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Arenas-Mena C, Akin S. Widespread priming of transcriptional regulatory elements by incipient accessibility or RNA polymerase II pause in early embryos of the sea urchin Strongylocentrotus purpuratus. Genetics 2023; 225:iyad145. [PMID: 37551428 PMCID: PMC10789315 DOI: 10.1093/genetics/iyad145] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2023] [Revised: 05/17/2023] [Accepted: 07/25/2023] [Indexed: 08/09/2023] Open
Abstract
Transcriptional regulatory elements (TREs) are the primary nodes that control developmental gene regulatory networks. In embryo stages, larvae, and adult differentiated red spherule cells of the sea urchin Strongylocentrotus purpuratus, transcriptionally engaged TREs are detected by Precision Run-On Sequencing (PRO-seq), which maps genome-wide at base pair resolution the location of paused or elongating RNA polymerase II (Pol II). In parallel, TRE accessibility is estimated by the Assay for Transposase-Accessible Chromatin using Sequencing (ATAC-seq). Our analysis identifies surprisingly early and widespread TRE accessibility in 4-cell cleavage embryos that is not necessarily followed by concurrent or subsequent transcription. TRE transcriptional differences identified by PRO-seq provide more contrast among embryonic stages than ATAC-seq accessibility differences, in agreement with the apparent excess of accessible but inactive TREs during embryogenesis. Global TRE accessibility reaches a maximum around the 20-hour late blastula stage, which coincides with the consolidation of major embryo regionalizations and peak histone variant H2A.Z expression. A transcriptional potency model based on labile nucleosome TRE occupancy driven by DNA sequences and the prevalence of histone variants is proposed in order to explain the basal accessibility of transcriptionally inactive TREs during embryogenesis. However, our results would not reconcile well with labile nucleosome models based on simple A/T sequence enrichment. In addition, a large number of distal TREs become transcriptionally disengaged during developmental progression, in support of an early Pol II paused model for developmental gene regulation that eventually resolves in transcriptional activation or silencing. Thus, developmental potency in early embryos may be facilitated by incipient accessibility and transcriptional pause at TREs.
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Affiliation(s)
- Cesar Arenas-Mena
- Department of Biology, College of Staten Island, City University of New York (CUNY), 2800 Victory Boulevard, Staten Island, NY, 10314, USA
- PhD Programs in Biology and Biochemistry at the City University of New York (CUNY), Graduate Center, 365 Fifth Avenue, New York, NY, 10016, USA
| | - Serhat Akin
- Department of Biology, College of Staten Island, City University of New York (CUNY), 2800 Victory Boulevard, Staten Island, NY, 10314, USA
- PhD Program in Biology at the City University of New York (CUNY), Graduate Center, 365 Fifth Avenue, New York, NY, 10016, USA
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Dijkwel Y, Tremethick DJ. The Role of the Histone Variant H2A.Z in Metazoan Development. J Dev Biol 2022; 10:jdb10030028. [PMID: 35893123 PMCID: PMC9326617 DOI: 10.3390/jdb10030028] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2022] [Revised: 06/12/2022] [Accepted: 06/23/2022] [Indexed: 12/10/2022] Open
Abstract
During the emergence and radiation of complex multicellular eukaryotes from unicellular ancestors, transcriptional systems evolved by becoming more complex to provide the basis for this morphological diversity. The way eukaryotic genomes are packaged into a highly complex structure, known as chromatin, underpins this evolution of transcriptional regulation. Chromatin structure is controlled by a variety of different epigenetic mechanisms, including the major mechanism for altering the biochemical makeup of the nucleosome by replacing core histones with their variant forms. The histone H2A variant H2A.Z is particularly important in early metazoan development because, without it, embryos cease to develop and die. However, H2A.Z is also required for many differentiation steps beyond the stage that H2A.Z-knockout embryos die. H2A.Z can facilitate the activation and repression of genes that are important for pluripotency and differentiation, and acts through a variety of different molecular mechanisms that depend upon its modification status, its interaction with histone and nonhistone partners, and where it is deposited within the genome. In this review, we discuss the current knowledge about the different mechanisms by which H2A.Z regulates chromatin function at various developmental stages and the chromatin remodeling complexes that determine when and where H2A.Z is deposited.
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Arenas-Mena C, Miljovska S, Rice EJ, Gurges J, Shashikant T, Wang Z, Ercan S, Danko CG. Identification and prediction of developmental enhancers in sea urchin embryos. BMC Genomics 2021; 22:751. [PMID: 34666684 PMCID: PMC8527612 DOI: 10.1186/s12864-021-07936-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2021] [Accepted: 06/28/2021] [Indexed: 11/21/2022] Open
Abstract
Background The transcription of developmental regulatory genes is often controlled by multiple cis-regulatory elements. The identification and functional characterization of distal regulatory elements remains challenging, even in tractable model organisms like sea urchins. Results We evaluate the use of chromatin accessibility, transcription and RNA Polymerase II for their ability to predict enhancer activity of genomic regions in sea urchin embryos. ATAC-seq, PRO-seq, and Pol II ChIP-seq from early and late blastula embryos are manually contrasted with experimental cis-regulatory analyses available in sea urchin embryos, with particular attention to common developmental regulatory elements known to have enhancer and silencer functions differentially deployed among embryonic territories. Using the three functional genomic data types, machine learning models are trained and tested to classify and quantitatively predict the enhancer activity of several hundred genomic regions previously validated with reporter constructs in vivo. Conclusions Overall, chromatin accessibility and transcription have substantial power for predicting enhancer activity. For promoter-overlapping cis-regulatory elements in particular, the distribution of Pol II is the best predictor of enhancer activity in blastula embryos. Furthermore, ATAC- and PRO-seq predictive value is stage dependent for the promoter-overlapping subset. This suggests that the sequence of regulatory mechanisms leading to transcriptional activation have distinct relevance at different levels of the developmental gene regulatory hierarchy deployed during embryogenesis. Supplementary Information The online version contains supplementary material available at 10.1186/s12864-021-07936-0.
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Affiliation(s)
- César Arenas-Mena
- College of Staten Island, The City University of New York (CUNY), Staten Island, NY, 10314, USA. .,Programs in Biology and Biochemistry, The Graduate Center, CUNY, New York, NY, 10016, USA.
| | - Sofija Miljovska
- Department of Biology, New York University, New York, NY, 10003, USA
| | - Edward J Rice
- Baker Institute for Animal Health, College of Veterinary Medicine, Cornell University, Ithaca, NY, 14853, USA
| | - Justin Gurges
- College of Staten Island, The City University of New York (CUNY), Staten Island, NY, 10314, USA
| | - Tanvi Shashikant
- Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA, USA
| | - Zihe Wang
- College of Staten Island, The City University of New York (CUNY), Staten Island, NY, 10314, USA
| | - Sevinç Ercan
- Department of Biology, New York University, New York, NY, 10003, USA.,Center for Genomics and Systems Biology, New York University, New York, NY, 10003, USA
| | - Charles G Danko
- Baker Institute for Animal Health, College of Veterinary Medicine, Cornell University, Ithaca, NY, 14853, USA.,Department of Biomedical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY, 14853, USA
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Buckley KM, Dong P, Cameron RA, Rast JP. Bacterial artificial chromosomes as recombinant reporter constructs to investigate gene expression and regulation in echinoderms. Brief Funct Genomics 2019; 17:362-371. [PMID: 29045542 DOI: 10.1093/bfgp/elx031] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Genome sequences contain all the necessary information-both coding and regulatory sequences-to construct an organism. The developmental process translates this genomic information into a three-dimensional form. One interpretation of this translation process can be described using gene regulatory network (GRN) models, which are maps of interactions among regulatory gene products in time and space. As high throughput investigations reveal increasing complexity within these GRNs, it becomes apparent that efficient methods are required to test the necessity and sufficiency of regulatory interactions. One of the most complete GRNs for early development has been described in the purple sea urchin, Strongylocentrotus purpuratus. This work has been facilitated by two resources: a well-annotated genome sequence and transgenes generated in bacterial artificial chromosome (BAC) constructs. BAC libraries played a central role in assembling the S. purpuratus genome sequence and continue to serve as platforms for generating reporter constructs for use in expression and regulatory analyses. Optically transparent echinoderm larvae are highly amenable to transgenic approaches and are therefore particularly well suited for experiments that rely on BAC-based reporter transgenes. Here, we discuss the experimental utility of BAC constructs in the context of understanding developmental processes in echinoderm embryos and larvae.
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Affiliation(s)
- Katherine M Buckley
- Department of Biological Sciences, George Washington University, Washington, DC, USA
| | - Ping Dong
- California Institute of Technology, California, USA
| | - R Andrew Cameron
- Beckman Institute Center for Computational Regulatory Genomics, California Institute for Technology, California, USA
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Lowe EK, Cuomo C, Arnone MI. Omics approaches to study gene regulatory networks for development in echinoderms. Brief Funct Genomics 2018; 16:299-308. [PMID: 28957458 DOI: 10.1093/bfgp/elx012] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Gene regulatory networks (GRNs) describe the interactions for a developmental process at a given time and space. Historically, perturbation experiments represent one of the key methods for analyzing and reconstructing a GRN, and the GRN governing early development in the sea urchin embryo stands as one of the more deeply dissected so far. As technology progresses, so do the methods used to address different biological questions. Next-generation sequencing (NGS) has become a standard experimental technique for genome and transcriptome sequencing and studies of protein-DNA interactions and DNA accessibility. While several efforts have been made toward the integration of different omics approaches for the study of the regulatory genome in many animals, in a few cases, these are applied with the purpose of reconstructing and experimentally testing developmental GRNs. Here, we review emerging approaches integrating multiple NGS technologies for the prediction and validation of gene interactions within echinoderm GRNs. These approaches can be applied to both 'model' and 'non-model' organisms. Although a number of issues still need to be addressed, advances in NGS applications, such as assay for transposase-accessible chromatin sequencing, combined with the availability of embryos belonging to different species, all separated by various evolutionary distances and accessible to experimental regulatory biology, place echinoderms in an unprecedented position for the reconstruction and evolutionary comparison of developmental GRNs. We conclude that sequencing technologies and integrated omics approaches allow the examination of GRNs on a genome-wide scale only if biological perturbation and cis-regulatory analyses are experimentally accessible, as in the case of echinoderm embryos.
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