Codon usage and 3â² UTR length determine maternal mRNA stability in zebrafish
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ABSTRACT: The control of mRNA stability plays a central role in regulating gene expression. In metazoans, the earliest stages of development are driven by maternally supplied mRNAs. The degradation of these maternal mRNAs is critical for promoting the maternal-to-zygotic transition of developmental programs, although the underlying mechanisms are poorly understood in vertebrates. Here, we characterized maternal mRNA degradation pathways in zebrafish using a transcriptome analysis and systematic reporter assays. Our data demonstrate that ORFs enriched with uncommon codons promote deadenylation by the CCR4-NOT complex in a translation-dependent manner. This codon-mediated mRNA decay is conditional on the context of the 3â² UTR, with long 3â² UTRs conferring resistance to deadenylation. These results indicate that the combined effect of codon usage and 3â² UTR length determines the stability of maternal mRNAs in zebrafish embryos. Our study thus highlights the codon-mediated mRNA decay as a conserved regulatory mechanism in eukaryotes. zebrafish embryonic mRNA profile at 2 different stages (2 hpf and 6 hpf) in wildtype and 3 additional conditions (miR-430 inhibition, RNApol II inhibition and CNOT7 inhibition) at 6 hpf. All experiments are performed as triplicates
Project description:The control of mRNA stability plays a central role in regulating gene expression. In metazoans, the earliest stages of development are driven by maternally supplied mRNAs. The degradation of these maternal mRNAs is critical for promoting the maternal-to-zygotic transition of developmental programs, although the underlying mechanisms are poorly understood in vertebrates. Here, we characterized maternal mRNA degradation pathways in zebrafish using a transcriptome analysis and systematic reporter assays. Our data demonstrate that ORFs enriched with uncommon codons promote deadenylation by the CCR4-NOT complex in a translation-dependent manner. This codon-mediated mRNA decay is conditional on the context of the 3′ UTR, with long 3′ UTRs conferring resistance to deadenylation. These results indicate that the combined effect of codon usage and 3′ UTR length determines the stability of maternal mRNAs in zebrafish embryos. Our study thus highlights the codon-mediated mRNA decay as a conserved regulatory mechanism in eukaryotes.
Project description:Maternal mRNAs are essential for protein synthesis during oogenesis and early embryogenesis. To adapt translation to specific needs during development, maternal mRNAs are translationally repressed by shortening the polyA tails. While mRNA deadenylation is associated with decapping and degradation in somatic cells, maternal mRNAs with short polyA tails are stable. Here we report an essential role for the germline-specific paralog of the mRNA cap-binding factor eIF4E, known as eIF4E1b, in the storage and repression of maternal mRNAs with short polyA tails. eIF4E1b binds to the mRNA cap and is targeted to ribonucleoprotein complexes through its direct interaction with eIF4ENIF1/4E-T. In early embryos, eIF4E1b binds to a specific set of translationally repressed mRNAs with short or no polyA tails, such as histone mRNAs, which are translated later on during embryogenesis. Consistent with an important role in maternal mRNA dormancy, mutation of eIF4E1b in zebrafish impairs female germline development. Understanding the mechanism and function of eIF4E1B provides new insights into fundamental post-transcriptional regulatory principles governing early vertebrate development.
Project description:Sox31 is a member of the zebrafish SoxB1 subfamily, and its expression can be detected both pre- and post-MBT. To distinguish the function of its maternal and zygotic transcripts, a splice blocking morpholino (Sb MO) was designed to interfere with the processing of new, zygotically synthesised mRNAs without interfering with mRNAs of maternal origin. Developmental arrest was observed in Sb MO which could not bypass MBT. Mid-Blastula Transition (MBT) functions as a time window for zygotic genome activation and maternal mRNA degradation. To uncover whether the “zygotic up” and “maternal down” event during MBT is retarded in Sb morphants, we performed microarray experiment at the end of MBT (about 4.3 hours post fertilication/4.3 hpf) to compare mRNAs from Sb morphants and control embryos. In one experiment, three flocks of zebrafish eggs were injected with the Sox19b morpholino immediately after fertilization, while another three control populations were injected with placebo. At 4.3 hpf, these six flocks of embryos were sent for gene expression profiling with six Affymetrix Zebrafish Genome Arrays. In another experiment, we compared two wildtype embryo samples at 4h (post-MBT) against two wildtype samples at 2.5 h (pre-MBT).
Project description:MicroRNAs comprise 1-3% of all vertebrate genes, but their in vivo functions and mechanisms of action remain largely unknown. Zebrafish miR-430 is expressed at the onset of zygotic transcription and regulates morphogenesis during early development. Using a microarray approach and in vivo target validation, we find that miR-430 directly regulates several hundred target mRNAs. Targets are highly enriched for maternal mRNAs that accumulate in the absence of miR-430. We also show that miR-430 accelerates the deadenylation of target mRNAs. These results suggest that miR-430 facilitates the deadenylation and clearance of maternal mRNAs during early embryogenesis. Keywords: Dicer, MZdicer, miR-430, miRNA target, maternal, zygotic
Project description:In zebrafish, ovulated oocytes contain both cortisol deposited from the maternal circulation and maternal mRNA for the glucocorticoid receptor (gr mRNA), which is spread as granular structures throughout the central ooplasm. At the 1-cell stage (0.2 hpf), this transcript is relocated by streamers in the blastodisc area and equally partitioned among blastomeres. At 15 hpf, it is replaced by the zygotic transcript. Morpholino knockdown was applied to block translation (grATG1MO or MO2-nr3c1 and grATG2MO or MO3-nr3c1) of both maternal and zygotic gr transcripts, while a missplicing morpholino (grmismMO or MO4-nr3c1) was used to block post-transcriptionally the zygotic transcript alone. MO2-nr3c1 and MO3-nr3c1 (but not MO4-nr3c1) treatment produced craniofacial and caudal malformations in 1-dpf embryos and 5-dpf larvae, which were also affected by pericardial oedema, persistent yolk sac, reduced subintestinal veins, altered neurogenesis and uninflated swim bladder. Such effects were rescued with trout gr2 mRNA. Pangenomic microarray analysis revealed that 114 and 37 highly expressed transcripts were up- and down-regulated, respectively, by maternal GR protein deficiency in 5-hpf embryos. Similar alterations were found at 10 hpf. These effects were confirmed by real-time PCR of 2 up- (casp8, grp1 and igf2a) and 1 down-regulated transcripts (mcm6) evaluated at 4, 8 and 12 hpf. As the contents of transcripts were modified already at 4 hpf, it seems that the lack of GR affects both ways the molecular machinery for the degradation of maternal mRNAs. These results indicate that the maternal gr transcript participates in the maternal programming of zebrafish development. MO2-nr3c1 morphants were compared with MO2-nr3c1-5m morphants at 5 hpf and 10 hpf. MO2-nr3c1 morphants were compared with wild type (WT) at 5 hpf and 10 hpf. MO2-nr3c1 is a morpholino selected to knockdown translation of gr mRNA. MO2-nr3c1-5m is a specific control morpholino.
Project description:In zebrafish, ovulated oocytes contain both cortisol deposited from the maternal circulation and maternal mRNA for the glucocorticoid receptor (gr mRNA), which is spread as granular structures throughout the central ooplasm. At the 1-cell stage (0.2 hpf), this transcript is relocated by streamers in the blastodisc area and equally partitioned among blastomeres. At 15 hpf, it is replaced by the zygotic transcript. Morpholino knockdown was applied to block translation (grATG1MO or MO2-nr3c1 and grATG2MO or MO3-nr3c1) of both maternal and zygotic gr transcripts, while a missplicing morpholino (grmismMO or MO4-nr3c1) was used to block post-transcriptionally the zygotic transcript alone. MO2-nr3c1 and MO3-nr3c1 (but not MO4-nr3c1) treatment produced craniofacial and caudal malformations in 1-dpf embryos and 5-dpf larvae, which were also affected by pericardial oedema, persistent yolk sac, reduced subintestinal veins, altered neurogenesis and uninflated swim bladder. Such effects were rescued with trout gr2 mRNA. Pangenomic microarray analysis revealed that 114 and 37 highly expressed transcripts were up- and down-regulated, respectively, by maternal GR protein deficiency in 5-hpf embryos. Similar alterations were found at 10 hpf. These effects were confirmed by real-time PCR of 2 up- (casp8, grp1 and igf2a) and 1 down-regulated transcripts (mcm6) evaluated at 4, 8 and 12 hpf. As the contents of transcripts were modified already at 4 hpf, it seems that the lack of GR affects both ways the molecular machinery for the degradation of maternal mRNAs. These results indicate that the maternal gr transcript participates in the maternal programming of zebrafish development.
Project description:MicroRNAs comprise 1-3% of all vertebrate genes, but their in vivo functions and mechanisms of action remain largely unknown. Zebrafish miR-430 is expressed at the onset of zygotic transcription and regulates morphogenesis during early development. Using a microarray approach and in vivo target validation, we find that miR-430 directly regulates several hundred target mRNAs. Targets are highly enriched for maternal mRNAs that accumulate in the absence of miR-430. We also show that miR-430 accelerates the deadenylation of target mRNAs. These results suggest that miR-430 facilitates the deadenylation and clearance of maternal mRNAs during early embryogenesis. Experiment Overall Design: As a first step towards the identification of miR-430 targets, we compared the rate of mRNA degradation in wild type and maternal-zygotic (MZ) dicer mutant embryos, which are deficient in miRNA processing. We found that the rate of degradation of a target mRNA with partial complementarity to miR-430 is significantly reduced in MZdicer mutants. Providing miR-430 duplexes to MZdicer mutants restores the rate of target decay. These results indicate that miR-430 enhances the decay of target mRNAs. Experiment Overall Design: To identify miR-430 in vivo targets, we compared the mRNA expression profile of embryos that were wild-type, MZdicer, or MZdicer rescued with miR-430 (MZdicer+miR-430). This analysis identified ~600 genes that were upregulated in MZdicer, but not in MZdicer+miR-430. Experiment Overall Design: We have also analyzed the expression profile of the genes in the array at three different time points, one maternal stage(16 cell), and two Zygotic stages 5 hours and 9 hours
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:Early embryonic development depends on proper utilization and clearance of maternal transcriptomes. How these processes are spatiotemporally regulated remains unclear. Here we show that nuclear RNA-binding protein Rbm14 and maternal mRNAs co-phase separate into cytoplasmic condensates to facilitate vertebrate blastula-to-gastrula development. In zebrafish, Rbm14 condensates were highly abundant in blastomeres and markedly reduced after prominent activation of zygotic transcription. They concentrated at spindle poles by associating with centrosomal -tubulin puncta and displayed mainly asymmetric divisions with a global symmetry across embryonic midline in 8-cell and 16-cell embryos. Their formation was dose-dependently stimulated by m6A, but repressed by m5C modification of the maternal mRNA. Furthermore, deadenylase Parn co-phase separated with these condensates, and this was required for deadenylation of the mRNAs in early blastomeres. Depletion of Rbm14 impaired embryonic cell differentiations and full activations of the zygotic genome in both zebrafish and mouse and resulted in developmental arrest at the blastula stage. Our results suggest that cytoplasmic Rbm14 condensate formation regulates early embryogenesis by facilitating deadenylation, protection, and mitotic allocation of m6A-modified maternal mRNAs, and by releasing the poly(A)-less transcripts upon regulated disassembly to allow their re-polyadenylation and translation or clearance.