Abstract
BackgroundDynamic changes of histone posttranslational modifications are important contexts of epigenetic reprograming after fertilization in pre-implantation embryos. Recently, lactylation has been reported as a novel epigenetic modification that regulates various cellular processes, but its role during early embryogenesis has not been elucidated.ResultsWe examined nuclear accumulation of H3K23la, H3K18la and pan histone lactylation in mouse oocytes and pre-implantation embryos by immunofluorescence with specific antibodies. All of the three modifications were abundant in GV stage oocytes, and both H3K23la and pan histone lactylation could be detected on the condensed chromosomes of the MII oocytes, while H3K18la were not detected. After fertilization, the nuclear staining of H3K23la, H3K18la and pan histone lactylation was faint in zygotes but homogeneously stained both of the parental pronuclei. The signal remained weak in the early cleavage stage embryos and increased remarkably in the blastocyst stage embryos. Comparison of the embryos cultured in four different conditions with varying concentrations of oxygen found that H3K23la, H3K18la and pan histone lactylation showed similar and comparable staining pattern in embryos cultured in atmospheric oxygen concentration (20% O2), gradient oxygen concentration (5% O2 to 2% O2) and embryos obtained from in vivo, but the modifications were greatly reduced in embryos cultured in hypoxic condition (2% O2). In contrast, nuclear accumulation of H3K18ac or H3K23ac was not significantly affected under hypoxic condition. Moreover, the developmental rate of in vitro cultured embryo was significantly reduced by low oxygen concentration and small molecule inhibition of LDHA activity led to decreased lactate production, as well as reduced histone lactylation and compromised developmental rate.ConclusionsWe provided for the first time the dynamic landscape of H3K23la, H3K18la and pan histone lactylation in oocytes and pre-implantation embryos in mice. Our data suggested that histone lactylation is subjected to oxygen concentration in the culture environment and hypoxic in vitro culture reduces histone lactylation, which in turn compromises developmental potential of pre-implantation embryos in mice.
Highlights
Gamete genomes undergo widespread epigenetic reprogramming to restore totipotency in zygotes [1, 2]
Paternal and maternal pronuclei were all homogeneously stained with pan histone lactylation, Histone H3 lysine23 lactylation (H3K23la) and H3K18la at different pronuclear stages of zygotes, except from the absence of H3K18la from the parental genome just after fertilization around 2 hpi (Additional file 1: Fig. S1A–C). These results demonstrated the nuclear presence of pan histone lactylation, H3K23la and H3K18la in oocytes and pre-implantation embryos and showed that there was no asymmetry for histone lactylation between male and female pronuclei in the zygotes
The developmental rate of blastocysts was reduced by 54% after GSKA treatment (Fig. 6D, E). These results suggested that 100 pmol of GSKA effectively inhibited Lactate dehydrogenase A (LDHA) activity and led to reduced production of lactate, which in turn led to lower histone lactylation and impaired embryonic developmental. (See figure on page.) Fig. 3 Nuclear accumulations of H3K23la and H3K18la in pre-implantation embryos under different oxygen conditions. a–d Long-term hypoxic in vitro culture significantly reduced H3K23la in blastocyst stage embryos
Summary
Gamete genomes undergo widespread epigenetic reprogramming to restore totipotency in zygotes [1, 2]. Histone lactylation promotes expression of macrophage pro-fibrotic genes in lung myofibroblast, and regulates key genes related to cell metabolism in non-small cell lung cancer cells [13, 14]. Gli-like transcription factor 1 (Glis1) activates glycolysis and elevates both histone acetylation and lactylation levels, which coordinately up-regulates expression of pluripotency genes to promote cellular reprogramming [15]. Lactylation has been shown to be involved in infection, cancer, differentiation and biosynthesis, but its role during fertilization and early embryogenesis has not been elucidated [18]. Lactylation has been reported as a novel epigenetic modification that regulates various cellular processes, but its role during early embryogenesis has not been elucidated
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