Disruption of O‐GlcNAc homeostasis during mammalian oocyte meiotic maturation impacts fertilization

Abstract

Meiotic maturation and fertilization are metabolically demanding processes, and thus the mammalian oocyte is highly susceptible to changes in nutrient availability. O-GlcNAcylation-the addition of a single sugar residue (O-linked β-N-acetylglucosamine) on proteins-is a posttranslational modification that acts as a cellular nutrient sensor and likely modulates the function of oocyte proteins. O-GlcNAcylation is mediated by O-GlcNAc transferase (OGT), which adds O-GlcNAc onto proteins, and O-GlcNAcase (OGA), which removes it. Here we investigated O-GlcNAcylation dynamics in bovine and human oocytes during meiosis and determined the developmental sequelae of its perturbation. OGA, OGT, and multiple O-GlcNAcylated proteins were expressed in bovine cumulus oocyte complexes (COCs), and they were localized throughout the gamete but were also enriched at specific subcellular sites. O-GlcNAcylated proteins were concentrated at the nuclear envelope at prophase I, OGA at the cortex throughout meiosis, and OGT at the meiotic spindles. These expression patterns were evolutionarily conserved in human oocytes. To examine O-GlcNAc function, we disrupted O-GlcNAc cycling during meiotic maturation in bovine COCs using Thiamet-G (TMG), a highly selective OGA inhibitor. Although TMG resulted in a dramatic increase in O-GlcNAcylated substrates in both cumulus cells and the oocyte, there was no effect on cumulus expansion or meiotic progression. However, zygote development was significantly compromised following in vitro fertilization of COCs matured in TMG due to the effects on sperm penetration, sperm head decondensation, and pronuclear formation. Thus, proper O-GlcNAc homeostasis during meiotic maturation is important for fertilization and pronuclear stage development. K E Y W O R D S fertilization, mammalian, meiotic maturation, O-GlcNAc, oocyte

Evidence and manipulation of O-GlcNAcylation in granulosa cells of bovine antral follicles†

“…The current study is the first to detect and characterize O-GlcNAcylation in GCs of bovine antral follicles, but others have reported the existence of OGT and OGA enzymes, and expression of O-GlcNAcylated proteins, in cumulus oocyte complexes (COCs) [ 40 ]. Hyper-O-GlcNAcylation (via Thiamet-G), has no detrimental effects on the cumulus cells or the oocyte, but zygote formation following in vitro fertilization is compromised [ 40 ]. Other investigations report, however, that increased glucose shunting through the HBP (thus potentiating O-GlcNAcylation) has deleterious effects on oocyte health and developmental competence.…”

Protein O-GlcNAcylation Promotes Trophoblast Differentiation at Implantation

“…TMG induced elevation of O-GlcNAcylation levels and kinetics is similar to that caused by cell stresses [ 19 , 34 , 44 , 45 ]. Moreover, TMG has been shown to increase O-GlcNAcylation in oocytes, leading to increased polyspermy [ 46 ], but it has not been used to treat pre-implantation embryos or trophoblast cells. The only previous attempt to elevate O-GlcNAcylation in pre-implantation embryos used the alternative OGA inhibitor PUGNAc [ 26 ], which is known to exhibit off-target effects [ 47 ].…”

NAT10 Maintains OGA mRNA Stability Through ac4C Modification in Regulating Oocyte Maturation

“…O-GlcNAc is recognized as an important regulatory mechanism of cytosolic and nuclear proteins (30). The involvement of O-GlcNAc in regulating mammalian oocyte maturation has been determined in previous literature (31,32). Frank and colleagues have reported that in vitro developmental competence of mouse oocytes was impaired by O-GlcNAc of heat shock protein 90 under hyperglycemic conditions (32).…”