NSUN5 is essential for proper cell proliferation and differentiation of mouse preimplantation embryos.

In brief: Proper early embryonic development in mammals relies on precise cellular signaling pathways. This study reveals that NSUN5 is crucial for the regulation of the Hippo pathway, ensuring normal proliferation and differentiation in mouse preimplantation embryos. Abstract: NOL1/NOP2/Sun domain family, member 5 (NSUN5) is an enzyme belonging to the 5-methylcytosine (m5C) writer family that modifies rRNA and mRNA. Our data revealed an upregulation of Nsun5 at the two-cell stage of mouse preimplantation development, suggesting its significance in early embryonic development. Given m5C's important role in stabilizing rRNA and mRNA and the Hippo signaling pathway's critical function in lineage segregation during embryogenesis, we hypothesized that NSUN5 controls cell differentiation by regulating the expression of components of the Hippo signaling pathway in mouse early embryos. To examine this hypothesis, we employed Nsun5-specific small interfering RNAs for targeted gene silencing in mouse preimplantation embryos. Nsun5 knockdown resulted in significant developmental impairments including reduced blastocyst formation, smaller size of blastocysts, and impaired hatching from the zona pellucida. Nsun5 knockdown also led to decreased cell numbers and increased apoptosis in embryos. We also observed diminished nuclear translocation of yes-associated protein 1 (YAP1) in Nsun5 knockdown embryos at the morula stage, indicating disrupted cell differentiation. This disruption was further evidenced by an altered ratio of CDX2-positive to OCT4-positive cells. Furthermore, Nsun5 depletion was found to upregulate the Hippo signaling-related key genes, Lats1 and Lats2 at the morula stage. Our findings underscore the essential role of Nsun5 in early embryonic development by affecting cell proliferation, YAP1 nuclear translocation, and the Hippo pathway.

Analysis of histone H3K4me3 modifications in bovine placenta derived from different calf-production methods.

In ruminants, the overgrowth of offspring produced by in vitro fertilization (IVF) is a common problem. Abnormal epigenetic modifications caused by environmental factors during the early embryonic period are suspected as an aetiology of overgrowth. In this study, we investigated the genome-wide histone H3K4me3 profiles of bovine placentae that play a pivotal role in foetal development and compared their characteristics between artificial insemination (AI)- and IVF-derived samples. Cotyledons were harvested from the placentae obtained at parturition of 5 AI- and 13 IVF-derived calves, and chromatin immunoprecipitation sequencing was performed for H3K4me3. We confirmed no significant maternal tissue contamination in the samples we used. The revealed H3K4me3 profiles reflected the general characteristics of the H3K4me3 modification, which is abundantly distributed in the promoter region of active genes. By extracting common modifications from multiple samples, the genes involved in placenta-specific biological processes could be enriched. Comparison with the H3K4me3 modifications of blastocyst samples was also effective for enriching the placenta-specific features. Principal component analysis suggested the presence of differential H3K4me3 modifications in AI- and IVF-derived samples. The genes contributing to the difference were related to the developmental biological processes. Imprinted genes such as BEGAIN, ZNF215 and DLX5 were among the extracted genes. Principal component and discriminant analyses using only male samples categorized the samples into three groups based on foetal weight and calf-production methods. To our knowledge, this is the first study to profile the genome-wide histone modifications of bovine foetal placentae and reveal their differential characteristics between different calf-production methods.

Chimeric PRMT6 protein produced by an endogenous retrovirus promoter regulates cell fate decision in mouse preimplantation embryos†.

Murine endogenous retrovirus with leucine tRNA primer, also known as MERVL, is expressed during zygotic genome activation in mammalian embryos. Here we show that protein arginine N-methyltransferase 6 (Prmt6) forms a chimeric transcript with MT2B2, one of the long terminal repeat sequences of murine endogenous retrovirus with leucine tRNA primer, and is translated into an elongated chimeric protein (PRMT6MT2B2) whose function differs from that of the canonical PRMT6 protein (PRMT6CAN) in mouse preimplantation embryos. Overexpression of PRMT6CAN in fibroblast cells increased asymmetric dimethylation of the third arginine residue of both histone H2A (H2AR3me2a) and histone H4 (H4R3me2a), while overexpression of PRMT6MT2B2 increased only H2AR3me2a. In addition, overexpression of PRMT6MT2B2 in one blastomere of mouse two-cell embryos promoted cell proliferation and differentiation of the blastomere into epiblast cells at the blastocyst stage, while overexpression of PRMT6CAN repressed cell proliferation. This is the first report of the translation of a chimeric protein (PRMT6MT2B2) in mouse preimplantation embryos. Our results suggest that analyzing chimeric transcripts with murine endogenous retrovirus with leucine tRNA primer will provide insight into the relationship between zygotic genome activation and subsequent intra- and extra-cellular lineage determination.

Evaluating histone modification analysis of individual preimplantation embryos.

BACKGROUND: We previously reported a modification of the CUT&Tag method (NTU-CAT) that allows genome-wide histone modification analysis in individual preimplantation embryos. In the present study, NTU-CAT was further simplified by taking advantage of the Well-of-the-Well (WOW) system, which enables the processing of multiple embryos in a shorter time with less reagent and cell loss during the procedure (WOW-CUT&Tag, WOW-CAT). RESULTS: WOW-CAT allowed histone modification profiling from not only a single blastocyst but also from a portion of it. WOW-CAT generated similar H3K4me3 profiles as NTU-CAT, but they were closer to the profiles produced by chromatin immunoprecipitation-sequencing, such as a valley-like trend and relatively lower false positive rates, indicating that WOW-CAT may attenuate the bias of Tn5 transposase to cut open chromatin regions. Simultaneous WOW-CAT of two halves of single blastocysts was conducted to analyze two different histone modifications (H3K4me3 and H3K27ac) within the same embryo. Furthermore, trophectoderm cells were biopsied and subjected to WOW-CAT in anticipation of preimplantation diagnosis of histone modifications. WOW-CAT allowed the monitoring of epigenetic modifications in the main body of the embryo. For example, analysis of H3K4me3 modifications of XIST and DDX3Y in trophectoderm biopsies could be used to sex embryos in combination with quantitative PCR, but without the need for deep sequencing. CONCLUSIONS: These results suggest the applicability of WOW-CAT for flexible epigenetic analysis of individual embryos in preimplantation epigenetic diagnosis.

MYC-MAX heterodimerization is essential for the induction of major zygotic genome activation and subsequent preimplantation development.

In mouse preimplantation development, zygotic genome activation (ZGA), which synthesizes new transcripts in the embryo, begins in the S phase at the one-cell stage, with major ZGA occurring especially at the late two-cell stage. Myc is a transcription factor expressed in parallel with ZGA, but its direct association with major ZGA has not been clarified. In this study, we found that developmental arrest occurs at the two-cell stage when mouse embryos were treated with antisense oligonucleotides targeting Myc or MYC-specific inhibitors from the one-cell stage. To identify when MYC inhibition affects development, we applied time-limited inhibitor treatment and found that inhibition of MYC at the one-cell, four-cell, and morula stages had no effect on preimplantation development, whereas inhibitor treatment at the two-cell stage arrested development at the two-cell stage. Furthermore, transcriptome analysis revealed that when MYC function was inhibited, genes expressed in the major ZGA phase were suppressed. These results suggest that MYC is essential for the induction of major ZGA and subsequent preimplantation development. Revealing the function of MYC in preimplantation development is expected to contribute to advances in assisted reproductive technology.

A more accurate analysis of maternal effect genes by siRNA electroporation into mouse oocytes.

Maternal RNA and proteins accumulate in mouse oocytes and regulate initial developmental stages. Sperm DNA combines with protamine, which is exchanged after fertilization with maternal histones, including H3.3; however, the effect of H3.3 on development post-fertilization remains unclear. Herein, we established an electroporation method to introduce H3.3 siRNA into germinal vesicle (GV)-stage oocytes without removing cumulus cells. Oocyte-attached cumulus cells need to be removed during the traditional microinjection method; however, we confirmed that artificially removing cumulus cells from oocytes reduced fertilization rates, and oocytes originally free of cumulus cells had reduced developmental competence. On introducing H3.3 siRNA at the GV stage, H3.3 was maintained in the maternal pronucleus and second polar body but not in the paternal pronucleus, resulting in embryonic lethality after fertilization. These findings indicate that H3.3 protein was not incorporated into the paternal pronucleus, as it was repeatedly translated and degraded over a relatively short period. Conversely, H3.3 protein incorporated into the maternal genome in the GV stage escaped degradation and remained in the maternal pronucleus after fertilization. This new method of electroporation into GV-stage oocytes without cumulus cell removal is not skill-intensive and is essential for the accurate analysis of maternal effect genes.

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.

H4K20 monomethylation inhibition causes loss of genomic integrity in mouse preimplantation embryos.

Maintaining genomic integrity in mammalian early embryos, which are deficient in DNA damage repair, is critical for normal preimplantation and subsequent development. Abnormalities in DNA damage repair in preimplantation embryos can cause not only developmental arrest, but also diseases such as congenital disorders and cancers. Histone H4 lysine 20 monomethylation (H4K20me1) is involved in DNA damage repair and regulation of gene expression. However, little is known about the role of H4K20me1 during mouse preimplantation development. In this study, we revealed that H4K20me1 mediated by SETD8 is involved in maintaining genomic integrity. H4K20me1 was present throughout preimplantation development. In addition, reduction in the level of H4K20me1 by inhibition of SETD8 activity or a dominant-negative mutant of histone H4 resulted in developmental arrest at the S/G2 phase and excessive accumulation of DNA double-strand breaks. Together, our results suggest that H4K20me1, a type of epigenetic modification, is associated with the maintenance of genomic integrity and is essential for preimplantation development. A better understanding of the mechanisms involved in maintaining genome integrity during preimplantation development could contribute to advances in reproductive medicine and technology.

Membrane fusogenic high-density lipoprotein nanoparticles.

Membrane fusion under mildly acidic pH occurs naturally during viral infection in cells and has been exploited in the field of nanoparticle-mediated drug delivery to circumvent endosomal entrapment of the cargo. Herein, we aimed to confer virus-like fusogenic activity to HDL in the form of a ca. 10-nm disc comprising a discoidal lipid bilayer and two copies of a lipid-binding protein at the edge. A series of HDL mutants were prepared with a mixture of three lipids and a cell-penetrating peptide (TAT, penetratin, or Arg8) fused to the protein. In a lipid-mixing assay with anionic liposomes at pH 5.5, one HDL mutant showed the fusogenic activity higher than known fusogenic liposomes. In live mammalian cells, this HDL mutant showed high plasma membrane-binding activity in the presence of serum independent of pH. In the absence of serum, a mildly acidic pH dependency for binding to the plasma membrane and the subsequent lipid mixing between them was observed for this mutant. We propose a novel strategy to develop HDL-based drug carriers by taking advantage of the HDL lipid/protein composite structure.

Oocyte-specific gene Oog1 suppresses the expression of spermatogenesis-specific genes in oocytes.

Oog1, an oocyte-specific gene that encodes a protein of 425 amino acids, is present in five copies on mouse chromosomes 4 and 12. In mouse oocytes, Oog1 mRNA expression begins at embryonic day 15.5 and almost disappears by the late two-cell stage. Meanwhile, OOG1 protein is detectable in oocytes in ovarian cysts and disappears by the four-cell stage; the protein is transported to the nucleus in late one-cell to early two-cell stage embryos. In this study, we examined the role of Oog1 during oogenesis in mice. Oog1 RNAi-transgenic mice were generated by expressing double-stranded hairpin Oog1 RNA, which is processed into siRNAs targeting Oog1 mRNA. Quantitative RT-PCR revealed that the amount of Oog1 mRNA was dramatically reduced in oocytes obtained from Oog1-knockdown mice, whereas the abundance of spermatogenesis-associated transcripts (Klhl10, Tekt2, Tdrd6, and Tnp2) was increased in Oog1 knockdown ovaries. Tdrd6 is involved in the formation of the chromatoid body, Tnp2 contributes to the formation of sperm heads, Tekt2 is required for the formation of ciliary and flagellar microtubules, and Klhl10 plays a key role in the elongated sperm differentiation. These results indicate that Oog1 down-regulates the expression of spermatogenesis-associated genes in female germ cells, allowing them to develop normally into oocytes.

Ultrafast and broadband frequency chirp signal generation using a high-extinction-ratio optical modulator.

We successfully demonstrate ultrafast frequency sweep signal generation using the double-sideband suppressed carrier modulation technique with a high-extinction-ratio optical modulator that helps realize clear signals with no filters. The resultant sweep rate was achieved at 3.67 × 10(16) Hz/s with an extinction ratio above 25 dB, which corresponds to a bandwidth of 11 GHz with a pulse duration of 300 ns.