Cell Stage Research Articles

The splicing factor SF3B1 is essential for proper alternative splicing and zygotic genome activation in early porcine embryos

Alternative splicing (AS) is a pivotal posttranscriptional regulatory mechanism that is involved in embryonic development. However, the roles of AS in specific developmental events, especially the zygotic genome activation (ZGA) of porcine early embryos, remain unclear. In this study, we demonstrated that alternative splicing events (ASEs) were most prevalent in mammalian embryos during ZGA and that skipped exons were the predominant splicing pattern. When splicing factor 3B subunit 1 (SF3B1) was disrupted by the inhibitor pladienolide B (PlaB), we observed that porcine embryos were markedly arrested at the 4-cell stage. Concurrently, the main ZGA genes, namely, DPPA2, EIF6, and SORD, underwent aberrant splicing indicative of the failure of ZGA. Moreover, embryonic metabolic homeostasis was significantly disrupted at the 4-cell stage by SF3B1 inhibition, resulting in increases in the LDHA/LDHB ratio and lactate levels. Interestingly, the levels of the histone lactylation modifications pan-Kla and H4K5la also increased. Our findings enhance our understanding of early mammalian embryonic development, reveal the crucial role of porcine early embryogenesis, and help to resolve reproductive difficulties related to embryonic development.

Glyphosate formulations cause mortality and diverse sublethal defects during embryonic development of the amphibian Xenopuslaevis

The human impact on environmental landscapes, such as land use, climate change or pollution, is threatening global biodiversity and ecosystems maintenance. Pesticides like the herbicide glyphosate have garnered considerable attention due to their well-documented harmful effects on non-target species. During application, the active ingredient glyphosate is utilized in various formulations, each containing different additive adjuvants. However, the possible effects of these formulations on amphibians - the group with the highest decline rates among vertebrates - remain largely unknown.Therefore, the present study investigated the effects of four glyphosate formulations (Glyphosat TF, Durano TF, Helosate 450 TF, Kyleo) on the embryonic development of the model organism Xenopus laevis (South African clawed frog). Embryos at the 2-cell stage were exposed to various concentrations of glyphosate formulations (glyphosate: 0.01–100 mg/L), and mortality as well as sublethal effects on different organs and tissues were analyzed. The results indicated that the formulations had different effects, particularly on the mortality of Xenopus laevis embryos. At sublethal concentrations, the formulations altered the embryos' external appearance, leading to malformations such as reduced eye and head size. In addition, exposure to formulations impaired heart morphology and function, and the expression of heart-specific genes was altered at a molecular level.Our results confirmed that glyphosate formulations had a stronger effect on Xenopus laevis embryogenesis than pure glyphosate. Therefore, it is crucial to evaluate the active ingredient and the co-formulations independently, as well as the combined, commercially available products, during pesticide risk assessments and renewal procedures of agrochemicals. The severe global decline of amphibians, partly due to herbicide use, highlights the need for strict and efficient monitoring of environmental pesticide loads and application areas.

Fertilization and developmental competence of in vitro fertilized embryos from C57BL/6J mice of different ages and the impact of vitrification.

Prepubertal animals are often preferred as sources of oocytes for assisted reproductive technologies (ARTs) in laboratory mice, but the normality and developmental competence of these oocytes remain controversial. This study systematically examined in vitro fertilization competence, embryo development, and fetal development after embryo transfer (ET) using oocytes from C57BL/6J mice aged 3 to 10 weeks. Oocytes were collected from superovulated females, fertilized, and cultured in vitro for 96 h or transferred at 2-cell stage to recipient females. Additionally, fetal development was compared between unfrozen and frozen-thawed in vitro-fertilized 2-cell embryos across different age groups. The number of ovulated oocytes per animal decreased with age, while the percentage of morphologically normal oocytes was highest in 3-week-old mice (99%) compared to older ages (70-86%, P < 0.05). Although fertilization percentages were consistently high (≥ 97%), blastocyst development in vitro, the nuclear counts of blastocysts and fetal development after ET were lowest for embryos from 3-week-old mice. Development of frozen-thawed embryos to fetuses was significantly reduced compared to unfrozen embryos in all age groups, except for those from 10-week-old mice. These findings suggest that oocytes from prepubertal mice, particularly from 3-week-old mice, are less developmentally competent than those from older mice. Therefore, the age of animals for oocyte source should be carefully considered based on the specific requirements of the research or ART applications.

Hybrid incompatibility emerges at the one-cell stage in interspecies Caenorhabditis embryos.

Intrinsic reproductive isolation occurs when genetic differences between populations disrupt the development of hybrid organisms, preventing gene flow and enforcing speciation. 1-4 While prior studies have examined the genetic origins of hybrid incompatibility, 5-18 the effects of incompatible factors on development remain poorly understood. Here, we investigate the mechanistic basis of hybrid incompatibility in Caenorhabditis nematodes by capitalizing on the ability of C. brenneri females to produce embryos after mating with males from several other species. Contrary to expectations, hybrid incompatibility was evident immediately after fertilization, suggesting that post-fertilization barriers to hybridization originate from physical incompatibility between sperm and oocyte-derived factors rather than from zygotic transcription, which starts after the 4-cell stage. 19-22 Sperm deliver chromatin, which expands to form a pronucleus, and a pair of centrioles, which form centrosomes that attach to the sperm-derived pronucleus and signal to establish the embryo's anterior-posterior axis. 23,24 In C. brenneri oocytes fertilized with C. elegans sperm, sperm pronuclear expansion was compromised, frequent centrosome detachment was observed, and cortical polarity was disrupted. Live imaging revealed that defective polar body extrusion contributes to defects in mitotic spindle morphology. C. brenneri oocytes fertilized with C. remanei or C. sp. 48 sperm showed similar defects, and their severity and frequency increased with phylogenetic distance. Defective expansion of the sperm-derived pronucleus and unreliable polar body extrusion immediately after fertilization generally underlie the inviability of hybrid embryos in this clade. These results indicate that physical mismatches between sperm and oocyte-derived structures may be a primary mechanism of hybrid incompatibility.

The kinetics of nucleolar precursor bodies clustering at the pronuclei interface: Positive correlations with the morphokinetic characteristics of cleaving embryos and euploidy in preimplantation genetic testing programs

Objective: This study investigated potential relationships between the kinetics of nucleolar precursor bodies (NPBs) in the pronucleus and developmental morphokinetics and euploidy in human preimplantation genetic testing for aneuploidy (PGT-A) cycles.Methods: The morphokinetic analysis of 200 blastocysts obtained from 53 PGT-A cycles was performed retrospectively in a time-lapse incubator. At the time of pronuclear breakdown (PNBD), we categorized the blastocysts into two groups based on the kinetic degree of clustering NPBs at the interface of the two pronuclei: clustered NPBs (CL) and non-clustered NPBs (NCL). We then compared morphokinetic parameters, abnormal behavioral events, and the rate of aneuploidy between the two groups.Results: Pronuclear fading and the first cleavage occurred earlier in the NCL group than in the CL group. However, the initiation of blastocyst formation and blastocyst expansion was delayed in the NCL group relative to the CL group. No differences were found in the rate of abnormal cleavage events, such as multinucleation at the 2-cell stage, direct cleavage from one to three cells, and from two to five cells between the CL and NCL groups. However, the fragmentation rate at the 8-cell stage was higher in the NCL group than in the CL group (10.3% vs. 1.9%, p&lt;0.05). Additionally, the euploid rate in the CL group was significantly higher than in the NCL group (37.9% vs. 12.4%, p&lt;0.05).Conclusion: These results demonstrate the effectiveness of combining NPB clustering at PNBD with morphokinetics as a parameter for selecting embryos with higher developmental potential in in vitro fertilization.

The effect of male factors on embryo morphokinetics: a retrospective analysis of 2726 blastocysts.

Male infertility may influence fertilization rates, embryo morphology, and implantation rates in in vitro fertilization (IVF) cycles. Oocyte competence plays a major role in embryo development, but there is a limited understanding of the connection between sperm quality, embryo development, and morphokinetic parameters using donor oocytes. The study evaluated if sperm quality may influence the morphokinetic parameters in IVF cycles. A retrospective multicentric observational cohort study included 747 ICSI cycles using donor oocytes with fresh or frozen sperm. Embryos were cultured in time-lapse incubators until the blastocyst stage. The population was divided into three groups according to sperm concentration, as control group (> 16 mill/mL), severe oligospermia (0-5 mill/mL), and moderate oligospermia group (5-16 mill/mL). Morphokinetic analysis showed no difference in the time from the 2-cell to 6-cell stage of embryo development. A significant difference was observed on day 3 of embryo development, specifically at the 7-cell stage (t7), severe oligospermia 53.37 ± 9.81, moderate oligospermia 56.95 ± 9.78, and control 55.1 ± 8.85h post-insemination (hpi) (p = 0.024), and 8-cell stage (t8), severe oligospermia 55.41 ± 10.83, moderate oligospermia 61.86 ± 12.38 hpi (p < 0.001), and control 58.61 ± 11.33. Accordingly, the synchrony of the four cleavages going from 4 to 8 cells (s3) was found statistically different among the groups in the severe oligospermia 8.05 ± 9.99, moderate oligospermia 11.66 ± 11.04 hpi, and control 8.55 ± 8.58 (p = 0.009). Morphokinetic time ranges were obtained for t6, t7, t8, and s3 in order to identify the good-quality blastocysts. Poor sperm quality is associated with alterations in morphokinetic parameters on day 3 in IVF cycles with donor oocytes, underlining the important role of spermatozoa during embryo development.

Nuclear instance segmentation and tracking for preimplantation mouse embryos.

For investigations into fate specification and morphogenesis in time-lapse images of preimplantation embryos, automated 3D instance segmentation and tracking of nuclei are invaluable. Low signal-to-noise ratio, high voxel anisotropy, high nuclear density, and variable nuclear shapes can limit the performance of segmentation methods, while tracking is complicated by cell divisions, low frame rates, and sample movements. Supervised machine learning approaches can radically improve segmentation accuracy and enable easier tracking, but they often require large amounts of annotated 3D data. Here we first report a novel mouse line expressing near-infrared nuclear reporter H2B-miRFP720. We then generate a dataset (termed BlastoSPIM) of 3D images of H2B-miRFP720-expressing embryos with ground truth for nuclear instances. Using BlastoSPIM, we benchmark seven convolutional neural networks and identify Stardist-3D as the most accurate instance segmentation method. With our BlastoSPIM-trained Stardist-3D models, we construct a complete pipeline for nuclear instance segmentation and lineage tracking from the 8-cell stage to the end of preimplantation development (>100 nuclei). Finally, we demonstrate BlastoSPIM's usefulness as pre-train data for related problems, both for a different imaging modality and for different model systems.

9233 Sperm-carried IGF2: a Spark Contributing To Embryo Growth And Development

Abstract Disclosure: R. Cannarella: None. O.J. Rando: None. R.A. Condorelli: None. C. Sandrine: None. S. Romano: None. A. Guglielmino: None. Q. Yin: None. H. Gustafsson: None. F. Mancuso: None. C. Bellucci: None. G. Luca: None. S. La Vignera: None. A.E. Calogero: None. Background: Sperm RNAs can regulate early embryo development. A potential key regulator of growth is insulin-like growth factor 2 (IGF2), a highly conserved paternally-imprinted gene involved in cell growth and proliferation that is expressed in human spermatozoa. Animal research supports the positive impact of IGF2-supplemented cultures on embryo quality. However, the role of sperm-carried IGF2 in the early development of the human embryo is unknown. Objective: To study whether sperm-carried IGF2 mRNA influences the morphokinetics of the human embryo. Design: Prospective, uncontrolled, observational pilot study. Setting: University-affiliated fertility center. Subjects: We enrolled 16 patients undergoing assisted reproductive techniques (ART) for idiopathic or male factor infertility and 10 healthy fertile controls with proven paternity. Couples with female factor infertility due to reduced oocyte reserve were excluded, while those with tubal factor or anovulation were included. Main Outcome Measure(s): After clinical use, an aliquot of the sperm samples employed for ART was used to evaluate IGF2 mRNA levels. Embryo kinetics were recorded and correlated with the amount of IGF2 mRNA, correcting for female age, body mass index (BMI), anti-Müllerian hormone (AMH) levels, and oocyte quality. To provide mechanistic insights into the human data, a transcriptome analysis was performed of parthenotes obtained from twelve-week-old superovulated mice injected with Igf2 mRNA plus Gfp mRNA (experimental group, n=20) or Gfp mRNAs (control group, n=20). Pathway enrichment analysis was then performed using g:Profiler g:GOSt and EnrichR. Results: Sperm IGF2 mRNA negatively correlated with time to 2-cell stage (t2), t3, t4, t5, and time to expanded blastocyst (tEB), independently of maternal age, BMI, AMH, and oocyte quality. IGF2 mRNA index &amp;gt;4.9 predicted the ability of the embryo to reach the blastocyst stage at day 5, with a sensitivity of 100% and specificity of 71.6% (AUC 0.845; p&amp;lt;0.001). The distribution of sperm IGF2 levels differs significantly between morphologically good or poor embryos, with the lowest levels more frequently associated with morphologically poor embryos (61.9%) than with good ones (38.1%) (p=0.0091). Furthermore, sperm-derived IGF2 levels were significantly lower in subfertile men compared to fertile controls with proven paternity. Transcriptome analysis of Igf2-injected embryos demonstrated differential expression of 101 genes activating pathways regulating early embryo development. Conclusion: Sperm-carried IGF2 mRNA can support early embryo development, independently of female factors. Larger studies are needed to confirm this finding and to investigate its role as a clinical marker to predict the chances of obtaining blastocysts that can be implanted in infertile couples undergoing ART. Presentation: 6/1/2024

7110 Sperm-carried IGF2: a Spark Contributing To Embryo Growth And Development

Abstract Disclosure: R. Cannarella: None. O.J. Rando: None. R.A. Condorelli: None. C. Sandrine: None. S. Romano: None. A. Guglielmino: None. Q. Yin: None. H. Gustafsson: None. F. Mancuso: None. C. Bellucci: None. G. Luca: None. S. La Vignera: None. A.E. Calogero: None. Background: Sperm RNAs can regulate early embryo development. A potential key regulator of growth is insulin-like growth factor 2 (IGF2), a highly conserved paternally-imprinted gene involved in cell growth and proliferation that is expressed in human spermatozoa. Animal research supports the positive impact of IGF2-supplemented cultures on embryo quality. However, the role of sperm-carried IGF2 in the early development of the human embryo is unknown. Objective: To study whether sperm-carried IGF2 mRNA influences the morphokinetics of the human embryo. Design: Prospective, uncontrolled, observational pilot study. Setting: University-affiliated fertility center. Subjects: We enrolled 16 patients undergoing assisted reproductive techniques (ART) for idiopathic or male factor infertility and 10 healthy fertile controls with proven paternity. Couples with female factor infertility due to reduced oocyte reserve were excluded, while those with tubal factor or anovulation were included. Main Outcome Measure(s): After clinical use, an aliquot of the sperm samples employed for ART was used to evaluate IGF2 mRNA levels. Embryo kinetics were recorded and correlated with the amount of IGF2 mRNA, correcting for female age, body mass index (BMI), anti-Müllerian hormone (AMH) levels, and oocyte quality. To provide mechanistic insights into the human data, a transcriptome analysis was performed of parthenotes obtained from twelve-week-old superovulated mice injected with Igf2 mRNA plus Gfp mRNA (experimental group, n=20) or Gfp mRNAs (control group, n=20). Pathway enrichment analysis was then performed using g:Profiler g:GOSt and EnrichR. Results: Sperm IGF2 mRNA negatively correlated with time to 2-cell stage (t2), t3, t4, t5, and time to expanded blastocyst (tEB), independently of maternal age, BMI, AMH, and oocyte quality. IGF2 mRNA index &amp;gt;4.9 predicted the ability of the embryo to reach the blastocyst stage at day 5, with a sensitivity of 100% and specificity of 71.6% (AUC 0.845; p&amp;lt;0.001). The distribution of sperm IGF2 levels differs significantly between morphologically good or poor embryos, with the lowest levels more frequently associated with morphologically poor embryos (61.9%) than with good ones (38.1%) (p=0.0091). Furthermore, sperm-derived IGF2 levels were significantly lower in subfertile men compared to fertile controls with proven paternity. Transcriptome analysis of Igf2-injected embryos demonstrated differential expression of 101 genes activating pathways regulating early embryo development. Conclusion: Sperm-carried IGF2 mRNA can support early embryo development, independently of female factors. Larger studies are needed to confirm this finding and to investigate its role as a clinical marker to predict the chances of obtaining blastocysts that can be implanted in infertile couples undergoing ART. Presentation: 6/1/2024

7110 Sperm-carried IGF2: a Spark Contributing To Embryo Growth And Development

Abstract Disclosure: R. Cannarella: None. O.J. Rando: None. R.A. Condorelli: None. C. Sandrine: None. S. Romano: None. A. Guglielmino: None. Q. Yin: None. H. Gustafsson: None. F. Mancuso: None. C. Bellucci: None. G. Luca: None. S. La Vignera: None. A.E. Calogero: None. Background: Sperm RNAs can regulate early embryo development. A potential key regulator of growth is insulin-like growth factor 2 (IGF2), a highly conserved paternally-imprinted gene involved in cell growth and proliferation that is expressed in human spermatozoa. Animal research supports the positive impact of IGF2-supplemented cultures on embryo quality. However, the role of sperm-carried IGF2 in the early development of the human embryo is unknown. Objective: To study whether sperm-carried IGF2 mRNA influences the morphokinetics of the human embryo. Design: Prospective, uncontrolled, observational pilot study. Setting: University-affiliated fertility center. Subjects: We enrolled 16 patients undergoing assisted reproductive techniques (ART) for idiopathic or male factor infertility and 10 healthy fertile controls with proven paternity. Couples with female factor infertility due to reduced oocyte reserve were excluded, while those with tubal factor or anovulation were included. Main Outcome Measure(s): After clinical use, an aliquot of the sperm samples employed for ART was used to evaluate IGF2 mRNA levels. Embryo kinetics were recorded and correlated with the amount of IGF2 mRNA, correcting for female age, body mass index (BMI), anti-Müllerian hormone (AMH) levels, and oocyte quality. To provide mechanistic insights into the human data, a transcriptome analysis was performed of parthenotes obtained from twelve-week-old superovulated mice injected with Igf2 mRNA plus Gfp mRNA (experimental group, n=20) or Gfp mRNAs (control group, n=20). Pathway enrichment analysis was then performed using g:Profiler g:GOSt and EnrichR. Results: Sperm IGF2 mRNA negatively correlated with time to 2-cell stage (t2), t3, t4, t5, and time to expanded blastocyst (tEB), independently of maternal age, BMI, AMH, and oocyte quality. IGF2 mRNA index &amp;gt;4.9 predicted the ability of the embryo to reach the blastocyst stage at day 5, with a sensitivity of 100% and specificity of 71.6% (AUC 0.845; p&amp;lt;0.001). The distribution of sperm IGF2 levels differs significantly between morphologically good or poor embryos, with the lowest levels more frequently associated with morphologically poor embryos (61.9%) than with good ones (38.1%) (p=0.0091). Furthermore, sperm-derived IGF2 levels were significantly lower in subfertile men compared to fertile controls with proven paternity. Transcriptome analysis of Igf2-injected embryos demonstrated differential expression of 101 genes activating pathways regulating early embryo development. Conclusion: Sperm-carried IGF2 mRNA can support early embryo development, independently of female factors. Larger studies are needed to confirm this finding and to investigate its role as a clinical marker to predict the chances of obtaining blastocysts that can be implanted in infertile couples undergoing ART. Presentation: 6/1/2024

Genomic and Transcriptional Analysis of the Necroptosis Pathway Elements RIPK and MLKL in Sea Cucumber, Holothuria leucospilota.

Background: Receptor-interacting protein kinases (RIPKs) and mixed-lineage kinase domain-like protein (MLKL) are crucial in regulating innate immune responses and cell death signaling (necroptosis and apoptosis), and are potential candidates for genetic improvement in breeding programs. Knowledge about the RIPK family and MLKL in sea cucumber remains limited. Methods: We searched the genomes of sea cucumber Holothuria leucospilota for genes encoding RIPKs and MLKL, performed phylogenetic tree, motif and functional domain analyses, and examined tissue distribution and embryonic development patterns using qPCR. Results: RIPK5 (Hl-RIPK5), RIPK7 (Hl-RIPK7) and MLKL (Hl-MLKL) were identified in sea cucumber H. leucospilota. Hl-RIPK5 and Hl-RIPK7 were mainly expressed in coelomocytes, suggesting that they play a role in innate immunity, whereas Hl-MLKL exhibited relatively low expression across tissues. During embryonic development, Hl-MLKL was highly expressed from the 2-cell stage to the morula stage, while Hl-RIPK5 and Hl-RIPK7 were primarily expressed after the morula stage, indicating different roles in embryonic development. In primary coelomocytes, Hl-RIPK5 transcriptional activity was significantly depressed by LPS, poly(I:C), or pathogen Vibrio harveyi. Hl-RIPK7 expression levels were unchanged following the same challenges. Hl-MLKL mRNA levels were significantly decreased with poly(I:C) or V. harveyi, but did not change with LPS. Conclusions: These findings provide valuable insights into the evolutionary tree and characterization of RIPK and MLKL genes in sea cucumber, contributing to the broader understanding of the RIPK gene family and MLKL in ancient echinoderms.

Genome-wide profiling the epigenetic landscape of histone variant TH2B in murine oocytes and pre-implantation embryos.

The histone variant TH2B, enriched in oocytes, sperm, and early embryos, decreases as embryos differentiate into pre-gastrula stages. Despite its presence, the role of TH2B in epigenetic reprogramming during early embryonic development remains largely under-researched. Our study employed ultra-low-input ChIP-seq (ULI-ChIP) to analyze the genome-wide distribution of TH2B in MII oocytes and early embryos. We found that TH2B is enriched in the chromatin of oocytes and 2-cell stage embryos but becomes less prevalent after the 2-cell stage. Correlation analysis revealed that the TH2B chromatin patterns in sperm and preimplantation embryos are more similar to each other than to those in MII oocytes. Gene ontology (GO) analysis of TH2B-occupied loci linked them to various developmental processes, including oogenesis, fertilization, chromatin modification, and transcription regulation. The study also identified a strong association of TH2B with specific transposable elements (TEs), particularly long terminal repeats (LTRs), which are known to regulate preimplantation development. Additionally, early embryos showed H3K9me3 marks at TH2B-bound loci. TH2B exhibited strong correlations with H2A.Z and H3.3 in the 2-cell and 8-cell stages, a positive association with H3K27Ac and H3K4me3, and a negative correlation with H3K27me3. Allelic reprogramming analysis of TH2B in embryos from C57BL/6J and DBA/2J crosses revealed differential dynamics between maternal and paternal alleles, with a notable paternal bias at the promoter in 2-cell embryos. Thus, TH2B's enrichment in early embryonic stages and its association with key regulatory regions and histone modifications underscore its importance in ZGA and subsequent developmental processes.

Protein Modifications During Early Embryo Development.

Infertility is a global reproductive health burden. Assisted reproductive technologies (ARTs) have been widely used to help patients become pregnant. Few embryos develop to the blastocyst stage with ARTs, leading to relatively low live birth rates. Protein modifications play crucial roles in nearly every aspect of cell biology, including reproductive processes. The aim of this study was to explore the characteristics of protein modifications during embryonic development. Proteomic data from humans and mice were acquired from the integrated proteome resources (iProX) of ProteomeXchange (PXD024267) and a tandem mass tag (TMT)-mass spectrometry dataset. Gene ontology (GO) analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis were applied for functional annotation. Protein-protein interactions (PPIs) of the modification-related genes were revealed by the STRING database. Modified proteins during mouse embryogenesis were visualized through heatmaps of hierarchically clustering using k-means. We identified modification-related proteins in human embryo development and characterized them through heatmaps, GO analysis, KEGG analysis, and PPI network analysis. We found that the 4-cell stage to the 8-cell stage might be the demarcation period for modification-related protein expression patterns during embryo development. Using quantitative mass spectrometry, we elucidated the methylation, acetylation, and ubiquitination events that occur during mouse embryogenesis to validate our findings in human embryonic development to some extent. The results of our study suggest that the posttranslational modifications (PTMs) of human preimplantation embryos might exhibit the same trends as those in mice to exert synergistic and fine-tuned regulatory effects during embryonic development.

Long-range transcription factor binding sites clustered regions may mediate transcriptional regulation through phase-separation interactions in early human embryo

In mammals, during the post-fertilization pre-implantation phase, the expression of cell type-specific genes is crucial for normal embryonic development, which is regulated by cis-regulatory elements (CREs). TFs control gene expression by interacting with CREs. Research shows that transcription factor binding sites (TFBSs) reflect the general characteristics of the regulatory genome. Here, we identified TFBSs from chromatin accessibility data in five stages of early human embryonic development, and quantified transcription factor binding sites-clustered regions (TFCRs) and their complexity (TC). Assigning TC values to TFCRs has made it possible to assess the functionality of these regulatory elements in a more quantitative way. Our findings reveal a robust correlation between TFCR complexity and gene expression starting from the 8Cell stage, which is when the zygotic genome is activated in humans. Furthermore, we have defined long-range TFCRs (LR-TFCRs) and conjecture that LR-TFCRs may regulate gene expression through phase-separation mechanisms during the early stages of human embryonic development.

Transcriptome analysis of the effects of high temperature on zygotic genome activation in porcine embryos

Damage to the development of porcine gametes and embryos caused by high temperatures (HT) is one of the main reasons for the decline in the economic benefits of the livestock industry. Zygotic genome activation (ZGA) marks the beginning of gene expression programs in mammalian pre-implantation embryos. In pigs, ZGA occurs at the 4-cell (4 C) stage, indicating that correct gene expression at this stage plays an important regulatory role in embryonic development. However, the effect of the HT environment on early porcine embryonic development and the RNA expression profile of ZGA remain unclear. In this study, we compared the RNA transcription patterns of porcine 4 C embryos under normal and HT conditions using RNA-seq and identified 326 differentially expressed genes (DEGs). These changes were mainly related to DNA polymerase activity, DNA replication, and nucleotidyltransferase activity. In addition, entries for reverse transcription and endonuclease activity were enriched, indicating that ZGA interfered under HT conditions. Further comparison of the experimental results with the porcine ZGA gene revealed 39 ZGA genes among the DEGs. KEGG and GSEA analysis showed that the oxidative phosphorylation pathway was significantly enriched and signaling pathways related to energy metabolism were significantly downregulated. We also found that NDUFA6 and CDKN1A were located at the center of the protein-protein interaction network diagram of the DEGs. In summary, HT conditions affect mitochondrial function and oxidative phosphorylation levels, and lead to changes in the expression pattern of ZGA in early porcine embryos, with its hub genes NDUFA6 and CDKN1A.

VPS34 Governs Oocyte Developmental Competence by Regulating Mito/Autophagy: A Novel Insight into the Significance of RAB7 Activity and Its Subcellular Location.

Asynchronous nuclear and cytoplasmic maturation in human oocytes is believed to cause morphological anomalies after controlled ovarian hyperstimulation. Vacuolar protein sorting 34 (VPS34) is renowned for its pivotal role in regulating autophagy and endocytic trafficking. To investigate its impact on oocyte development, oocyte-specific knockout mice (ZcKO) are generated, and these mice are completely found infertile, with embryonic development halted at 2- to 4-cell stage. This infertility is related with a disruption on autophagic/mitophagic flux in ZcKO oocytes, leading to subsequent failure of zygotic genome activation (ZGA) in derived 2-cell embryos. The findings further elucidated the regulation of VPS34 on the activity and subcellular translocation of RAS-related GTP-binding protein 7 (RAB7), which is critical not only for the maturation of late endosomes and lysosomes, but also for initiating mitophagy via retrograde trafficking. VPS34 binds directly with RAB7 and facilitates its activity conversion through TBC1 domain family member 5 (TBC1D5). Consistent with the cytoplasmic vacuolation observed in ZcKO oocytes, defects in multiple vesicle trafficking systems are also identified in vacuolated human oocytes. Furthermore, activating VPS34 with corynoxin B (CB) treatment improved oocyte quality in aged mice. Hence, VPS34 activation may represent a novel approach to enhance oocyte quality in human artificial reproduction.

Sex-specific DNA methylation and gene expression changes in mouse placentas after early preimplantation alcohol exposure

During pregnancy, exposure to alcohol represents an environmental insult capable of negatively impacting embryonic development. This influence can stem from disruption of molecular profiles, ultimately leading to manifestation of fetal alcohol spectrum disorder. Despite the central role of the placenta in proper embryonic development and successful pregnancy, studies on the placenta in a prenatal alcohol exposure and fetal alcohol spectrum disorder context are markedly lacking. Here, we employed a well-established model for preimplantation alcohol exposure, specifically targeting embryonic day 2.5, corresponding to the 8-cell stage. The exposure was administered to pregnant C57BL/6 female mice through subcutaneous injection, involving two doses of either 2.5 g/kg 50 % ethanol or an equivalent volume of saline at 2-hour intervals. Morphology, DNA methylation and gene expression patterns were assessed in male and female late-gestation (E18.5) placentas. While overall placental morphology was not altered, we found a significant decrease in male ethanol-exposed embryo weights. When looking at molecular profiles, we uncovered numerous differentially methylated regions (DMRs; 991 in males; 1309 in females) and differentially expressed genes (DEGs; 1046 in males; 340 in females) in the placentas. Remarkably, only 21 DMRs and 54 DEGs were common to both sexes, which were enriched for genes involved in growth factor response pathways. Preimplantation alcohol exposure had a greater impact on imprinted genes expression in male placentas (imprinted DEGs: 18 in males; 1 in females). Finally, by using machine learning model (L1 regularization), we were able to precisely discriminate control and ethanol-exposed placentas based on their specific DNA methylation patterns. This is the first study demonstrating that preimplantation alcohol exposure alters the DNA methylation and transcriptomic profiles of late-gestation placentas in a sex-specific manner. Our findings highlight that the DNA methylation profiles of the placenta could serve as a potent predictive molecular signature for early preimplantation alcohol exposure.

MUM, a maternal unknown message, inhibits early establishment of the medio-lateral axis in the embryo of the kelp Saccharina latissima.

Brown algae are multicellular photosynthetic organisms that have evolved independently of plants and other algae. Here, we have studied the determinism of body axis formation in the kelp Saccharina latissima. After microdissection of the embryo, we show that the stalk, an empty cell that retains the embryo on the maternal tissue, represses longitudinal cell divisions in the early embryo, thereby reinforcing the establishment of the initial apico-basal axis. In addition, it promotes cell growth and controls cell shape and arrangement in the flat oblong embryo composed of cells aligned in rows and columns. Although the stalk persists for several weeks until the embryo reaches at least 500 cells, proper embryogenesis requires connection to maternal tissue only during the first 4 days after fertilisation, i.e. before the embryo reaches the 8-cell stage. Transplantation experiments indicate that the maternal signal is not diffused in seawater, but requires contact between the embryo and the maternal tissue. This first global quantitative study of brown algal embryogenesis highlights the role of MUM, an unknown maternal message, in the control of growth axes and tissue patterning in kelp embryos.

Sperm-carried IGF2: towards the discovery of a spark contributing to embryo growth and development.

Spermatozoa have been shown to carry key RNAs which, according to animal evidence, seem to play a role in early embryo development. In this context, a potential key growth regulator is insulin-like growth factor 2 (IGF2), a highly conserved paternally expressed imprinted gene involved in cell growth and proliferation which, recent observations indicate, is expressed in human spermatozoa. We herein hypothesized that sperm IGF2 gene expression and transmission at fertilization is required to support early embryo development. To test this hypothesis, we analyzed sperm IGF2 mRNA levels in the same semen aliquot used for homologous assisted reproductive technique (ART) in infertile couples and correlated these levels with embryo morphokinetics. To find a mechanistic explanation for the observed results, the transcriptomes of blastocysts obtained after injection of Igf2 mRNA in mouse parthenotes were analyzed. Sperm IGF2 mRNA negatively correlated with time of 2-cell stage (t2), t3, t4, t5, and time of expanded blastocyst (tEB), independently of maternal age, body mass index, anti-Müllerian hormone levels, and oocyte quality. An IGF2 mRNA index >4.9 predicted the ability of the embryos to reach the blastocyst stage on Day 5, with a sensitivity of 100% and a specificity of 71.6% (AUC 0.845; P < 0.001). In the animal study, transcriptome analysis demonstrated that 65 and 36 genes were, respectively, up- and down-regulated in the experimental group compared to the control group. These genes belong to pathways that regulate early embryo development, thus supporting the findings found in humans. This study has the potential to challenge the longstanding tenet that spermatozoa are simply vehicles carrying paternal DNA. Instead, it suggests that IGF2 mRNA in healthy spermatozoa provides critical support for early embryo development. Pre-ART sperm-carried IGF2 mRNA levels may be used as a marker to predict the chances of obtaining blastocysts to be transferred for infertile couples undergoing ART.

MAT2A is essential for zygotic genome activation by maintaining of histone methylation in porcine embryos

Methionine adenosyltransferase 2A (MAT2A) is an essential enzyme in the methionine cycle that generates S-adenosylmethionine (SAM) by reacting with methionine and ATP. SAM acts as a methyl donors for histone and DNA methylation, which plays key roles in zygotic genome activation (ZGA). However, the effects of MAT2A on porcine ZGA remain unclear. To investigate the function of MAT2A and its underlying mechanism in porcine ZGA, MAT2A was knocked down by double-stranded RNA injection at the 1-cell stage. MAT2A is highly expressed at every stage of porcine embryo development. The percentages of four-cell-stage embryos and blastocysts were lower in the MAT2A-knockdown (KD) group than in the control group. Notably, depletion of MAT2A decreased the levels of H3K4me2, H3K9me2/3, and H3K27me3 at the four-cell stage, whereas MAT2A KD reduced the transcriptional activity of ZGA genes. MAT2A KD decreased embryonic ectoderm development (EED) and enhancer of zeste homolog 2 (EZH2) expression. Exogenous SAM supplementation rescued histone methylation levels and developmental arrest induced by MAT2A KD. Additionally, MAT2A KD significantly increased DNA damage and apoptosis. In conclusion, MAT2A is involved in regulating transcriptional activity and is essential for regulating histone methylation during porcine ZGA.