Investigating effects of environmentally acquired epigenetic factors on the mammalian embryo transcriptome
Krykbaeva, Marina
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Abstract
The major aim of this work is to shed light on epigenetic effects on embryonic development. To this end, we implemented two experimental paradigms. First, we investigated the effect of maternal diet on the embryonic transcriptome. We used in vitro fertilization to isolate gamete-carried factors and single-embryo RNA-Seq to produce a high-resolution data set in 4-cell, morula, and blastocyst embryos, as well as oocytes. We found that although differential expression was observed in most stages of development, these changes were fairly small in size. Likewise, offspring created using an embryo transfer procedure did not exhibit phenotypic differences as a result of maternal diet. However, alterations in gene expression of mitochondrial respiration and lipid and cholesterol metabolism genes were detected in offspring tissue with a clear sex bias. Second, we compared transcriptomes of embryos produced using three methods of fertilization – natural mating (NM), in vitro fertilization (IVF), and intracytoplasmic sperm injection (ICSI) as well as parthenogenesis. The largest differences were detected in IVF embryos, largely in the categories of translation and ribosome biogenesis. ICSI embryos exhibited a small deviation in differentiation-associated gene expression. Parthenogenesis, an embryo-like system with no paternal contributions, resulted in vast expression changes encompassing ~20% of expressed genes and was further used as a model system to confirm a role for sperm-carried RNAs in regulating embryo gene expression. Lastly, this single-embryo data set was used to characterize stochasticity in gene expression and confirm the presence of both “quiet” and “noisy” genes. Overall, we provide two large-scale data sets comprised of hundreds of embryos, which serves as a systematic approach to investigating the effect of epigenetic factors on the embryonic transcriptome.