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. 2016 Nov 8;7(5):897-910.
doi: 10.1016/j.stemcr.2016.09.007. Epub 2016 Oct 13.

CNOT3-Dependent mRNA Deadenylation Safeguards the Pluripotent State

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Free PMC article

CNOT3-Dependent mRNA Deadenylation Safeguards the Pluripotent State

Xiaofeng Zheng et al. Stem Cell Reports. .
Free PMC article

Abstract

Poly(A) tail length and mRNA deadenylation play important roles in gene regulation. However, how they regulate embryonic development and pluripotent cell fate is not fully understood. Here we present evidence that CNOT3-dependent mRNA deadenylation governs the pluripotent state. We show that CNOT3, a component of the Ccr4-Not deadenylase complex, is required for mouse epiblast maintenance. It is highly expressed in blastocysts and its deletion leads to peri-implantation lethality. The epiblast cells in Cnot3 deletion embryos are quickly lost during diapause and fail to outgrow in culture. Mechanistically, CNOT3 C terminus is required for its interaction with the complex and its function in embryonic stem cells (ESCs). Furthermore, Cnot3 deletion results in increases in the poly(A) tail lengths, half-lives, and steady-state levels of differentiation gene mRNAs. The half-lives of CNOT3 target mRNAs are shorter in ESCs and become longer during normal differentiation. Together, we propose that CNOT3 maintains the pluripotent state by promoting differentiation gene mRNA deadenylation and degradation, and we identify poly(A) tail-length regulation as a post-transcriptional mechanism that controls pluripotency.

Keywords: embryonic stem cell; mRNA deadenylation; pluripotent state; pre-implantation development.

Figures

Figure 1
Figure 1
Cnot3 Is Required for Early Embryonic Development (A and B) Cnot3 expression in pre-implantation embryos. Expression was determined by qRT-PCR and plotted as mean ± SEM from three independent experiments (A) and immunofluorescence staining (B). Scale bar, 20 μm. (C) Immunofluorescence staining of CNOT3 in WT and Cnot3 deletion embryos at the indicated developmental stages. Scale bars, 20 μm. (D) Morphology of WT and Cnot3 deletion embryos at E6.5 and E7.5. Scale bars, 100 μm. (E) Morphology and OCT4 expression of Cnot3 deletion embryo at E6.5. Scale bars, 20 μm. (F) Numbers and genotypes of embryos collected at the indicated developmental stages. Numbers of morphologically abnormal embryos are listed in parentheses.
Figure 2
Figure 2
Cnot3 Deletion Impairs Epiblast Maintenance (A) Immunofluorescence staining of epiblast markers OCT4, NANOG, and trophectoderm marker CDX2 in WT and Cnot3 deletion embryos. Scale bars, 20 μm. (B) Total cell number and percentage of OCT4-, NANOG-, or CDX2-positive cells in WT and Cnot3 deletion embryos. Values were plotted as mean ± SEM from three independent experiments. (C) Epiblast cell outgrowth from WT and Cnot3 deletion blastocysts. White arrows, epiblast cells; black arrows, trophectoderm cells. Scale bars, 20 μm.
Figure 3
Figure 3
CNOT3 C-Terminal Domain Is Required for ESC Maintenance (A) Domain structure of mouse CNOT3. (B and C) Induction of Cnot3 deletion in Cnot3 cKO ESCs. Cells were treated with or without 4-OHT, and Cnot3 expression was determined by qRT-PCR (B) and western blot (C) at the indicated time points. Values were plotted as mean ± SEM from three independent experiments. (D) Interaction between CNOT3 fragments and CNOT1 or CNOT2. HA-tagged CNOT3 fragments were expressed in Cnot3 cKO ESCs and affinity purified by HA beads. Co-purified endogenous CNOT1 and CNOT2 were detected by western blot. Whole images of the same blots are shown in Figure S4B. (E–G) Rescue of the deletion phenotype by the overexpression of CNOT3 domains. Cnot3 cKO ESCs expressing various CNOT3 fragments were treated with or without 4-OHT. Changes in cellular morphology (E; scale bars, 200 μm), marker expression (F), and colony formation (G) were determined by imaging, qRT-PCR, and alkaline phosphatase staining, respectively. For qRT-PCR, relative expression was normalized by Actin and plotted as mean ± SEM from three independent experiments.
Figure 4
Figure 4
Cnot3 Deletion Leads to Increases in mRNA Half-Life and Steady-State Level (A) Gene expression changes after Cnot3 deletion in ESCs. Cnot3 cKO ESCs were treated with (KO) or without 4-OHT (WT). Cells were collected 72 hr after treatment and total RNAs were prepared for RNA-seq. (B) GO analysis of upregulated genes after Cnot3 deletion. Only selected GO categories were plotted. For complete list of enriched GO categories, see Table S2. (C and D) Increase in mRNA half-life in a subset of genes after Cnot3 deletion. Cnot3 cKO ESCs were treated with (KO) or without 4-OHT (WT). Actinomycin D was added 48 hr after treatment, and cells were collected at 0, 4, and 8 hr after actinomycin D addition for RNA-seq. (C) Frequency distribution and box plot for mRNA half-life in WT or KO samples. (D) Changes in mRNA half-life for genes down- or upregulated after Cnot3 deletion. (E) Venn diagrams showing the overlaps between genes with extended mRNA half-lives and those that are down- or upregulated after Cnot3 deletion.
Figure 5
Figure 5
Cnot3 Deletion Impairs Differentiation Gene Degradation (A) GSEA showing the enrichment for differentiation genes in the 194 CNOT3 target genes from Figure 2E. (B) Hierarchical clustering analysis showing the similarity in gene expression profiles after depletion of pluripotency genes and overexpression of differentiation genes (see Table S3 for gene expression datasets used in this plot). (C) Box plot for the half-lives of CNOT3 target genes, pluripotency genes, differentiation genes, and all genes in ESCs. (D) Box plot showing the changes in half-lives for CNOT3 target genes, pluripotency genes, differentiation genes, and all genes in ESCs during differentiation. (E) Metagene analysis and box plots (based on yellow highlighted regions in the metagene analysis) for H3K4me3 and H3K27me3 occupancy at the transcription start sites (TSS) of the CNOT3 target genes and all genes.
Figure 6
Figure 6
Cnot3 Deletion Increases Differentiation Gene mRNA Poly(A) Tail Lengths (A) Schematic drawing for mRNA fractionation based on poly(A) tail length. (B) Validation of the oligo(dT) fractionation method. Cnot3 cKO ESCs were treated with (KO) or without 4-OHT (WT) for 48 hr. The poly(A) standards were mixed with total RNAs extracted from the cells, and RNAs were fractionated by oligo(dT) beads. The distribution of each standard in each fraction (A0, A1, A2) was determined by qRT-PCR and plotted as mean ± SEM from three independent experiments. (C) Measurements of poly(A) tail length for the indicated genes by oligo(dT) fractionation. (D) Examination of mRNA stability for the indicated genes. Cnot3 cKO ESCs were treated with (KO) or without 4-OHT (WT) for 48 hr. Actinomycin D was added to the cells, and mRNA level was measured by qRT-PCR at the indicated time points. Relative expression values were plotted as mean ± SEM from three independent experiments. (E) Proposed model. CNOT3-dependent differentiation gene mRNA deadenylation and degradation plays a critical role in the maintenance of the pluripotent state. p < 0.05, ∗∗p < 0.01, ∗∗∗p < 0.001; ns, non-significant.

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