Global characterization of the oocyte-to-embryo transition in C. elegans uncovers a novel mRNA turnover mechanism
Ontology highlight
ABSTRACT: The oocyte-to-embryo transition (OET) is thought to be mainly driven by post-transcriptional gene regulation. However, expression of both RNAs and proteins during the OET has not been comprehensively assayed. Furthermore, specific molecular mechanisms that regulate gene expression during OET are largely unknown. Here, we quantify and analyze, transcriptome-wide, expression of mRNAs, small RNAs and thousands of proteins in C. elegans oocytes, 1-cell, and 2-cell embryos. This represents a first comprehensive gene expression atlas during the OET in animals. We discovered a first wave of degradation in which thousands of mRNAs are turned over shortly after fertilization. Sequence analysis revealed a statistically highly significant presence of a novel polyC motif in the 3' untranslated regions (3' UTRs) of most of these degraded mRNAs. Transgenic reporter assays showed that this polyC motif is indeed required and sufficient for mRNA degradation after fertilization. We show that orthologs of human poly-C binding-protein specifically bind this motif. Together, our data suggest a mechanism in which the polyC motif and binding partners direct degradation of maternal mRNAs. Our data also indicate that endogenous siRNAs but not miRNAs promote mRNA clearance during the OET.
Project description:The oocyte-to-embryo transition (OET) is thought to be mainly driven by post-transcriptional gene regulation. However, expression of both RNAs and proteins during the OET has not been comprehensively assayed. Furthermore, specific molecular mechanisms that regulate gene expression during OET are largely unknown. Here, we quantify and analyze, transcriptome-wide, expression of mRNAs, small RNAs and thousands of proteins in C. elegans oocytes, 1-cell, and 2-cell embryos. This represents a first comprehensive gene expression atlas during the OET in animals. We discovered a first wave of degradation in which thousands of mRNAs are turned over shortly after fertilization. Sequence analysis revealed a statistically highly significant presence of a novel polyC motif in the 3' untranslated regions (3' UTRs) of most of these degraded mRNAs. Transgenic reporter assays showed that this polyC motif is indeed required and sufficient for mRNA degradation after fertilization. We show that orthologs of human poly-C binding-protein specifically bind this motif. Together, our data suggest a mechanism in which the polyC motif and binding partners direct degradation of maternal mRNAs. Our data also indicate that endogenous siRNAs but not miRNAs promote mRNA clearance during the OET. To study the OET in C.elegans we isolated large quantities of oocytes, 1-cell embryos, 2-cell embryos and sperm. We sequenced then sequenced polyA RNA.
Project description:The post-transcriptional fate of messenger RNAs (mRNAs) is largely dictated by their 3' untranslated regions (3'UTRs), which are defined by cleavage and polyadenylation (CPA) of pre-mRNAs. We used poly(A)-position profiling by sequencing (3P-Seq) to map poly(A) sites at eight developmental stages and tissues in the zebrafish. Analysis of over 60 million 3P-Seq reads substantially increased and improved existing 3'UTR annotations, resulting in confidently identified 3'UTRs for more than 78.79% of the annotated protein-coding genes in zebrafish. Most zebrafish genes undergo alternative CPA with more than a thousand genes using different dominant 3'UTRs at different stages. 3'UTRs tend to be shortest in the ovaries and longest in the brain. Isoforms with some of the shortest 3'UTRs are highly expressed in the ovary yet absent in the maternally contributed RNAs of the embryo, perhaps because their 3'UTRs are too short to accommodate a uridine-rich motif required for stability of the maternal mRNA. At two hours post-fertilization, thousands of unique poly(A) sites appear at locations lacking a typical polyadenylation signal, which suggests a wave of widespread cytoplasmic polyadenylation of mRNA degradation intermediates. Our insights into the identities, formation, and evolution of zebrafish 3'UTRs provide a resource for studying gene regulation during vertebrate development. 3P-Seq was used to map the 3' ends of protein-coding genes in the zebrafish genome
Project description:The oocyte-to-embryo transition (OET) occurs in the absence of new transcription and relies on post-transcriptional gene regulation, including translational control by mRNA poly(A) tail regulation, where cytoplasmic polyadenylation activates translation and deadenylation leads to translational repression and decay. However, how the transcriptome-wide landscape of mRNA poly(A) tails shapes translation across the OET in mammals remains unknown. Here, we performed long-read RNA sequencing to uncover poly(A) tail lengths and mRNA abundance transcriptome-wide in mice across five stages of development from oocyte to embryo. Integrating these data with recently published ribosome profiling data, we demonstrate that poly(A) tail length is coupled to translational efficiency across the entire OET. We uncover an extended wave of global deadenylation during fertilization, which sets up a switch in translation control between the oocyte and embryo. In the oocyte, short-tailed maternal mRNAs that resist deadenylation in the oocyte are translationally activated, whereas large groups of mRNAs deadenylated without decay in the oocyte are later readenylated to drive translation activation in the early embryo. Our findings provide an important resource and insight into the mechanisms by which cytoplasmic polyadenylation and deadenylation dynamically shape poly(A) tail length in a stage-specific manner to orchestrate development from oocyte to embryo in mammals.
Project description:The post-transcriptional fate of messenger RNAs (mRNAs) is largely dictated by their 3' untranslated regions (3'UTRs), which are defined by cleavage and polyadenylation (CPA) of pre-mRNAs. We used poly(A)-position profiling by sequencing (3P-Seq) to map poly(A) sites at eight developmental stages and tissues in the zebrafish. Analysis of over 60 million 3P-Seq reads substantially increased and improved existing 3'UTR annotations, resulting in confidently identified 3'UTRs for more than 78.79% of the annotated protein-coding genes in zebrafish. Most zebrafish genes undergo alternative CPA with more than a thousand genes using different dominant 3'UTRs at different stages. 3'UTRs tend to be shortest in the ovaries and longest in the brain. Isoforms with some of the shortest 3'UTRs are highly expressed in the ovary yet absent in the maternally contributed RNAs of the embryo, perhaps because their 3'UTRs are too short to accommodate a uridine-rich motif required for stability of the maternal mRNA. At two hours post-fertilization, thousands of unique poly(A) sites appear at locations lacking a typical polyadenylation signal, which suggests a wave of widespread cytoplasmic polyadenylation of mRNA degradation intermediates. Our insights into the identities, formation, and evolution of zebrafish 3'UTRs provide a resource for studying gene regulation during vertebrate development.
Project description:The nuanced mechanisms driving primordial germ cells (PGC) specification remain incompletely understood since genome-wide transcriptional regulation in developing PGCs has previously only been defined indirectly. Here, using SLAMseq analysis, we determined genome-wide transcription rates during the differentiation of embryonic stem cells (ESCs) to form epiblast-like (EpiLC) cells and ultimately PGC-like cells (PGCLCs). This revealed thousands of genes undergoing bursts of transcriptional induction and rapid shut-off not detectable by RNAseq analysis. Our SLAMseq datasets also allowed us to infer RNA turnover rates, which revealed thousands of mRNAs stabilized and destabilized during PGCLC specification. mRNAs tend to be unstable in ESCs and then are progressively stabilized as they differentiate. For some classes of genes, mRNA turnover regulation collaborates with transcriptional regulation, but these processes opposed each other in a surprisingly high frequency of genes. To test whether regulated mRNA turnover has a physiological role in PGC development, we examined 3 genes that we found were regulated by RNA turnover: Sox2, Klf2, and Ccne1. Circumvention of their regulated RNA turnover severely impaired the ESC-to-EpiLC and EpiLC-to-PGCLC transitions. Our study demonstrates the functional importance of regulated RNA stability in germline development and provides a roadmap of transcriptional and post-transcriptional regulation during germline specification.
Project description:In sexually reproducing animals, the oocyte contributes a large supply of RNAs that are essential to launch development upon fertilization. The mechanisms that regulate the composition of the maternal RNA contribution during oogenesis are unclear. Here, we show that a subset of RNAs expressed during the early stages of oogenesis is subjected to regulated degradation during oocyte specification. Failure to remove these RNAs results in oocyte dysfunction and death. We identify the RNA-degrading Super Killer complex and No-Go Decay factor Pelota as key regulators of oogenesis via targeted degradation of specific RNAs expressed in undifferentiated germ cells. These regulators target RNAs enriched for cytidine sequences that are bound by the polypyrimidine tract binding protein Half pint. Thus, RNA degradation helps orchestrate a germ cell-to-maternal transition by sculpting RNAs that become part of the maternal contribution to the zygote.
Project description:Spatial organization of the transcriptome has emerged as a powerful means for regulating the post-transcriptional fate of RNA in eukaryotes; however, whether prokaryotes use RNA spatial organization as a mechanism for post-transcriptional regulation remains unclear. Here we used super-resolution microscopy to image the E. coli transcriptome and observed a genome-wide spatial organization of RNA: mRNAs encoding inner-membrane proteins are enriched at the membrane, whereas mRNAs encoding outer-membrane, cytoplasmic and periplasmic proteins are distributed throughout the cytoplasm. Membrane enrichment is caused by co-translational insertion of signal peptides recognized by the signal-recognition particle. Our time-resolved RNA-sequencing and live-cell super-resolution imaging experiments revealed a physiological consequence of this spatial organization and the underlying mechanism: membrane localization enhances degradation rates of inner-membrane-protein mRNAs by placing them in proximity to membrane-bound RNA degradation enzymes. Together, these results demonstrate that the bacterial transcriptome is spatially organized and that this organization shapes the posttranscriptional Spatial organization of the transcriptome has emerged as a powerful means for regulating the post-transcriptional fate of RNA in eukaryotes; however, whether prokaryotes use RNA spatial organization as a mechanism for post-transcriptional regulation remains unclear. Here we used super-resolution microscopy to image the E. coli transcriptome and observed a genome-wide spatial organization of RNA: mRNAs encoding inner-membrane proteins are enriched at the membrane, whereas mRNAs encoding outer-membrane, cytoplasmic and periplasmic proteins are distributed throughout the cytoplasm. Membrane enrichment is caused by co-translational insertion of signal peptides recognized by the signal-recognition particle. Our time-resolved RNA-sequencing and live-cell super-resolution imaging experiments revealed a physiological consequence of this spatial organization and the underlying mechanism: membrane localization enhances degradation rates of inner-membrane-protein mRNAs by placing them in proximity to membrane-bound RNA degradation enzymes. Together, these results demonstrate that the bacterial transcriptome is spatially organized and that this organization shapes the post-transcriptional dynamics of mRNAs.
Project description:Maternal-to-zygotic transition (MZT) is a conserved and fundamental process during which the maternal environment of oocyte transits to the zygotic genome driven expression program, and terminally differentiated oocyte and sperm are reprogrammed to totipotency. It is initiated by maternal mRNAs and proteins during the period of zygotic genome quiescence after fertilization, followed by a gradual switch to zygotic genome activation and accompanied by clearance of maternal RNAs and proteins. A key question for embryonic development is how MZT process is regulated. Here we used a low-input proteomic analysis to measure the proteomic dynamics during early development of mouse maternal-to-zygotic transition.
Project description:In response to foreign and endogenous double-stranded RNA (dsRNA), protein kinase R (PKR) and ribonuclease L (RNase L) reprogram translation in mammalian cells. PKR inhibits translation initiation through eIF2 phosphorylation, which triggers stress granule (SG) formation and promotes translation of stress responsive mRNAs. The mechanisms of RNase L-driven translation repression, its contribution to SG assembly, and its regulation of dsRNA stress-induced mRNAs are unknown. We demonstrate that RNase L drives translational shut-off in response to dsRNA by promoting widespread turnover of mRNAs. This alters stress granule assembly and reprograms translation by only allowing for the translation of mRNAs resistant to RNase L degradation, including numerous antiviral mRNAs such as IFN- . Individual cells differentially activate dsRNA responses revealing variation that can affect cellular outcomes. This identifies bulk mRNA degradation and the resistance of antiviral mRNAs as the mechanism by which RNaseL reprograms translation in response to dsRNA.
Project description:In the Caenorhabditis elegans germline, thousands of mRNAs are concomitantly expressed with antisense 22G-RNAs, which are loaded into the Argonaute CSR-1. Despite their essential functions for animal fertility and embryonic development, how CSR-1 22G-RNAs are produced remains unknown. Here, we show that CSR-1 slicer activity is primarily involved in triggering the synthesis of small RNAs on the coding sequences of germline mRNAs and post-transcriptionally regulates a fraction of targets. CSR-1-cleaved mRNAs prime the RNA-dependent RNA polymerase, EGO-1, to synthesize 22G-RNAs in phase with ribosome translation in the cytoplasm, in contrast to other 22G-RNAs mostly synthesized in germ granules. Moreover, codon optimality and efficient translation antagonize CSR-1 slicing and 22G-RNAs biogenesis. We propose that codon usage differences encoded into mRNA sequences might be a conserved strategy in eukaryotes to regulate small RNA biogenesis and Argonaute targeting