Project description:Embryogenesis entails dramatic shifts in mRNA translation and turnover to account for gene expression differences during proliferation and cellular differentiation. Codon identity modulates mRNA stability during early vertebrate embryogenesis, but how the composition of tRNA pools adapts to the embryo s translational demand is unknown. By quantitatively profiling the tRNA repertoires of zebrafish embryos during the maternal-to-zygotic transition, here we find that maternal and zygotic tRNA pools are distinct. We show that translational activation during embryogenesis and tRNA gene derepression are temporally coordinated by TORC1 activity, which increases at gastrulation and inactivates the RNA polymerase III repressor Maf1a/b in vivo. Reshaping of tRNA pools results in differential tRNA anticodon supply, but these changes do not alter decoding rates in zebrafish embryos. Instead, our data indicate that tRNA repertoires reflect the inherent codon bias of the zebrafish mRNA transcriptome, and tRNA levels are boosted at gastrulation to ensure efficient translation as embryos enter differentiation.
Project description:To study the function of zebrafish nuclear pores during early embryogenesis, we generated maternal zygotic double mutant of nup85;nup133 (MZnup85;nup133) using CRISPR/Cas9 and report the transcriptome-wide changes in comparison to wild-type (WT) embryos. Our analysis reveals a dramatic delay of maternal mRNA degradation and zygotic genome activation in MZnup85;nup133 embryos during maternal-to-zygotic transition.
Project description:To study the function of zebrafish Ybx1 during early embryogenesis, we generated maternal ybx1 (Mybx1) mutant using CRISPR/Cas9 and report the transcriptome-wide changes in comparison to wild-type (WT) embryos. Our analysis reveals a dramatic loss of maternal mRNA decay and zygotic genome activation in Mybx1 embryos during maternal-to-zygotic transition.
Project description:The position of nucleosomes influences DNA accessibility to DNA-binding proteins. Genome-wide nucleosome profiles often report the observation of a canonical nucleosome organization at gene promoters where arrays of well-positioned nucleosomes emanate from nucleosome-depleted regions. It is unclear how this canonical promoter nucleosome organization forms and how it is related to transcription activation and the establishment of histone marks during development. Here we report the genome-wide organization of nucleosomes during zebrafish embryogenesis and show that well-positioned nucleosome arrays appear in thousands of promoters during the activation of the zygotic genome. The formation of canonical promoter nucleosome organization cannot be explained by DNA sequence preference, and is independent of transcription and the presence of RNA polymerase II, but strongly correlates with the presence of Histone H3 Lysine 4 trimethylation (H3K4me3). Our study further suggests that promoter nucleosome structure primes genes to future transcription activation. Together, this study reveals that genome activation but not transcription underlies the organization of nucleosome arrays during early embryogenesis. MNase-seq to generate nucleosome organization in two stages of zebrafish development; two biological replicates for each stage. 7 ChIP-seq experiments in three stages.
Project description:Background: Early embryonic developmental programs are guided by the coordinated interplay between maternally inherited and zygotically manufactured RNAs and proteins. Although these processes happen concomitantly and affecting gene function during this period is bound to affect both pools of mRNAs, it has been challenging to study their expression dynamics separately. Results: By employing Slam-seq, a nascent mRNA labeling transcriptomic approach, in a developmental time series we observe that over half of the early zebrafish embryo transcriptome consists of maternal-zygotic genes, emphasizing their pivotal role in early embryogenesis. We provide an hourly resolution of de novo transcriptional waves and follow nascent mRNA trajectories, finding that most de novo transcriptional events are stable throughout this period. Additionally, by blocking microRNA430 function, a key post-transcriptional regulator during zebrafish embryogenesis, we directly show that it destabilizes hundreds of de novo transcribed mRNAs from pure zygotic as well as maternal-zygotic genes. This unveils a novel miR-430 function during embryogenesis, fine-tuning zygotic gene expression, which highlights that Slam-seq can be used to disentangle transcriptional and post-transcriptional regulation of mRNA levels. Conclusion: Such valuable insights into zebrafish early embryo transcriptome dynamics emphasize the significance of post-transcriptional regulators in zygotic genome activation. These findings pave the way for future investigations into the coordinated interplay between transcriptional and post-transcriptional landscapes required for the establishment of animal cell identities and functions.
Project description:Background: Early embryonic developmental programs are guided by the coordinated interplay between maternally inherited and zygotically manufactured RNAs and proteins. Although these processes happen concomitantly and affecting gene function during this period is bound to affect both pools of mRNAs, it has been challenging to study their expression dynamics separately. Results: By employing Slam-seq, a nascent mRNA labeling transcriptomic approach, in a developmental time series we observe that over half of the early zebrafish embryo transcriptome consists of maternal-zygotic genes, emphasizing their pivotal role in early embryogenesis. We provide an hourly resolution of de novo transcriptional waves and follow nascent mRNA trajectories, finding that most de novo transcriptional events are stable throughout this period. Additionally, by blocking microRNA430 function, a key post-transcriptional regulator during zebrafish embryogenesis, we directly show that it destabilizes hundreds of de novo transcribed mRNAs from pure zygotic as well as maternal-zygotic genes. This unveils a novel miR-430 function during embryogenesis, fine-tuning zygotic gene expression, which highlights that Slam-seq can be used to disentangle transcriptional and post-transcriptional regulation of mRNA levels. Conclusion: Such valuable insights into zebrafish early embryo transcriptome dynamics emphasize the significance of post-transcriptional regulators in zygotic genome activation. These findings pave the way for future investigations into the coordinated interplay between transcriptional and post-transcriptional landscapes required for the establishment of animal cell identities and functions.
Project description:Background: Early embryonic developmental programs are guided by the coordinated interplay between maternally inherited and zygotically manufactured RNAs and proteins. Although these processes happen concomitantly and affecting gene function during this period is bound to affect both pools of mRNAs, it has been challenging to study their expression dynamics separately. Results: By employing Slam-seq, a nascent mRNA labeling transcriptomic approach, in a developmental time series we observe that over half of the early zebrafish embryo transcriptome consists of maternal-zygotic genes, emphasizing their pivotal role in early embryogenesis. We provide an hourly resolution of de novo transcriptional waves and follow nascent mRNA trajectories, finding that most de novo transcriptional events are stable throughout this period. Additionally, by blocking microRNA430 function, a key post-transcriptional regulator during zebrafish embryogenesis, we directly show that it destabilizes hundreds of de novo transcribed mRNAs from pure zygotic as well as maternal-zygotic genes. This unveils a novel miR-430 function during embryogenesis, fine-tuning zygotic gene expression, which highlights that Slam-seq can be used to disentangle transcriptional and post-transcriptional regulation of mRNA levels. Conclusion: Such valuable insights into zebrafish early embryo transcriptome dynamics emphasize the significance of post-transcriptional regulators in zygotic genome activation. These findings pave the way for future investigations into the coordinated interplay between transcriptional and post-transcriptional landscapes required for the establishment of animal cell identities and functions.
Project description:In many organisms, early embryonic development is driven by maternally provided transcription factors until the controlled onset of transcription during zygotic genome activation (ZGA). The regulation of chromatin accessibility and its relationship to gene activity during this transition remains poorly understood. Here, we generated chromatin accessibility maps for the early stages of zebrafish development spanning genome activation and the onset of lineage specification. We find that during this period, chromatin accessibility increases at regulatory elements. This is independent of RNA pol II-mediated transcription, with the exception of the miR-430 locus. Instead, accessibility often precedes the transcription of associated genes. Loss of the maternal transcription factors pou5f3, sox19b, and nanog, which are known to be required for zebrafish ZGA, results in decreased accessibility at regulatory elements. Finally, we show that accessibility of regulatory regions, especially when established by Pou5f3, Sox19b and Nanog, is predictive for future transcription. Together, our results suggest that maternally provided transcription factors prime genes for activity during zygotic genome activation.
Project description:Cys2-His2 Zinc finger genes (ZNFs) form the largest family of transcription factors in metazoans. Zebrafish posess a subfamily characterized by the presence of a domain dubbed Fish N-terminal Zinc finger associated (FiNZ). FiNZ-ZNFs are expressed at the onset of zygotic genome activation in zebrafishh, and blocking FiNZ-ZNF translation using morpholinos during early zebrafish embryogenesis results in a broad de-repression of young, transcriptionally active TEs.
Project description:During early embryogenesis, embryos undergo a massive degradation of maternally inherited mRNAs and produce new zygotic transcripts. This maternal-to-zygotic transition requires a tight interplay of mRNA transcription and degradation, but distinguishing their unique contributions remains a challenge. Here, we dissect gene regulation during the zebrafish maternal-to-zygotic transition by combining single-cell RNA-sequencing with RNA metabolic labeling and nucleotide conversion within zebrafish embryos. We decompose single-cell transcriptomes into their new (zygotic) and old (maternal) mRNA components, and elicit critical information on gene regulation as it unfolds over both time and space. We show that most cell-type restricted expression arises by zygotic transcription, but distinguish a specific role for maternal transcripts in defining germ-cell and enveloping-layer identity, two earliest specified cell identities. We recover the underlying replacement between maternal and zygotic copies of embryonic genes with a relatively constant overall mRNA level, and associate a fast replacement with genes that has a restricted zygotic expression in either cell-type or time. Our study provides a valuable resource to investigate maternal and zygotic transcriptomes and reveals post-transcriptional events that control gene regulation during early embryogenesis.