Flexibility and constraint in preimplantation gene regulation in mouse

Abstract

Although many features of embryonic development exhibit remarkable stability in the face of environmental perturbations, it is also clear that some aspects of early embryogenesis can be modulated by non-genetic influences during and after fertilization. Among potential perturbations experienced during reproduction, understanding the consequences of differing ex vivo fertilization methods at a molecular level is imperative for comprehending both the basic biology of early development and the potential consequences of assisted reproduction. Here, we set out to explore stable and flexible aspects of preimplantation gene expression using single-embryo RNAsequencing of mouse embryos fertilized by natural mating, in vitro fertilization, or intracytoplasmic sperm injection, as well as oocytes parthenogenetically activated to develop (parthenotes). This dataset comprises a resource of over eight hundred individual embryos, which we use for three primary analyses. First, we characterize the effects of each fertilization method on early embryonic gene regulation, most notably finding decreased expression of trophectoderm markers at later stages of preimplantation development in ICSI embryos. Second, we find massive gene misregulation in parthenotes beyond the expected defects in imprinted gene expression, and show that many of these changes can be suppressed by sperm total RNA. Finally, we make use of the single-embryo resolution of our dataset to identify both stablyexpressed genes and highly-variable genes in the early mouse embryo. Together, our data provide a detailed survey of the molecular consequences of different fertilization methods, establish parthenotes as a "tabula rasa" for understanding the role for sperm RNAs in preimplantation gene regulation, and identify subtypes of preimplantation embryos based on their expression of epivariable gene modules.

Epididymal acquired sperm microRNAs modify post-fertilization embryonic gene expression

“…Aside from the role of sperm small RNAs under conditions of stress, the ‘physiologically normal’ pool of sperm small RNA delivered to the egg is involved in regulating early embryonic gene expression and development. The latter has been crudely demonstrated in mice using an approach in which sperm total RNA was introduced to a parthenogenetically activated egg (Conine et al, 2020). Diploid parthenotes develop efficiently to blastocysts and display broad transcriptomic changes throughout preimplantation embryonic development compared to sperm-fertilized embryos (Conine et al, 2020; Park et al, 2013).…”

“…The latter has been crudely demonstrated in mice using an approach in which sperm total RNA was introduced to a parthenogenetically activated egg (Conine et al, 2020). Diploid parthenotes develop efficiently to blastocysts and display broad transcriptomic changes throughout preimplantation embryonic development compared to sperm-fertilized embryos (Conine et al, 2020; Park et al, 2013). Fascinatingly, the introduction of sperm RNA to parthenotes results in changes in expression of hundreds of genes to more closely resemble the expression of a sperm fertilized embryo (Conine et al, 2020).…”

“…Diploid parthenotes develop efficiently to blastocysts and display broad transcriptomic changes throughout preimplantation embryonic development compared to sperm-fertilized embryos (Conine et al, 2020; Park et al, 2013). Fascinatingly, the introduction of sperm RNA to parthenotes results in changes in expression of hundreds of genes to more closely resemble the expression of a sperm fertilized embryo (Conine et al, 2020). In narrowing the role of individual small RNA classes in regulating post-fertilization gene expression, several additional studies have specifically identified post-fertilization functions for sperm microRNAs (miRNAs) in the early embryo (Wang et al, 2022; Yuan et al, 2016).…”