Total and Nascent Transcriptome of Xenopus laevis Embryos at 5-9 hpf (stage 7-9)
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ABSTRACT: To characterize the nascent transcriptome during zygotic genome activation (ZGA) of Xenopus laevis embryos, we microinjected 5-ethynyl uridine (EU) into 1-cell stage embryos and isolated total RNAs from whole embryos at 5, 6, 7, 8 and 9 hours post-fertilization (hpf) at room temperature, respectively, covering the stages of pre-ZGA to widespread ZGA (stage 7-9). To purify nascent transcripts, total RNAs were biotinylated using disulfide biotin azide via click reaction and biotinylated nascent transcripts were purified using streptavidin beads. Libraries were constructed from using the total RNA ('All'), nascent transcripts ('Bead') and the flowthrough after purification of nascent transcripts ('FL'), respectively. To categorize maternal-zygotic (MZ) genes and zygotic-only (Z) genes, total RNAs from eggs were isolated for constructing libraries. All libraries were sequenced on illumina NextSeq 500.
Project description:To characterize the spatial patterns of zygtoic transcription during zygotic genome activation (ZGA) of Xenopus laevis embryos, we microinjected 5-ethynyl uridine (EU) into 1-cell stage embryos and isolated total RNAs from whole embryos at 5, 6, 7, 8 and 9 hours post-fertilization (hpf) at room temperature, respectively, covering the stages of pre-ZGA to widespread ZGA (stage 7-9). The animal pole (AP, ~ 1/3 at the top region of embryo) and the vegetal pole (VP,~ 1/3 at the bottom region of embryo) regions were dissected and used for total RNA isolation. To purify nascent transcripts, total RNAs were biotinylated using disulfide biotin azide via click reaction and biotinylated nascent transcripts were purified using streptavidin beads. Libraries were constructed from using the nascent transcripts. All libraries were sequenced on illumina NextSeq 500.
Project description:To characterize the effect of cell cyle elongation on nascent transcription during zygotic genome activation (ZGA) of Xenopus laevis embryos, we microinjected 5-ethynyl uridine (EU) into 1-cell stage embryos and treated the embryos with 0.2 mg/ml of cycloheximide (CHX) to arrest them in interphase from 5 hpf to 7.5 hpf. Control and CHX-arrested embryos were collected for isolating total RNAs, followed by biotinylation using disulfide biotin azide via click reaction and purification of nascent transcripts using streptavidin beads. Libraries were constructed and sequenced on illumina NextSeq 500.
Project description:To validate that EU-RNA imaging provides a direct readout of wide-spread zygotic transcription, we sought to identify the nascent transcriptome using RNA-seq. We micoinjected 5-ethynyl uridine (EU) into 1-cell Xenopus embryos, isolated total RNA from embryos at mid-blastula transition (MBT), biotinylated EU-RNA and purified it to generate cDNA libraries for sequencing. Total RNA from normal embyros were used as control. We found over 25,000 nascent genes in this EU-RNA dataset at mid-ZGA. The nascent transcriptome dataset captures nearly 90% of the transcripts present in the whole-embryo dataset and with similar or better read-depth, indicating that our EU-RNA imaging is truly representative of wide-spread zygotic transcription. Furthermore, of the known zygotic genes that are most highly induced at MBT, we detected all of them and at much higher levels than in the whole-embryo dataset. These results show that our labeling captures the nascent zygotic transcriptome. We found ~ 4-fold higher sensitivity for nascent transcripts in the EU-RNA dataset compared to the whole embryo dataset, and as excepted we did not detect thousands of maternal-only transcripts in the nascent dataset. Together, these results suggest that EU-labeling provides a visual readout of bona fide nascent zygotic transcripts.
Project description:Zygotic genomic activation (ZGA) is a landmark event in the maternal-to-zygotic transition (MZT), and the regulation of ZGA by maternal factors remains to be elucidated. In this study, the depletion of maternal RNF114 led to 2-cell embryos developmental arrest in mice. RNF114 was proven to play an important role in major ZGA using ethynyl uridine (EU) incorporation and transcriptome analysis. To study the underlying mechanism, we performed protein profiling in mature oocytes and found a potential substrate for RNF114, Chromobox protein CBX5, whose ubiquitination and degradation was regulated by RNF114. Furthermore, the overexpression of CBX5 prevented embryonic development and impeded major ZGA. In summary, our study reveals that maternal RNF114, as a ubiquitin E3 ligase, plays a precise role in mediating the degradation of repressive protein CBX5 during MZT, the misregulation of which may impede the appropriate activation of major ZGA in mouse embryos.
Project description:Understanding mammalian preimplantation development, particularly in humans, at the proteomic level remains limited. Here, we applied our comprehensive solution of ultrasensitive proteomic technology to measure the proteomic profiles of oocytes and early embryos and identified nearly 8,000 proteins in humans and over 6,300 proteins in mice. We observed distinct proteomic dynamics before and around zygotic genome activation (ZGA) between the two species. Integrative analysis with translatomic data revealed extensive divergence between translation activation and protein accumulation. Multi-omic analysis indicated that ZGA transcripts often contribute to protein accumulation in blastocysts. Using mouse embryos, we identified several transcriptional regulators critical for early development, thereby linking ZGA to the first lineage specification. Furthermore, single-embryo proteomics of poor-quality embryos from over 100 patient couples provided insights into preimplantation development failure. Our study may contribute to reshaping the framework of mammalian preimplantation development and opening avenues for addressing human infertility.
Project description:During the maternal-to-zygotic transition (MZT), transcriptionally silent embryos rely on post-transcriptional regulation of maternal mRNAs until zygotic genome activation (ZGA). RNA-binding proteins (RBPs) are important regulators of post-transcriptional RNA processing events, yet their identities and functions during developmental transitions in vertebrates remain largely unexplored. Using mRNA interactome capture, we identified 227 RBPs in zebrafish embryos before and during ZGA, hereby named the zebrafish MZT mRNAbound proteome. This protein constellation consists of many conserved RBPs, with additional embryo- and stage-specific mRNA interactors that likely reflect the dynamics of RNA-protein interactions during MZT. The enrichment of numerous splicing factors like hnRNP proteins before ZGA was surprising, because maternal mRNAs were found to be fully spliced. To address potentially unique roles of RBPs in embryogenesis, we focused on hnRNP A1. iCLIP and subsequent mRNA reporter assays revealed a function for hnRNP A1 in the regulation of poly(A) tail length and translation of maternal mRNAs through sequence-specific association with 3’UTRs before ZGA. Comparison of iCLIP data from two developmental stages revealed that hnRNP A1 dissociates from maternal mRNAs at ZGA and instead regulates the nuclear processing of pri-miR-430 transcripts, which we validated experimentally. The shift from cytoplasmic to nuclear RNA targets was accompanied by a dramatic translocation of hnRNP A1 and other pre-mRNA splicing factors to the nucleus in a transcription-dependent manner. Thus, our study identifies global changes in RNA-protein interactions during vertebrate MZT and shows that hnRNP A1 RNA-binding activities are spatially and temporally coordinated to regulate RNA metabolism during early development.
Project description:A conserved event of the maternal-to-zygotic transition (MZT) in animal embryos is the elimination of a subset of the maternal transcripts that accumulated during oogenesis. In invertebrates and lower vertebrates, a maternally encoded mRNA decay pathway (M-decay) acts before zygotic genome activation (ZGA) while a second pathway, which requires zygotic transcription, subsequently clears additional mRNAs (Z-decay). To date it has not been clear whether a Z-decay pathway is present in mammals. Here, we identify mouse and human maternal transcripts that are degraded after ZGA and show that inhibition of de novo transcription stabilizes these mRNAs in mouse and human embryos. We show that YAP1-TEAD4 transcription factor-mediated transcription is essential for Z-decay in mouse embryos and that TEAD4-triggered zygotic Tut4/7 expression and mRNA 3ʹ-oligouridylation direct Z-decay.
Project description:Upon fertilization, the embryonic genome remains transcriptionally inactive until the mid-blastula transition. Zygotic genome activation (ZGA) of vertebrate embryos has been extensively studied using nucleic acid-based strategies, but proteomics data are still scarce, impeding the full mechanistic understanding of how ZGA is executed during the maternal-to-zygotic transition (MZT). Here, we performed quantitative proteomics to decipher the proteome landscape of zebrafish embryos during the MZT, quantifying nearly 5,000 proteins across four embryonic stages. The stage-specific clustering based on protein expression pattern revealed that helicases (i.e., eif4a2 and ruvbl1) facilitate pluripotency factors (i.e., nanog, pou5f3, ctcf, and hmga1) triggering ZGA in zebrafish, accompanied by the maternal product decay with P-bodies and ubiquitin dependent proteolytic pathway. Dozens of transcription factors show wave-like expression patterns during MZT, implying their diverse functions in triggering the ZGA and modulating differentiation for organ development. The combination of morpholino knockdown and quantitative proteomics demonstrated that maternal Nanog is required for proper embryogenesis by regulating 1) interactions with other pluripotency factors, 2) F-actin band formation, 3) cell cycle checkpoints and 4) maternal product degradation. This study represents the most systematic proteomics survey of developmentally regulated proteins and their expression profiles accompanying MZT in zebrafish, which is a valuable proteome resource for understanding ZGA.
Project description:Since discovery of dimethyl sulfoxide (DMSO), it has been applied to the multidisciplinary studies for basic and clinic research; yet its toxicity versus biocompatibility is poorly understood, leading to our inability to discover etiology behind its paradox. Here, we found that exposure of 2% DMSO to mouse zygotes caused developmental arrest at 2/4-cell embryos, and showed a decreased total acetylation levels. Besides, H3, H4, p53, H3K9, and H3K27 acetylation levels at DMSO-exposed 2-cell embryos are significantly increased. This affected the male pronucleus more than female. Further, RNA-sequence data demonstrates that DMSO alters approximately 16.26% transcripts of 2-cell embryos. Among them, maternal and minor zygotic gene activation (ZGA) transcripts are highly increased, whereas ubiquitin-proteasome system, major ZGA, embryonic gene activation, cell cycle, and ribosomal biogenesis transcripts are significantly down-regulated. These results suggest that DMSO caused developmental arrest by disrupting maternal-to-embryonic transition due to low proteasome activity and epigenetic alternations.
Project description:Early zebrafish embryo development proceeds first from a maternally transcribed and stored mRNAs, and zygotic gene activation (ZGA) is initiated at the mid-blastula transition (MBT; 1000-cell stage), 3.3 h post-fertilization. Very little is known on how the zygotic genome is programmed for transcriptional activation at the MBT. To start addressing this issue, we have mapped by ChIP-chip genome-wide promoter histone methylation (H3K4me3, H3K9me3, H3K27me3, H3K36me3) and RNA Pol II profiles before ZGA (256-cell stage; 2.5 hpf), during ZGA (MBT; 3.5 hpf)) and after ZGA (Post-MBT; 5.3 hpf) . We used a custom 2.1M probe HD promoter array (Nimblegen) for ChIP and input DNA hybridization. Peak detection was done using MA2C with P=10e-4 as cutoff. ChIP-chip experiments were performed from chromatin prepared by sonication after formaldehyde cross-linking, from embryos are the indicated developmental stages and ChIP DNA was hybridized onto the aforementioned Nimbegen promoter arrays.