Glycine receptor α4 subunit facilitates the early embryonic development in mice

Abstract

Oviduct fluid is essential for the fertilization and subsequent preimplantation development. Glycine is abundant in oviduct fluid and is reported to be critical for preimplantation development of fertilized eggs in mammals. However, the mechanism by which glycine exerts its action on fertilized eggs is yet to be understood. Here we show that glycine regulates the preimplantation development of mouse fertilized eggs via glycine receptors. Among them, the alpha-4 subunit (Glra4) and the β subunit are expressed in mouse fertilized eggs, and lacking Glra4 inhibits embryonic development to the blastocyst stage, decreases the number of cells in the blastocysts and the litter size. Thus, we identify a novel function of the glycine receptor, which is considered to act mainly as a neurotransmitter receptor, as a regulator of embryonic development and our data provide new insights into the interactions between oviduct milieu and mammalian fertilized egg.

Perspective: One-Cell and Cleavage-Stage Mouse Embryos Thrive in Hyperosmotic Oviductal Fluid Through Expression of a Glycine Neurotransmitter Transporter and a Glycine-Gated Chloride Channel: Clinical and Transgenerational Implications

“…Finally, Glra4-knockout slowed preimplantation development of fertilized mouse eggs, and the resultant blastocysts had fewer cells. Litter sizes were also smaller in Glra4-knockout mice (Nishizono et al, 2020). Thus, glycine-stimulated chloride influx likely fosters mouse one-cell and cleavage-stage development in vivo.…”

“…These receptors are glycine-gated chloride channels. GLRA4 is expressed in fertilized mouse oocytes and early embryos, while GLRA1 is expressed in fertilized bovine oocytes, and GLRA2 is expressed in human zygotes (Nishizono et al, 2020). Finally, Glra4-knockout slowed preimplantation development of fertilized mouse eggs, and the resultant blastocysts had fewer cells.…”

“…When cultured in somewhat hypotonic, glycine-containing medium, fertilized mouse eggs are inhibited in their progression to the four-cell stage and arrest as morula when cultured with the glycine-receptor inhibitors, strychnine and PMBA (Nishizono et al, 2020). These receptors are glycine-gated chloride channels.…”

“…To further complicate work to reproduce in vivo conditions in vitro, one-cell and cleavage-stage embryos from different strains of mice exhibit different thresholds of susceptibility to impaired development by hypertonic media, although glycine rescues development in all of the strains that have been tested (Suzuki et al, 1996;Hadi et al, 2005). Nevertheless, human as well as mouse zygotes express a glycine neurotransmitter transporter and a glycine-gated chloride channel (Baltz and Tartia, 2010;Nishizono et al, 2020), and these transport proteins are likely important to the development of early embryos of both species in vivo. Possibly because early human embryos develop in vitro in non-physiological conditions, children conceived by ART have increased risk of preterm birth, low and high birth weight, birth defects, and metabolic dysfunction (Feuer and Rinaudo, 2012).…”

“…More recently, the glycine-gated chloride channel, GLRA4, was also shown to facilitate development of fertilized mouse eggs into blastocysts (Nishizono et al, 2020). This channel appears to catalyze chloride uptake by embryonal cells in the presence of glycine.…”