scholarly journals Early genome activation in Drosophila is extensive with an initial tendency for aborted transcripts and retained introns

2018 ◽  
Author(s):  
Jamie C Kwasnieski ◽  
Terry L Orr-Weaver ◽  
David P Bartel
Keyword(s):  
Transposable Element ◽  
Middle Part ◽  
Gene Products ◽  
Cell Divisions ◽  
Zygotic Gene ◽  
Initial Tendency ◽  
A Minor ◽  
Retained Introns ◽  
Genome Activation ◽  
Zygotic Genome

AbstractControl of metazoan embryogenesis shifts from maternal to zygotic gene products as the zygotic genome becomes transcriptionally activated. In Drosophila, zygotic genome activation (ZGA) begins with a minor wave, but technical challenges have hampered the identification of early transcripts or obscured the onset of their transcription. Here, we develop an approach to isolate transcribed mRNAs and apply it over the course of the minor wave and the start of the major wave of Drosophila ZGA. Our results increase known genes of the minor wave by 10 fold and show that this wave is continuous and gradual. Transposable-element mRNAs are also produced, but discontinuously. Genes in the early and middle part of the minor wave are short with few if any introns, and their transcripts are frequently aborted and tend to have retained introns, suggesting that inefficient splicing as well as rapid cell divisions constrain the lengths of early transcripts.

scholarly journals The miR-430 locus with extreme promoter density is a transcription body organizer, which facilitates long range regulation in zygotic genome activation

2021 ◽  
Author(s):  
Yavor Hadzhiev ◽  
Lucy Wheatley ◽  
Ledean Cooper ◽  
Federico Ansaloni ◽  
Celina Whalley ◽  
...  
Keyword(s):  
Rna Polymerase Ii ◽  
Gene Cluster ◽  
Core Promoter ◽  
Single Copy ◽  
Early Embryo ◽  
Zygotic Genome Activation ◽  
Pol Ii ◽  
A Minor ◽  
Genome Activation ◽  
Zygotic Genome

In anamniote embryos the major wave of zygotic genome activation (ZGA) starts during the mid-blastula transition. This major wave of ZGA is facilitated by several mechanisms, including dilution of repressive maternal factors and accumulation of activating transcription factors during the fast cell division cycles preceding the mid-blastula transition. However, a set of genes escape global genome repression and are activated substantially earlier, during what is called, the minor wave of genome activation. While the mechanisms underlying the major wave of genome activation have been studied extensively, the minor wave of genome activation is little understood. In zebrafish the earliest expressed RNA polymerase II (Pol II) transcribed genes are activated in a pair of large transcription bodies depleted of chromatin, abundant in elongating Pol II and nascent RNAs (Hadzhiev et al., 2019; Hilbert et al., 2021). This transcription body includes the miR-430 gene cluster required for maternal mRNA clearance. Here we explored the genomic, chromatin organisation and cis-regulatory mechanisms of the minor wave of genome activation occurring in the transcription body. By long read genome sequencing we identified a remarkable cluster of miR-430 genes with over 300 promoters and spanning 0.6 Mb, which represent the highest promoter density of the genome. We demonstrate that the miR-430 gene cluster is required for the formation of the transcription body and acts as a transcription organiser for minor wave activation of a set of zinc finger genes scattered on the same chromosome arm, which share promoter features with the miR-430 cluster. These promoter features are shared among minor wave genes overall and include the TATA-box and sharp transcription start site profile. Single copy miR-430 promoter transgene reporter experiments indicate the importance of promoter-autonomous mechanisms regulating escape from global repression of the early embryo. These results together suggest that formation of the transcription body in the early embryo is the result of high promoter density coupled to a minor wave-specific core promoter code for transcribing key minor wave ZGA genes, which are required for the overhaul of the transcriptome during early embryonic development.

scholarly journals Early genome activation in Drosophila is extensive with an initial tendency for aborted transcripts and retained introns

2019 ◽  
Vol 29 (7) ◽  
pp. 1188-1197 ◽  
Author(s):  
Jamie C. Kwasnieski ◽  
Terry L. Orr-Weaver ◽  
David P. Bartel
Keyword(s):  
Initial Tendency ◽  
Retained Introns ◽  
Genome Activation

scholarly journals Transcriptional Activation of Arabidopsis Zygotes Is Required for Initial Cell Divisions

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Ping Kao ◽  
Michael D. Nodine
Keyword(s):  
Transcriptional Activation ◽  
Gene Products ◽  
Zygotic Genome Activation ◽  
Microscopy Technique ◽  
Early Embryos ◽  
Maternal To Zygotic Transition ◽  
Parental Gene ◽  
Active Transcription ◽  
Genome Activation ◽  
Zygotic Genome

AbstractCommonly referred to as the maternal-to-zygotic transition, the shift of developmental control from maternal-to-zygotic genomes is a key event during animal and plant embryogenesis. Together with the degradation of parental gene products, the increased transcriptional activities of the zygotic genome remodels the early embryonic transcriptome during this transition. Although evidence from multiple flowering plants suggests that zygotes become transcriptionally active soon after fertilization, the timing and developmental requirements of zygotic genome activation in Arabidopsis thaliana (Arabidopsis) remained a matter of debate until recently. In this report, we optimized an expansion microscopy technique for robust immunostaining of Arabidopsis ovules and seeds. This enabled the detection of marks indicative of active transcription in zygotes before the first cell division. Moreover, we employed a live-imaging culture system together with transcriptional inhibitors to demonstrate that such active transcription is physiologically required in zygotes and early embryos. Our results indicate that zygotic genome activation occurs soon after fertilization and is required for the initial zygotic divisions in Arabidopsis.

scholarly journals Transcriptional Activation of Arabidopsis Zygotes Is Required for Their Initial Division

2019 ◽  
Author(s):  
Ping Kao ◽  
Michael Nodine
Keyword(s):  
Transcriptional Activation ◽  
Culture System ◽  
Gene Products ◽  
Zygotic Genome Activation ◽  
Microscopy Technique ◽  
Maternal To Zygotic Transition ◽  
Parental Gene ◽  
Active Transcription ◽  
Genome Activation ◽  
Zygotic Genome

SUMMARYCommonly referred to as the maternal-to-zygotic transition, the shift of developmental control from maternal-to-zygotic genomes is a key event during animal and plant embryogenesis. Together with the degradation of parental gene products, the increased transcriptional activities of the zygotic genome remodels the early embryonic transcriptome during this transition. Although evidence from multiple flowering plants suggests that zygotes become transcriptionally active soon after fertilization, the timing and developmental requirements of zygotic genome activation in Arabidopsis thaliana (Arabidopsis) remained a matter of debate until recently. In this report, we optimized an expansion microscopy technique for robust immunostaining of Arabidopsis ovules and seeds. This enabled the detection of marks indicative of active transcription in zygotes before the first cell division. Moreover, we employed a live-imaging culture system together with transcriptional inhibitors to demonstrate that such active transcription is required in zygotes. Our results indicate that zygotic genome activation occurs soon after fertilization and is physiologically required prior to the initial zygotic division in Arabidopsis.

scholarly journals The DNA-to-cytoplasm ratio broadly activates zygotic gene expression in Xenopus

2021 ◽  
Author(s):  
David Jukam ◽  
Rishabh Kapoor ◽  
Aaron F Straight ◽  
Jan Skotheim
Keyword(s):  
Cycle Duration ◽  
Zygotic Genome Activation ◽  
Maternal Genome ◽  
Tropicalis Genome ◽  
Nuclear Component ◽  
Zygotic Gene ◽  
Component C ◽  
Genome Activation ◽  
Zygotic Genome

In multicellular animals, the first major event after fertilization is the switch from maternal to zygotic control of development. During this transition, zygotic gene transcription is broadly activated in an otherwise quiescent genome in a process known as zygotic genome activation (ZGA). In fast developing embryos, ZGA often overlaps with the slowing of initially synchronous cell divisions at the mid-blastula transition (MBT). Initial studies of the MBT led to the nuclear-to-cytoplasmic ratio model where MBT timing is regulated by the exponentially increasing amounts of some nuclear component N titrated against a fixed cytoplasmic component C. However, more recent experiments have been interpreted to suggest that ZGA is independent of the N/C ratio. To determine the role of the N/C ratio in ZGA, we generated Xenopus frog embryos with ~3-fold differences in genomic DNA (i.e., N) by using X. tropicalis sperm to fertilize X. laevis eggs with or without their maternal genome. Resulting embryos have otherwise identical X. tropicalis genome template amounts, embryo sizes, and X. laevis maternal environments. We used the X. tropicalis paternally derived mRNA to identify a high confidence set of exclusively zygotic transcripts. Both ZGA and the increase in cell cycle duration are delayed in embryos with ~3-fold less DNA per cell. Thus, DNA is an important component of the N/C ratio, which is indeed a critical regulator of zygotic genome activation in Xenopus embryos.

Expression of the HSP 70.1 gene, a landmark of early zygotic activity in the mouse embryo, is restricted to the first burst of transcription

Development ◽  
1995 ◽  
Vol 121 (1) ◽  
pp. 113-122 ◽  
Author(s):  
E. Christians ◽  
E. Campion ◽  
E.M. Thompson ◽  
J.P. Renard
Keyword(s):  
Dna Replication ◽  
Mouse Embryo ◽  
Culture Conditions ◽  
Hsp 70 ◽  
Cell Stage ◽  
Embryonic Genome ◽  
Genome Activation ◽  
Alpha Amanitin ◽  
Zygotic Genome

Activation of the mouse embryonic genome at the 2-cell stage is characterized by the synthesis of several alpha-amanitin-sensitive polypeptides, some of which belong to the multigenic hsp 70 family. In the present work we show that a member of this family, the HSP 70.1 gene, is highly transcribed at the onset of zygotic genome activation. Transcription of this gene began as early as the 1-cell stage. Expression of the gene continued through the early 2-cell stage but was repressed before the completion of the second round of DNA replication. During this period we observed that the level of transcription was modulated by in vitro culture conditions. The coincidence of repression of HSP70.1 transcription with the second round of DNA replication was not found for other transcription-dependent polypeptides synthesized at the 2-cell stage.

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