Project description:The GLD-2 class of poly(A) polymerases regulate the timing of translation of stored transcripts by elongating the poly(A) tails of target mRNAs in the cytoplasm. WISPY is a GLD-2 enzyme that acts in the Drosophila female germline and is required for the completion of the egg-to-embryo transition. Though a handful of WISPY target mRNAs have been identified during both oogenesis and early embryogenesis, we aimed to discover the full range of WISPY targets at each stage. To globally identify these targets, we carried out microarray analysis to look for maternal mRNAs whose poly(A) tails fail to elongate in the absence of WISP function. We examined the polyadenylated portion of the maternal transcriptome in both stage 14 (mature) oocytes and in early embryos that had completed egg activation. Our analysis shows that the poly(A) tails of thousands of maternal mRNAs fail to elongate in wisp-deficient oocytes and embryos. Furthermore, we have identified specific classes of genes that are highly regulated in this manner at each stage. Our study shows that cytoplasmic polyadenylation is a major regulatory mechanism during oocyte maturation and egg activation.
Project description:The GLD-2 class of poly(A) polymerases regulate the timing of translation of stored transcripts by elongating the poly(A) tails of target mRNAs in the cytoplasm. WISPY is a GLD-2 enzyme that acts in the Drosophila female germline and is required for the completion of the egg-to-embryo transition. Though a handful of WISPY target mRNAs have been identified during both oogenesis and early embryogenesis, we aimed to discover the full range of WISPY targets at each stage. To globally identify these targets, we carried out microarray analysis to look for maternal mRNAs whose poly(A) tails fail to elongate in the absence of WISP function. We examined the polyadenylated portion of the maternal transcriptome in both stage 14 (mature) oocytes and in early embryos that had completed egg activation. Our analysis shows that the poly(A) tails of thousands of maternal mRNAs fail to elongate in wisp-deficient oocytes and embryos. Furthermore, we have identified specific classes of genes that are highly regulated in this manner at each stage. Our study shows that cytoplasmic polyadenylation is a major regulatory mechanism during oocyte maturation and egg activation. Four groups of comparisons: WT vs. wisp total RNA from stage 14 oocytes, WT vs. wisp total RNA from fertilized eggs, WT vs. wisp poly(A)+ RNA from stage 14 oocytes, WT vs. wisp poly(A)+ RNA from fertilized eggs. Each comparison consisted of three independent RNA extractions and each experiment was done with dye-swap pairs as two technical replicates.
Project description:During vertebrate embryogenesis, hematopoietic stem and progenitor cell (HSPC) production through endothelial-to-hematopoietic transition requires suitable developmental signals, but how these signals are accurately regulated remains incompletely understood. Cytoplasmic polyadenylation, which is one of the posttranscriptional regulations, plays a crucial role in RNA metabolism. Here, we report that Cpeb1b-mediated cytoplasmic polyadenylation is important for HSPC specification by translational control of Hedgehog (Hh) signaling during zebrafish early development. Cpeb1b is highly expressed in notochord and its deficiency results in defective HSPC production. Mechanistically, Cpeb1b regulates hemogenic endothelium specification by the Hedgehog–Vegf–Notch axis. We demonstrate that the cytoplasmic polyadenylation element motif-dependent interaction between Cpeb1b and shha messenger RNA (mRNA) in the liquid-like condensates, which are induced by Pabpc1b phase separation, is required for cytoplasmic polyadenylation of shha mRNA. Intriguingly, the cytoplasmic polyadenylation regulates translation but not stability of shha mRNA, which further enhances the Shha protein level and Hh signal transduction. Taken together, our findings uncover the role of Cpeb1b-mediated cytoplasmic polyadenylation in HSPC development and provide insights into how posttranscriptional regulation can direct developmental signals with high fidelity to translate them into cell fate transition.
Project description:Despite the importance of egg development to the female life cycle in Drosophila, global patterns of gene expression have not been examined in detail primarily due to the difficulty of synchronizing developmental stages. Entry into vitellogenesis is however an key stage of oogenesis, and by delaying entry past this control point, we have been able to investigate some of the transcriptional dynamics apparent before and after early egg formation over a 72 hour period.
Project description:Cell fate transitions involve rapid changes of gene expression patterns and global chromatin remodeling, yet the underlying regulatory pathways remain incompletely understood. Here, we used transcription-factor induced reprogramming of somatic cells into pluripotent cells to screen for novel regulators of cell fate change. We identified the RNA processing factor Nudt21, a component of the pre-mRNA cleavage and polyadenylation complex, as a potent barrier to reprogramming. Importantly, suppression of Nudt21 not only enhanced the generation of induced pluripotent stem cells but also facilitated the conversion of fibroblasts into trophoblast stem cells and delayed the differentiation of myeloid precursor cells into macrophages, suggesting a broader role for Nudt21 in restricting cell fate change. Polyadenylation site sequencing (PAS-seq) revealed that Nudt21 directs differential polyadenylation of over 1,500 transcripts in cells acquiring pluripotency. While only a fraction of these transcripts changed expression at the protein level, this fraction was strongly enriched for chromatin regulators, including components of the PAF, polycomb, and trithorax complexes. Co-suppression analysis further suggests that these chromatin factors are largely responsible for Nudt21’s effect on reprogramming, providing a mechanistic basis for our observations. Collectively, our data uncover Nudt21 as a novel post-transcriptional regulator of mammalian cell fate and establish a direct, previously unappreciated link between alternative polyadenylation and chromatin signaling.
Project description:Cytoplasmic polyadenylation is a mechanism to promote mRNA translation in a wide variety of biological contexts.The conserved RNA-binding protein family CPEB has been shown to mediate canonical cytoplasmic polyadenylation of target transcripts. We have previously reported evidence for RNA-interference factor Dicer-2 as a component of a non-canonical complex, that operates independent of CPEB in Drosophila. In this study, we investigate Dicer-2 mRNA targets and protein co-factors in cytoplasmic polyadenylation. Using RIP‐Seq analysis we identify hundreds of potential Dicer-2 target transcripts, ~60% of which were previously found as targets of the cytoplasmic poly(A) polymerase Wispy, suggesting widespread roles of Dicer-2 in cytoplasmic polyadenylation. Large-scale immunoprecipitation and mass spectrometry revealed Ataxin-2 and Twenty-four among the high-confidence interactors of Dicer-2. Complex analyses indicated that both factors form an RNA‐independent complex with Dicer‐2, and mediate interactions of Dicer‐2 with Wispy. Functional poly(A)‐test analyses showed that Twenty‐four and Ataxin-2 are required for cytoplasmic polyadenylation of a subset of Dicer‐2 targets. Our results reveal components of a novel cytoplasmic polyadenylation complex that operates during Drosophila early embryogenesis.
Project description:Cytoplasmic polyadenylation is a mechanism to promote mRNA translation in a wide variety of biological contexts. A canonical complex centered around the conserved RNA-binding protein family CPEB has been shown to be responsible for this process. We have previously reported evidence for an alternative non-canonical, CPEB-independent complex in Drosophila, of which the RNA-interference factor Dicer-2 is a component. Here, we investigate Dicer-2 mRNA targets and protein co-factors in cytoplasmic polyadenylation. Using RIP-Seq analysis we identify hundreds of novel Dicer-2 target transcripts, ~50% of which were previously found as targets of the cytoplasmic poly(A) polymerase Wispy, suggesting widespread roles of Dicer-2 in cytoplasmic polyadenylation. Large-scale immunoprecipitation revealed Ataxin-2 and Twenty-four among the high-confidence interactors of Dicer-2. Functional analysis indicate that both factors form an RNA-independent complex with Dicer-2, and are required for cytoplasmic polyadenylation of Dicer-2 targets. Our results reveal the composition of a novel cytoplasmic polyadenylation complex that operates during Drosophila early embryogenesis.
Project description:Immediate early genes (IEGs) represent a unique class of genes with rapid induction kinetics and transient expression patterns, which requires IEG mRNAs to be short-lived. Here, we establish cytoplasmic polyadenylation element-binding protein 4 (CPEB4) as a major determinant of IEG mRNA instability. We identified human CPEB4 as an RNA-binding protein (RBP) with enhanced association to poly(A) RNA upon inhibition of class I histone deacetylases (HDACs), which is known to cause widespread degradation of poly(A)-containing mRNA. Photoactivatable ribonucleoside-enhanced crosslinking and immunoprecipitation (PAR-CLIP) analysis using endogenously tagged CBEP4 in HeLa cells revealed that CPEB4 preferentially binds to the 3' untranslated region (UTR) of IEG mRNAs, at U-rich sequence motifs located in close proximity to the poly(A) site. By transcriptome-wide mRNA decay measurements, we found that the strength of CPEB4 binding correlates with short mRNA half-lives, and that loss of CPEB4 expression leads to the stabilization of IEG mRNAs. Further, we demonstrate that CPEB4 mediates mRNA degradation by recruitment of the evolutionarily conserved CCR4-NOT complex, the major eukaryotic deadenylase. While CPEB4 is primarily known for its ability to stimulate cytoplasmic polyadenylation, our findings establish an additional function for CPEB4 as an RBP that enhances the degradation of short-lived IEG mRNAs.