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Gene expression in unfertilized eggs and the MBT stage of zebrafish embryos

ABSTRACT: Very little is known on the nature of epigenetic states in developing zebrafish despite its growing importance as a model organism in developmental biology. We report histone modifications on promoters of pluripotency genes in zebrafish embryos at the mid-late blastula transition (MBT+) stage. We identify three classes of expressed genes based on these profiles: (1) those with a promoter occupied by marks of active genes without any repressive marks; (2) those co-occupied by both activating and repressive modifications; of these genes, klf4 was notably found to be mosaically expressed in the embryo, possibly accounting for this epigenetic pattern; (3) those occupied by repressive marks with, surprisingly, little not acetylated H3K9 or H4. Culture of embryo-derived cells results in a switch from histone acetylation to K9 and K27 trimethylation on genes transcriptionally inactivated, resulting in a profile similar to that of fibroblasts. All promoters retain H3K4me3, indicating no correlation between H3K4me3 occupancy and gene expression. Our results illustrate a complex chromatin state on the promoter of pluripotency-associated genes in the zebrafish embryo, shortly after the embryonic genome is turned on. We assessed gene expression in unfertilized eggs and the MBT stage of zebrafish embryos (~ 3.5 hpf) using a 44K custom designed chip from Agilent (3 and 4 replicates, respectively). Genes of interest were extracted and evaluated according to expression dynamics and levels.

ORGANISM(S): Danio rerio

SUBMITTER: HÃ¥vard Aanes

PROVIDER: E-GEOD-20137 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Gene expression in unfertilized eggs and the MBT stage of zebrafish embryos

Project description:Very little is known on the nature of epigenetic states in developing zebrafish despite its growing importance as a model organism in developmental biology. We report histone modifications on promoters of pluripotency genes in zebrafish embryos at the mid-late blastula transition (MBT+) stage. We identify three classes of expressed genes based on these profiles: (1) those with a promoter occupied by marks of active genes without any repressive marks; (2) those co-occupied by both activating and repressive modifications; of these genes, klf4 was notably found to be mosaically expressed in the embryo, possibly accounting for this epigenetic pattern; (3) those occupied by repressive marks with, surprisingly, little not acetylated H3K9 or H4. Culture of embryo-derived cells results in a switch from histone acetylation to K9 and K27 trimethylation on genes transcriptionally inactivated, resulting in a profile similar to that of fibroblasts. All promoters retain H3K4me3, indicating no correlation between H3K4me3 occupancy and gene expression. Our results illustrate a complex chromatin state on the promoter of pluripotency-associated genes in the zebrafish embryo, shortly after the embryonic genome is turned on.

2010-02-03 | GSE20137 | GEO

Maternally inherited piRNAs silence transposons during Drosophila embryogenesis

Project description:The piRNA pathway controls transposon expression in animal germ cells, thereby ensuring genome stability over generations. piRNAs are maternally deposited and required for proper transposon silencing in adult offspring. However, a long-standing question in the field is the precise function of maternally deposited piRNAs and its associated factors during embryogenesis. Here, we probe the spatio-temporal expression patterns of several piRNA pathway components during early stages of development. Amongst those, factors required for transcriptional gene silencing (TGS) showed ubiquitous abundance in somatic and pole cells throughout the first half of embryogenesis. We further analysed the transcriptomes of various embryo stages and correlated these with the presence of selected chromatin marks. We found that a number of transposon families show bursts of transcription during early embryonic stages. Transposons heavily targeted by maternally deposited piRNAs accumulated repressive chromatin marks following their spike in expression. Furthermore, depletion of maternally deposited Piwi protein in early embryos resulted in increased expression of transposons targeted by inherited piRNAs and was accompanied by a strong loss of repressive chromatin marks at coding sequences. Overall, our data suggests a pivotal role for the piRNA pathway in transposon defence during Drosophila embryogenesis in somatic cells.

2021-07-26 | PXD022409 | Pride

Study of Mid-Blastula Transition of zebrafish embryos

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).

2011-10-12 | E-GEOD-32914 | biostudies-arrayexpress

Different transcriptional strategies for zygotic genome activation in Drosophila [ChIP-Seq]

Project description:During animal development, a fertilized egg is initially under the control of maternal products and only starts zygotic transcription after several cell divisions. In animals such as Xenopus, zebrafish and Drosophila, a massive increase in zygotic transcription occurs during the mid-blastula transition (MBT), when cells shift from rapid, synchronous cell divisions without gap phases to prolonged asynchronous divisions. Before MBT, only a few so-called pre-MBT genes are expressed. How transcription is set up during these early stages is poorly understood. For example, paused RNA Polymerase (Pol II) is frequently found at developmental control genes in mammalian embryonic stem cells and Drosophila embryos but when Pol II pausing is first established in the embryo is unknown. We have analyzed the genome-wide Pol II occupancy during the maternal-to-zygotic transition in hand-staged Drosophila embryos. The results show that massive Pol II recruitment and pausing is established during MBT. The ~100 genes that are transcribed before MBT are particularly short, consistent with a need for rapid transcription during these early cell divisions. Remarkably, most of these genes are transcribed without Pol II pausing and this correlates with a TATA-enriched promoter type. This suggests that distinct strategies are used for activation in the early Drosophila embryo and this may reflect general dynamic properties of promoters used throughout development. ChIP-seq for Pol II, TBP, H3K4me3, H3K27me3 and H3Ac in Drosophila embryos

2013-07-26 | E-GEOD-41700 | biostudies-arrayexpress

Different transcriptional strategies for zygotic genome activation in Drosophila [MNase-Seq]

2013-07-26 | E-GEOD-41686 | biostudies-arrayexpress

Marking of the genome by H3K4 methylation prior to embryonic gene activation

Project description:Early zebrafish embryo development proceeds first from a maternally transcribed and stored mRNAs, and zygotic gene activation (ZGA) is initiated at the mid-blastula transition (MBT; 1000-cell stage), 3.3 h post-fertilization. Very little is known on how the zygotic genome is programmed for transcriptional activation at the MBT. To start addressing this issue, we have mapped by ChIP-chip genome-wide promoter histone methylation (H3K4me3, H3K9me3, H3K27me3, H3K36me3) and RNA Pol II profiles before ZGA (256-cell stage; 2.5 hpf), during ZGA (MBT; 3.5 hpf)) and after ZGA (Post-MBT; 5.3 hpf) . We used a custom 2.1M probe HD promoter array (Nimblegen) for ChIP and input DNA hybridization. Peak detection was done using MA2C with P=10e-4 as cutoff. ChIP-chip experiments were performed from chromatin prepared by sonication after formaldehyde cross-linking, from embryos are the indicated developmental stages and ChIP DNA was hybridized onto the aforementioned Nimbegen promoter arrays.

2011-12-02 | E-GEOD-27314 | biostudies-arrayexpress

Zebrafish early embryos isolated nuclei and whole blastomeres LC-MSMS

Project description:Nuclear pore complex (NPC) structure and maturity changed during early development before MBT in zebrafish embryos. Aiming to further confirm the difference of NPCs among different stages during MZT, we first isolated nuclei from 32-cell and 512-cell stage embryos as most zygotic genes have not been transcribed at these two stages yet. The lysates from identical number (about 12,500 nuclei per stage) isolated nuclei were then trypsin-digested and fractionated, followed by high-resolution LC-MS/MS analysis on the Q-Exactive HF-X mass spectrometers using a label-free assay. Whole blastomeres from 32-cell and 512-cell were also prepared with yolk removal to serve as total protein profile control, and the same amount lysates were analyzed by high-resolution LC-MS/MS with TMT labelled. Each sample for MS analysis had two repeats. Correlation analysis revealed that the abundance ratio from isolated Nuclei and whole deyolking balstomeres did not correlate well, but samples in Nuclei or Whole blastomeres were well correlated. This result indicates the convincible sample preparation as well as the variability in nuclei composition in early developmental period before MBT.

2023-08-25 | PXD017896 | Pride

Differential transcript isoform usage pre- and post-zygotic genome activation in zebrafish

Project description:Zebrafish embryos are transcriptional silent until activation of the zygotic genome during the 10th cell cycle. Onset of transcription is followed by cellular and morphological changes involving cell speciation and gastrulation. Previous genome-wide surveys of transcriptional changes only assessed gene expression levels; however, recent studies have shown the necessity to map isoform-specific transcriptional changes. Here we perform isoform discovery and quantification on transcriptome sequences from before and after zebrafish zygotic genome activation (ZGA). We identify novel isoforms and isoform switches during ZGA for genes related to cell adhesion, pluripotency and DNA methylation. Isoform switching events include alternative splicing and changes in transcriptional start sites and in 3’ untranslated regions. New isoforms are identified even for well-characterized genes such as pou5f1, sall4 and dnmt1. Genes involved in cell-cell interactions such as f11r and magi1 display isoform switches with alterations of coding sequences. We also detect over 1000 transcripts that acquire a longer 3’ terminal exon when transcribed zygotically relative to the maternal transcript counterparts. ChIP-seq data mapped onto skipped exon events reveals a correlation between histone H3K36trimethylation peaks and the skipped exons, suggesting epigenetic marks being part of alternative splicing regulation. The novel isoforms and isoform switches reported here include regulators of the transcriptional, cellular and morphological changes taking place around ZGA. Our data display an array of isoform-related functional changes and represent a valuable resource complementary to existing early embryo transcriptomes. Examination H3K36me3 in zebrafish whole embryos at the Post-MBT stage

2012-11-01 | E-GEOD-40629 | biostudies-arrayexpress

Marking of the genome by H3K4 methylation prior to embryonic gene activation

2011-12-02 | GSE27314 | GEO

Chromatin signature of embryonic pluripotency is established during zygotic genome activation [Danio rerio]

Project description:[PROJECT] After fertilization the embryonic genome is inactive until transcription is initiated during the maternal-zygotic transition (MZT). This universal process coincides with the formation of pluripotent cells, which in mammals can be used to generate embryonic stem (ES) cells. To study the changes in chromatin structure that accompany zygotic genome activation and pluripotency, we mapped the genomic locations of histone H3 modifications before and after MZT in zebrafish embryos. Repressive H3 lysine 27 trimethylation (H3K27me3) and activating H3 lysine 4 trimethylation (H3K4me3) are only detected after MZT. H3K4me3 marks more than 80% of genes, including many developmental regulatory genes that are also occupied by H3K27me3. Sequential chromatin immunoprecipitation demonstrates that both methylation marks occupy the same promoter regions, revealing that the bivalent chromatin domains found in cultured ES cells also exist in embryos. In addition, we find a large group of genes that are monovalently marked by H3K4me3 but not H3K27me3. These H3K4me3 monovalent genes are neither expressed nor stably bound by RNA polymerase II. Closer inspection of in vitro data sets reveals similar monovalent H3K4me3 domains in ES cells. The analysis of an inducible transgene indicates that H3K4me3 domains can form in the absence of sequence-specific transcriptional activators or stable association with RNA pol II. These results suggest that bivalent and monovalent domains might poise embryonic genes for activation and that the chromatin profile associated with pluripotency is established during MZT. [SAMPLES] ChIPchip analysis of histone modifications (H3K4me3, H3K27me3, H3K36me3) and RNA polymerase II in pre MZT (256-cell) and post MZT (4hpf; dome/30% epiboly) wt zebrafish embryos. H3K4me3, H3K27me3, H3K36me3 and PolII ChIP-chip at 256 cell stage (one replicate) and 4hpf (dome/30% epiboly) (two replicates)

2010-01-25 | E-GEOD-20023 | biostudies-arrayexpress

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