Embryonic MTHFR contributes to blastocyst development

SHMT2 is essential for mammalian preimplantation embryonic development through de novo biosynthesis of nucleotide metabolites

Assisted reproductive technology (ART) is used widely and efficiently to treat infertility. During the ART procedure, one of the main factors affecting the success rate is abnormal development of preimplantation embryos. The establishment and maintenance of developmental competence are precisely regulated at different levels, while minor errors at early stages may result in adverse outcomes, including developmental arrest and implantation failure. As one of the major inputs, the regulatory mechanisms of metabolites in embryonic development are less known. In this study, we investigated the functional relevance of the metabolic enzyme serine hydroxymethyltransferase 2 (SHMT2) and deoxyribonucleotide (dNTP) metabolites in mouse preimplantation embryonic development. By using a well-characterized SHMT2 inhibitor, SHMT-IN-2, we effectively inhibited the catalytic activity of the SHMT2 enzyme, which led to developmental arrest at the pronuclear stage of the embryo. A low-input liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and applied for detecting dNTP content in embryos. We found that SHMT2 inhibition led to an insufficient dTTP supply and replication stress during the first mitotic cleavage, thereby causing failure of pronuclear fusion and developmental arrest. Our findings demonstrate a specific mechanism where, apart from building blocks of DNA, the availability of dNTPs contributes to the control of mouse preimplantation embryonic development.

Associations between maternal MTHFR polymorphisms and embryological outcomes in Korean patients with infertility undergoing IVF/ICSI cycles

OBJECTIVE

Methylenetetrahydrofolatereductase (MTHFR) is important for folate metabolism, which is involved in DNA synthesis and cell growth. However, the relationship between Maternal MTHFR polymorphisms and outcomes in assisted reproduction remains controversial. This is the first study to explore the effect of MTHFR polymorphisms on the embryological outcomes in in vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI) cycles in Korean patients with infertility.

MATERIALS AND METHODS

This retrospective cohort study included 173 women who underwent MTHFR genotyping between July, 2021 and June, 2022. The embryologic outcomes of 301 IVF/ICSI cycles were compared between groups according to MTHFR polymorphisms using ANOVA and Chi-square test.

RESULTS

Oocyte maturation rates were 80.0%, 75.0%, and 71.4% for MTHFR 677CC, 677CT, and 677TT, respectively. Cleaved embryo formation and transplantable embryo rates were comparable across various maternal MTHFR 677 genotypes. Good-quality embryo (GQE) rate was higher for MTHFR 677CT than those for 677CC and 677TT (40.0% vs. 29.4%, p = 0.001 and 40.0% vs. 33.3%, p = 0.025, respectively). When analyzing the combined MTHFR genotypes, the oocyte maturation rate was significantly lower in 677TT than in 677CC 1298AA/677CC 1298AC and 677CC 1298CC/677CT 1298AA/677CT 1298AC (71.4% vs. 76.7%, p = 0.012 and 71.4% vs. 75.7%, p = 0.029, respectively). The MTHFR 677CC/1298CC, 677CT/1298AA, and 677CT/1298AC genotypes had the highest GQE rates.

CONCLUSIONS

MTHFR 677TT genotype, which had the lowest enzymatic activity, had the lowest oocyte maturation rate. The combined MTHFR 677CC/1298CC, 677CT/1298AA, and 677CT/1298AC genotypes with intermediate enzyme activities had higher GQE rates. However, no differences were observed in the transplantable embryo rate between MTHFR genotypes.

Cloning, bioinformatics analysis and expression of the cysteine dioxygenase type 1 (CDO1) gene in domestic yak

Introduction

The CDO1 gene is an important gene in the taurine synthesis pathway and has been observed to have high expression in ovaries of female mammals. This study aims to explore the conservation of CDO1 gene in domestic yaks, as well as to examine the fundamental characteristics of CDO1 gene and its expression in female yaks.

Methods

Ovarian samples were collected from yaks in the follicular phase, luteal phase and gestation period in this experiment, and their total RNA and protein were extracted. Then Polymerase Chain Reaction (PCR) and bioinformatics online software were used to clone and analyze the CDO1 gene. The relative expression of CDO1 in yak ovaries was detected by Quantitative Real-time PCR (RT-qPCR) and Western blotting. The distribution and localization of CDO1 protein in ovary were detected by immunohistochemistry.

Results

We have successfully cloned the coding region of CDO1 gene in yak. The results showed that the CDS region of CDO1 gene was 603 bp, encoding 200 amino acids, and was a relatively stable hydrophilic protein. CDO1 is relatively conservative in species evolution. The protein encoded by CDO1 gene does not have a signaling peptide or a transmembrane structure. It is a protein that is not involved in transmembrane transport and is mainly located in the cytoplasm. The secondary structure of the protein is dominated by the random coil. CDO1 is estimated to interact with 10 proteins. The results of RT-qPCR and Western blotting showed that the CDO1 gene exhibited the highest expression in the ovary during the luteal phase and the lowest expression in the ovary during the follicular phase (P < 0.01). The results of immunohistochemistry showed that CDO1 was mainly expressed in granular cells, theca cells and lutein cells of ovarian tissue.

Conclusion

These results suggest that the CDO1 gene has undergone minimal evolutionary changes during the course of animal evolution. The results provide a reference for further investigation of the function of CDO1 gene in reproduction and production in yaks.

MTHFR as a Novel Candidate Marker for Litter Size in Rabbits

Litter size is a significant economic trait during animal reproduction. This current study attempted to decipher whether MTHFR promotes the apoptosis of granulosa cells (GCs) and inhibits their proliferation by investigating the effects of the MTHFR gene using flow cytometry and a Cell Counting Kit-8 (CCK-8) assay. MTHFR is linked with ovarian follicle development in the reproductive performance of 104 female New Zealand rabbits. We observed that MTHFR could regulate the mRNA of follicular development-related genes (TIMP1, CITED1, FSHR, GHR, HSD17B1, and STAR) with a qRT-PCR, and we observed the protein expression of CITED1 and GHR using a western blot (WB) analysis. The dual luciferase activity assays helped identify the core promoter region of the MTHFR gene, and the polymorphism of the MTHFR promoter region was studied using Sanger sequencing. The results indicated four single nucleotide polymorphisms (SNPs) within the core promoter region, among which the g.-680C>A locus was significantly associated with both the total and alive litter sizes. Additionally, the CC genotype was associated with the largest total and alive litter sizes, compared to the CA and AA genotypes (p < 0.05). In conclusion, this study investigated the effects of MTHFR on ovarian granulosa cells and its association with selected reproductive parameters in rabbits. The results provide a theoretical foundation for the use of MTHFR as a molecular marker in rabbits.

Genome-wide profiling of histone H3K4me3 and H3K27me3 modifications in individual blastocysts by CUT&Tag without a solid support (NON-TiE-UP CUT&Tag)

Individual analysis of the epigenome of preimplantation embryos is useful for characterizing each embryo and for investigating the effects of environmental factors on their epigenome. However, it is difficult to analyze genome-wide epigenetic modifications, especially histone modifications, in a large number of single embryos due to the small number of cells and the complexity of the analysis methods. To solve this problem, we further modified the CUT&Tag method, which can analyze histone modifications in a small number of cells, such that the embryo is handled as a cell mass in the reaction solutions in the absence of the solid-phase magnetic beads that are used for antibody and enzyme reactions in the conventional method (NON-TiE-UP CUT&Tag; NTU-CAT). By using bovine blastocysts as a model, we showed that genome-wide profiles of representative histone modifications, H3K4me3 and H3K27me3, could be obtained by NTU-CAT that are in overall agreement with the conventional chromatin immunoprecipitation-sequencing (ChIP-seq) method, even from single embryos. However, this new approach has limitations that require attention, including false positive and negative peaks and lower resolution for broad modifications. Despite these limitations, we consider NTU-CAT a promising replacement for ChIP-seq with the great advantage of being able to analyze individual embryos.

5,10-Methylenetetrahydrofolate reductase becomes phosphorylated during meiotic maturation in mouse oocytes

The enzyme 5,10-methylenetetrahydrofolate reductase (MTHFR) links the folate cycle that produces one-carbon units with the methionine cycle that converts these into S-adenosylmethionine (SAM), the universal methyl donor for almost all methyltransferases. Previously, MTHFR has been shown to be regulated by phosphorylation, which suppresses its activity. SAM levels have been shown to increase substantially soon after initiation of meiotic maturation of the mouse germinal vesicle (GV) stage oocyte and then decrease back to their original low level in mature second meiotic metaphase (MII) eggs. As MTHFR controls the entry of one-carbon units into the methionine cycle, it is a candidate regulator of the SAM levels in oocytes and eggs. Mthfr transcripts are expressed in mouse oocytes and preimplantation embryos and MTHFR protein is present at each stage. In mature MII eggs, the apparent molecular weight of MTHFR was increased compared with GV oocytes, which we hypothesized was due to increased phosphorylation. The increase in apparent molecular weight was reversed by treatment with lambda protein phosphatase (LPP), indicating that MTHFR is phosphorylated in MII eggs. In contrast, LPP had no effect on MTHFR from GV oocytes, 2-cell embryos, or blastocysts. MTHFR was progressively phosphorylated after initiation of meiotic maturation, reaching maximal levels in MII eggs before decreasing again after egg activation. As phosphorylation suppresses MTHFR activity, it is predicted that MTHFR becomes inactive during meiotic maturation and is minimally active in MII eggs, which is consistent with the reported changes in SAM levels during mouse oocyte maturation.

Comparative analysis of histone H3K27me3 modifications between blastocysts and somatic tissues in cattle

Epigenetic modifications established in the early developmental stages can have long-term consequences throughout life. This concept encompasses the possibility of controlling livestock health and diseases by epigenetic regulation during early development. To explore the candidates of epigenetic modifications in early embryos that might exert long-lasting effects in adulthood, we aimed to obtain genome-wide histone H3 lysine 27 trimethylation (H3K27me3) profiles of bovine blastocysts and compare these data with those from adult somatic tissues in order to extract common and typical features between them. Bovine blastocysts were produced in vitro and subjected to chromatin immunoprecipitation-sequencing analysis of H3K27me3. Comparative analysis of the blastocyst-derived H3K27me3 profile performed using publicly available data from adult muscle, fat, and liver tissues revealed that (1) blastocyst-specific modifications against somatic tissues were enriched in immune function-related genes, (2) somatic modifications "sieved" by blastocyst modifications were enriched in biological processes in tissue-specific trends, (3) the modifications common in blastocyst and each somatic tissue were largely overlapped and enriched in developmentally important genes, including homeobox and imprinted genes. The results of this study produced a genome-wide H3K27me3 profile of bovine blastocysts and revealed its common and typical features in relation to the profiles of adult somatic tissues.

Choline acts during preimplantation development of the bovine embryo to program postnatal growth and alter muscle DNA methylation

The preimplantation period of embryonic development can be a key window for programming of postnatal development because extensive epigenetic remodeling occurs during this time. It was hypothesized that modification of one-carbon metabolism of the bovine embryo by addition of the methyl-donor choline to culture medium would change postnatal phenotype through epigenetic modification. Embryos produced in vitro were cultured with 1.8 mM choline chloride or control medium. Blastocysts were transferred into females and pregnancy outcomes and postnatal phenotype of the resultant calves determined. Exposure of embryos to choline increased gestation length and calf birth weight. Calves derived from choline-treated embryos were also heavier at weaning and had increased ratio of body weight to hip height than control calves. Choline altered muscle DNA methylation of calves 4 months after birth. A total of 670 of the 8149 CpG examined were differentially methylated, with the predominant effect of choline being hypomethylation. Among the genes associated with differentially methylated CpG were ribosomal RNAs and genes in AMPK, mTOR, integrin, and BEX2 canonical pathways and cellular functions involved in growth and proliferation. Results demonstrate that provision of the methyl-donor choline to the preimplantation embryo can alter its developmental program to increase gestation length, birth weight, and weaning weight and cause postnatal changes in muscle DNA methylation including those associated with genes related to anabolic processes and cellular growth. The importance of the nutritional status of the embryo with respect to one-carbon metabolism for ensuring health and well-being after birth is emphasized by these observations.

MTHFR (methylenetetrahydrofolate reductase: EC 1.5.1.20) SNPs (single-nucleotide polymorphisms) and homocysteine in patients referred for investigation of fertility

Purpose

MTHFR, one of the major enzymes in the folate cycle, is known to acquire single-nucleotide polymorphisms that significantly reduce its activity, resulting in an increase in circulating homocysteine. Methylation processes are of crucial importance in gametogenesis, involved in the regulation of imprinting and epigenetic tags on DNA and histones. We have retrospectively assessed the prevalence of MTHFR SNPs in a population consulting for infertility according to gender and studied the impact of the mutations on circulating homocysteine levels.

Methods

More than 2900 patients having suffered at least two miscarriages (2 to 9) or two failed IVF/ICSI (2 to 10) attempts were included for analysis of MTHFR SNPs C677T and A1298C. Serum homocysteine levels were measured simultaneously.

Results

We observed no difference in the prevalence of different genetic backgrounds between men and women; only 15% of the patients were found to be wild type. More than 40% of the patients are either homozygous for one SNP or compound heterozygous carriers. As expected, the C677T SNP shows the greatest adverse effect on homocysteine accumulation. The impact of MTHFR SNPs on circulating homocysteine is different in men than in women.

Conclusions

Determination of MTHFR SNPs in both men and women must be seriously advocated in the presence of long-standing infertility; male gametes, from MTHFR SNPs carriers, are not exempted from exerting a hazardous impact on fertility. Patients should be informed of the pleiotropic medical implications of these SNPs for their own health, as well as for the health of future children.

Comparative analysis of histone H3K4me3 modifications between blastocysts and somatic tissues in cattle

Epigenetic changes induced in the early developmental stages by the surrounding environment can have not only short-term but also long-term consequences throughout life. This concept constitutes the “Developmental Origins of Health and Disease” (DOHaD) hypothesis and encompasses the possibility of controlling livestock health and diseases by epigenetic regulation during early development. As a preliminary step for examining changes of epigenetic modifications in early embryos and their long-lasting effects in fully differentiated somatic tissues, we aimed to obtain high-throughput genome-wide histone H3 lysine 4 trimethylation (H3K4me3) profiles of bovine blastocysts and to compare these data with those from adult somatic tissues in order to extract common and typical features between these tissues in terms of H3K4me3 modifications. Bovine blastocysts were produced in vitro and subjected to chromatin immunoprecipitation-sequencing analysis of H3K4me3. Comparative analysis of the blastocyst-derived H3K4me3 profile with publicly available data from adult liver and muscle tissues revealed that the blastocyst profile could be used as a “sieve” to extract somatic tissue-specific modifications in genes closely related to tissue-specific functions. Furthermore, principal component analysis of the level of common modifications between blastocysts and somatic tissues in meat production-related and imprinted genes well characterized inter- and intra-tissue differences. The results of this study produced a referential genome-wide H3K4me3 profile of bovine blastocysts within the limits of their in vitro source and revealed its common and typical features in relation to the profiles of adult tissues.

Methylation: An Ineluctable Biochemical and Physiological Process Essential to the Transmission of Life

Methylation is a universal biochemical process which covalently adds methyl groups to a variety of molecular targets. It plays a critical role in two major global regulatory mechanisms, epigenetic modifications and imprinting, via methyl tagging on histones and DNA. During reproduction, the two genomes that unite to create a new individual are complementary but not equivalent. Methylation determines the complementary regulatory characteristics of male and female genomes. DNA methylation is executed by methyltransferases that transfer a methyl group from S-adenosylmethionine, the universal methyl donor, to cytosine residues of CG (also designated CpG). Histones are methylated mainly on lysine and arginine residues. The methylation processes regulate the main steps in reproductive physiology: gametogenesis, and early and late embryo development. A focus will be made on the impact of assisted reproductive technology and on the impact of endocrine disruptors (EDCs) via generation of oxidative stress.