Abstract
Chicken erythrocytes are nucleated cells often considered to be transcriptionally inactive, although the epigenetic changes and chromatin remodeling that would mediate transcriptional repression and the extent of gene silencing during avian terminal erythroid differentiation are not fully understood. Here, we characterize the changes in gene expression, chromatin accessibility, genome organization and chromatin nuclear disposition during the terminal stages of erythropoiesis in chicken and uncover complex chromatin reorganization at different genomic scales. We observe a robust decrease in transcription in erythrocytes, but a set of genes maintains their expression, including genes involved in RNA polymerase II (Pol II) promoter-proximal pausing. Erythrocytes exhibit a reoriented nuclear architecture, with accessible chromatin positioned towards the nuclear periphery together with the paused RNA Pol II. In erythrocytes, chromatin domains are partially lost genome-wide, except at minidomains retained around paused promoters. Our results suggest that promoter-proximal pausing of RNA Pol II contributes to the transcriptional regulation of the erythroid genome and highlight the role of RNA polymerase in the maintenance of local chromatin organization.
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Data availability
All reads generated were mapped against the chicken genome version GRCg6a. All datasets generated in this study have been deposited as a super series at GEO with accession number GSE206194. Source data are provided with this paper.
Change history
17 April 2024
A Correction to this paper has been published: https://doi.org/10.1038/s41594-024-01307-5
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Acknowledgements
A.P.-P. is supported by CONAHCyT scholarship no. 822335. This work was supported by PAPIIT grants no. IN207319 and no. IN210323 and by CONAHCyT grants no. 303068, no. 15758 and no. 137721. The funders had no role in study design, data collection and analysis, decision to publish or preparation of the manuscript. We thank F. Recillas-Targa for kind donation of the HD3 erythroblast cell line. We thank the Molecular Biology Unit, the Microscopy Unit and the Bioinformatics Unit at the IFC, in particular R. Rincón-Heredia and A. Cesar Poot-Hernández for advice on image processing and genomic data analysis, respectively. We thank the Animal Facility at the IFC, in particular C. Rivera-Cerecedo and H. Malagón-Rivera. We thank the Supercomputing Unit at LANCIS, in particular R. García-Herrera for access to the computer cluster. We thank R. Saldaña-Meyer and M. Escamilla Del Arenal for helpful discussion on the results obtained in this work.
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A.P.-P. and M.F.-M. designed the project, analyzed and discussed the data, and wrote the manuscript with comments from all authors. A.P.-P. performed and analyzed ATAC-see, ATAC-seq and Hi-C experiments and immunostainings. S.C.-G. performed and analyzed the RNA-seq and ChIP–seq as well as the ChIP–qPCR experiments and western blots. A.S.-G. performed and analyzed the initial Hi-C and RT–qPCR experiments. A.A.-L. and K.J.-L. helped with data analysis, X.C. provided the Tn5 ATTO 590N enzyme and R.P.-M. helped with experiments and provided laboratory assistance to all authors. All authors contributed to the discussion of the results.
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Extended data
Extended Data Fig. 1 Validation of ATAC-see and chromatin reorientation in aRBC.
a, Imaging of open chromatin by ATAC-see (red) and DAPI (blue, nuclei) in chicken fibroblasts. A negative control of ATAC-see in presence of EDTA 50 mM shows no incorporation of the fluorophore. Representative images from two independent experiments are shown. b, ATAC-see signal average intensity per nucleus in chicken erythrocytes. Boxplots with median (horizontal line), mean (+), 25th and 75th percentiles (boxes), and whiskers denoting the 10th and 90th percentile from 50 nuclei from two independent experiments are shown. P values based on one-way ANOVA followed by Tukey’s post-hoc test are indicated. c, Representative images from two ATAC-see experiments in aRBC. Brightest pixels enriched in ATAC-see (red) or DAPI (blue) are shown on the right. d, Pearson’s correlation score between ATAC-see, DAPI or H3K9me3 signal intensity and the distance to the nuclear rim (n = 50 nuclei from two independent replicates). Scatter dot plots show mean values +/− SD. e, Fluorescence imaging of Lamin B1 (green) and DAPI. In every case, maximal projections of three-dimensional (3D) stacks are presented. Representative images from two replicates are shown. Scale bar = 5 µm.
Extended Data Fig. 2 Characterization of the erythroid transcriptome.
a, Spearman correlation heatmap of RNA-seq replicates. b, Venn diagram of expressed genes in fibroblasts and erythroid cells. c, Relative expression of GAPDH and HBBA measured by RT-qPCR, triplicates from two biological replicates are presented. For aRBC and fibroblasts this means independent samples from two different animals, for eRBC this means two independent RBC collection from approximately 20 embryos, and for erythroblasts this means two independent cell cultures. Data is presented as means +/− SD. P values indicated are based on one-way ANOVA analysis followed by Tukey’s post-hoc test d, Expression levels of the erythroid genes EPB41 and EPB42 measured by RNA-seq (up; n = 3 independent RNA-seq libraries) and RT-qPCR (down: n= same as c). Data is presented as means +/− SD with P values based on one-way ANOVA followed by Tukey’s post-hoc test. e, EU incorporation measured by fluorescence intensity after 6 hours of incubation with EU (n = 50 nuclei from three independent Click-iT experiments). P values based on one-way ANOVA analysis followed by Kruskal-Wallis post hoc test are presented. f, MA plots of differentially expressed genes between eRBC and erythroblasts, and aRBC and erythroblasts. g, GO terms enriched in upregulated genes from f. Analysis was performed using Fisher’s exact test and the default multiple-hypotheses testing method (g:SCS) on gProfiler.
Extended Data Fig. 3 Chicken erythrocytes retain accessible paused promoters.
a, Spearman correlation heatmap of ATAC-seq replicates. b, Example of the preserved accessibility of the promoter of CTCF despite no transcriptional activity detected by RNA-seq. c, Representative images of DAPI and RNA pol II Ser2-P immunofluorescence from two replicates. Maximal projections of three-dimensional (3D) stacks are presented. Scale bar = 5 µm. Average signal intensity of RNA pol II Ser5-P (d,) and Ser2-P (e,) signal average intensity per nucleus in chicken erythrocytes. Boxplots with median (horizontal line), mean (+), 25th and 75th percentiles (boxes), and whiskers denoting the 10th and 90th percentile from 50 nuclei from two independent experiments are shown. P values based on one-way ANOVA followed by Tukey’s post-hoc test are presented. Pearson’s correlation score between RNA Pol II Ser-5 (f,) and Ser-2 (g,) signal intensity and the distance to the nuclear rim (n = 50 nuclei from two independent replicates). Scatter dot plots show mean values +/− SD. h, RNA pol II Ser5-Pand DAPI intensity is presented as a function of distance to the nuclear periphery. Individual tracks for 50 nuclei are presented in lighter colors and the mean intensity is presented in bold. i, RNA pol II Ser2-P and DAPI intensity is presented as a function of distance to the nuclear periphery. Individual tracks for 50 nuclei are presented in lighter colors and the mean intensity is presented in bold.
Extended Data Fig. 4 ChIP-qPCR confirms RNA Pol II Ser-5 occupancy of promoters of genes. that are not expressed in aRBC.
a, ATAC-seq, RNA Pol II Ser5-P ChIP-seq, and RNA-seq tracks of HTATSF1, GTF2H5, PCID2, and SOX2. b, ChIP-qPCR against RNA pol II Ser5-P. ATAC-seq peaks at the promoter of HTATSF1, GTF2H5 and PCID2 were analyzed. Fold enrichment was calculated against amplification in the promoter of SOX2. SOX2 enrichment was calculated against input. Mean +/− SD from 4 replicates is presented. Statistical differences against a mock control were calculated with a two-tailed t-test.
Extended Data Fig. 5 Erythroid mini domains retain local structure around open chromatin and paused genes.
a, Pearson correlation heatmap between Hi-C replicates at 50 Kb resolution. b, Hi-C contact matrices from eRBC and aRBC (3: 24.5–28 Mb) and examples of mini domains identified. ATAC-seq and RNA-seq tracks are plotted below. c, Western blot for CTCF and SMC1 proteins for all cell types. Histone 3 (H3) was used as the loading control. Representative results from two experiments are presented. d, RNA-seq RPKM count inside chromatin domains or a set of random regions of the same size in fibroblasts (n = 2,373 domains), erythroblasts (n = 2,562), eRBC (n = 916), and aRBC (903). Boxplots show median (horizontal line), mean (+), 25th and 75th percentiles (boxes), and whiskers denote the 1st and 99th percentiles. P values based on one-way ANOVA followed by Kruskal-Wallis post hoc test are stated.
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Penagos-Puig, A., Claudio-Galeana, S., Stephenson-Gussinye, A. et al. RNA polymerase II pausing regulates chromatin organization in erythrocytes. Nat Struct Mol Biol 30, 1092–1104 (2023). https://doi.org/10.1038/s41594-023-01037-0
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DOI: https://doi.org/10.1038/s41594-023-01037-0