast fate. Finally, we will test the predictive power of developmental and morphokinetic parameters as a noninvasive procedure for embryos with a molecular signature of imprinted methylation errors. Results from this proposal will provide the biological basis for improvements to fertility treatments aimed at identifying at-risk embryos.