scholarly journals Taming active transposons at Drosophila telomeres: The interconnection between HipHop’s roles in capping and transcriptional silencing

PLoS Genetics ◽  
2021 ◽  
Vol 17 (11) ◽  
pp. e1009925
Author(s):  
Min Cui ◽  
Yaofu Bai ◽  
Kaili Li ◽  
Yikang S. Rong
Keyword(s):  
Genome Stability ◽  
Germline Development ◽  
Checkpoint Activation ◽  
Capping Protein ◽  
Poor Region ◽  
Selfish Element ◽  
Telomere Capping ◽  
Essential Function ◽  
Embryonic Arrest ◽  
Genetic Results

Drosophila chromosomes are elongated by retrotransposon attachment, a process poorly understood. Here we characterized a mutation affecting the HipHop telomere-capping protein. In mutant ovaries and the embryos that they produce, telomere retrotransposons are activated and transposon RNP accumulates. Genetic results are consistent with that this hiphop mutation weakens the efficacy of HP1-mediated silencing while leaving piRNA-based mechanisms largely intact. Remarkably, mutant females display normal fecundity suggesting that telomere de-silencing is compatible with germline development. Moreover, unlike prior mutants with overactive telomeres, the hiphop stock does not over-accumulate transposons for hundreds of generations. This is likely due to the loss of HipHop’s abilities both to silence transcription and to recruit transposons to telomeres in the mutant. Furthermore, embryos produced by mutant mothers experience a checkpoint activation, and a further loss of maternal HipHop leads to end-to-end fusion and embryonic arrest. Telomeric retroelements fulfill an essential function yet maintain a potentially conflicting relationship with their Drosophila host. Our study thus showcases a possible intermediate in this arm race in which the host is adapting to over-activated transposons while maintaining genome stability. Our results suggest that the collapse of such a relationship might only occur when the selfish element acquires the ability to target non-telomeric regions of the genome. HipHop is likely part of this machinery restricting the elements to the gene-poor region of telomeres. Lastly, our hiphop mutation behaves as a recessive suppressor of PEV that is mediated by centric heterochromatin, suggesting its broader effect on chromatin not limited to telomeres.

scholarly journals Eukaryotic clamp loaders and unloaders in the maintenance of genome stability

2020 ◽  
Vol 52 (12) ◽  
pp. 1948-1958
Author(s):  
Kyoo-young Lee ◽  
Su Hyung Park
Keyword(s):  
Dna Damage ◽  
Genomic Instability ◽  
Genome Stability ◽  
Critical Role ◽  
Nuclear Antigen ◽  
Checkpoint Activation ◽  
Sliding Clamp ◽  
Clamp Loaders ◽  
Factor C

AbstractEukaryotic sliding clamp proliferating cell nuclear antigen (PCNA) plays a critical role as a processivity factor for DNA polymerases and as a binding and acting platform for many proteins. The ring-shaped PCNA homotrimer and the DNA damage checkpoint clamp 9-1-1 are loaded onto DNA by clamp loaders. PCNA can be loaded by the pentameric replication factor C (RFC) complex and the CTF18-RFC-like complex (RLC) in vitro. In cells, each complex loads PCNA for different purposes; RFC-loaded PCNA is essential for DNA replication, while CTF18-RLC-loaded PCNA participates in cohesion establishment and checkpoint activation. After completing its tasks, PCNA is unloaded by ATAD5 (Elg1 in yeast)-RLC. The 9-1-1 clamp is loaded at DNA damage sites by RAD17 (Rad24 in yeast)-RLC. All five RFC complex components, but none of the three large subunits of RLC, CTF18, ATAD5, or RAD17, are essential for cell survival; however, deficiency of the three RLC proteins leads to genomic instability. In this review, we describe recent findings that contribute to the understanding of the basic roles of the RFC complex and RLCs and how genomic instability due to deficiency of the three RLCs is linked to the molecular and cellular activity of RLC, particularly focusing on ATAD5 (Elg1).

scholarly journals The Yeast PCNA Unloader Elg1 RFC-Like Complex Plays a Role in Eliciting the DNA Damage Checkpoint

mBio ◽  
2019 ◽  
Vol 10 (3) ◽  
Author(s):  
Soumitra Sau ◽  
Batia Liefshitz ◽  
Martin Kupiec
Keyword(s):  
Dna Damage ◽  
Dna Replication ◽  
Cellular Response ◽  
Genome Stability ◽  
Adaptor Proteins ◽  
Nuclear Antigen ◽  
Dna Damage Checkpoint ◽  
Activation Process ◽  
Checkpoint Activation ◽  
Dna Replication And Repair

ABSTRACT The PCNA (proliferating cell nuclear antigen) ring plays central roles during DNA replication and repair. The yeast Elg1 RFC-like complex (RLC) is the principal unloader of chromatin-bound PCNA and thus plays a central role in maintaining genome stability. Here we identify a role for Elg1 in the unloading of PCNA during DNA damage. Using DNA damage checkpoint (DC)-inducible and replication checkpoint (RC)-inducible strains, we show that Elg1 is essential for eliciting the signal in the DC branch. In the absence of Elg1 activity, the Rad9 (53BP1) and Dpb11 (TopBP1) adaptor proteins are recruited but fail to be phosphorylated by Mec1 (ATR), resulting in a lack of checkpoint activation. The chromatin immunoprecipitation of PCNA at the Lac operator sites reveals that accumulated local PCNA influences the checkpoint activation process in elg1 mutants. Our data suggest that Elg1 participates in a mechanism that may coordinate PCNA unloading during DNA repair with DNA damage checkpoint induction. IMPORTANCE The Elg1protein forms an RFC-like complex in charge of unloading PCNA from chromatin during DNA replication and repair. Mutations in the ELG1 gene caused genomic instability in all organisms tested and cancer in mammals. Here we show that Elg1 plays a role in the induction of the DNA damage checkpoint, a cellular response to DNA damage. We show that this defect is due to a defect in the signal amplification process during induction. Thus, cells coordinate the cell's response and the PCNA unloading through the activity of Elg1.

scholarly journals Requirement for the Phospho-H2AX Binding Module of Crb2 in Double-Strand Break Targeting and Checkpoint Activation

2010 ◽  
Vol 30 (19) ◽  
pp. 4722-4731 ◽  
Author(s):  
Steven L. Sanders ◽  
Ahmad R. Arida ◽  
Funita P. Phan
Keyword(s):  
Dna Damage ◽  
Histone Modification ◽  
Genome Stability ◽  
Strand Break ◽  
Binding Activity ◽  
Critical Element ◽  
Checkpoint Control ◽  
Ionizing Irradiation ◽  
Checkpoint Activation ◽  
Damage Response

ABSTRACT Activation of DNA damage checkpoints requires the rapid accumulation of numerous factors to sites of genomic lesions, and deciphering the mechanisms of this targeting is central to our understanding of DNA damage response. Histone modification has recently emerged as a critical element for the correct localization of damage response proteins, and one key player in this context is the fission yeast checkpoint mediator Crb2. Accumulation of Crb2 at ionizing irradiation-induced double-strand breaks (DSBs) requires two distinct histone marks, dimethylated H4 lysine 20 (H4K20me2) and phosphorylated H2AX (pH2AX). A tandem tudor motif in Crb2 directly binds H4K20me2, and this interaction is required for DSB targeting and checkpoint activation. Similarly, pH2AX is required for Crb2 localization to DSBs and checkpoint control. Crb2 can directly bind pH2AX through a pair of C-terminal BRCT repeats, but the functional significance of this binding has been unclear. Here we demonstrate that loss of its pH2AX-binding activity severely impairs the ability of Crb2 to accumulate at ionizing irradiation-induced DSBs, compromises checkpoint signaling, and disrupts checkpoint-mediated cell cycle arrest. These impairments are similar to that reported for abolition of pH2AX or mutation of the H4K20me2-binding tudor motif of Crb2. Intriguingly, a combined ablation of its two histone modification binding modules yields a strikingly additive reduction in Crb2 activity. These observations argue that binding of the Crb2 BRCT repeats to pH2AX is critical for checkpoint activity and provide new insight into the mechanisms of chromatin-mediated genome stability.

scholarly journals TEN1 Is Essential for CDC13-Mediated Telomere Capping

Genetics ◽  
2009 ◽  
Vol 183 (3) ◽  
pp. 793-810 ◽  
Author(s):  
Ling Xu ◽  
Ruben C. Petreaca ◽  
Hovik J. Gasparyan ◽  
Stephanie Vu ◽  
Constance I. Nugent
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Dna Replication ◽  
High Temperatures ◽  
De Novo ◽  
Temperature Sensitive ◽  
Single Stranded Dna ◽  
Growth Defects ◽  
Telomere Capping ◽  
Telomere Replication ◽  
Essential Function

Telomere binding proteins protect chromosome ends from degradation and mask chromosome termini from checkpoint surveillance. In Saccharomyces cerevisiae, Cdc13 binds single-stranded G-rich telomere repeats, maintaining telomere integrity and length. Two additional proteins, Ten1 and Stn1, interact with Cdc13 but their contributions to telomere integrity are not well defined. Ten1 is known to prevent accumulation of aberrant single-stranded telomere DNA; whether this results from defective end protection or defective telomere replication is unclear. Here we report our analysis of a new group of ten1 temperature-sensitive (ts) mutants. At permissive temperatures, ten1-ts strains display greatly elongated telomeres. After shift to nonpermissive conditions, however, ten1-ts mutants accumulate extensive telomeric single-stranded DNA. Cdk1 activity is required to generate these single-stranded regions, and deleting the EXO1 nuclease partially suppresses ten1-ts growth defects. This is similar to cdc13-1 mutants, suggesting ten1-ts strains are defective for end protection. Moreover, like Cdc13, our analysis reveals Ten1 promotes de novo telomere addition. Interestingly, in ten1-ts strains at high temperatures, telomeric single-stranded DNA and Rad52-YFP repair foci are strongly induced despite Cdc13 remaining associated with telomeres, revealing Cdc13 telomere binding is not sufficient for end protection. Finally, unlike cdc13-1 mutants, ten1-ts strains display strong synthetic interactions with mutations in the POLα complex. These results emphasize that Cdc13 relies on Ten1 to execute its essential function, but leave open the possibility that Ten1 has a Cdc13-independent role in DNA replication.

scholarly journals CDK phosphorylation of SLD-2 is required for replication initiation and germline development in C. elegans

2014 ◽  
Vol 204 (4) ◽  
pp. 507-522 ◽  
Author(s):  
Vincent Gaggioli ◽  
Eva Zeiser ◽  
David Rivers ◽  
Charles R. Bradshaw ◽  
Julie Ahringer ◽  
...  
Keyword(s):  
Vital Role ◽  
Replication Initiation ◽  
Cyclin Dependent Kinase ◽  
Germline Development ◽  
Nuclear Retention ◽  
C Elegans ◽  
Essential Function ◽  
Cdk Phosphorylation ◽  
Nematode Worm

Cyclin-dependent kinase (CDK) plays a vital role in proliferation control across eukaryotes. Despite this, how CDK mediates cell cycle and developmental transitions in metazoa is poorly understood. In this paper, we identify orthologues of Sld2, a CDK target that is important for DNA replication in yeast, and characterize SLD-2 in the nematode worm Caenorhabditis elegans. We demonstrate that SLD-2 is required for replication initiation and the nuclear retention of a critical component of the replicative helicase CDC-45 in embryos. SLD-2 is a CDK target in vivo, and phosphorylation regulates the interaction with another replication factor, MUS-101. By mutation of the CDK sites in sld-2, we show that CDK phosphorylation of SLD-2 is essential in C. elegans. Finally, using a phosphomimicking sld-2 mutant, we demonstrate that timely CDK phosphorylation of SLD-2 is an important control mechanism to allow normal proliferation in the germline. These results determine an essential function of CDK in metazoa and identify a developmental role for regulated SLD-2 phosphorylation.

scholarly journals The Drosophila telomere-capping protein Verrocchio binds single-stranded DNA and protects telomeres from DNA damage response

2016 ◽  
Vol 45 (6) ◽  
pp. 3068-3085 ◽  
Author(s):  
Alessandro Cicconi ◽  
Emanuela Micheli ◽  
Fiammetta Vernì ◽  
Alison Jackson ◽  
Ana Citlali Gradilla ◽  
...  
Keyword(s):  
Dna Damage ◽  
Dna Damage Response ◽  
Single Stranded Dna ◽  
Capping Protein ◽  
Damage Response ◽  
Telomere Capping

scholarly journals Loss of Cdc13 causes genome instability by a deficiency in replication-dependent telomere capping

2019 ◽  
Author(s):  
Rachel E Langston ◽  
Dominic Palazzola ◽  
Erin Bonnell ◽  
Raymund J. Wellinger ◽  
Ted Weinert
Keyword(s):  
Homologous Recombination ◽  
Genome Stability ◽  
Genome Instability ◽  
Chromosome Instability ◽  
S Phase ◽  
Temperature Sensitive ◽  
End Joining ◽  
Telomere Capping ◽  
Non Homologous End Joining

AbstractIn budding yeast, Cdc13, Stn1, and Ten1 form a telomere binding heterotrimer dubbed CST. Here we investigate the role of Cdc13/CST in maintaining genome stability, using a Chr VII disome system that can generate recombinants, loss, and enigmatic unstable chromosomes. In cells expressing a temperature sensitive CDC13 allele, cdc13F684S, unstable chromosomes frequently arise due to problems in or near a telomere. Hence, when Cdc13 is defective, passage through S phase causes Exo1-dependent ssDNA and unstable chromosomes, which then are the source for whole chromosome instability events (e.g. recombinants, chromosome truncations, dicentrics, and/or loss). Specifically, genome instability arises from a defect in Cdc13’s replication-dependent telomere capping function, not Cdc13s putative post-replication telomere capping function. Furthermore, the unstable chromosomes form without involvement of homologous recombination nor non-homologous end joining. Our data suggest that a Cdc13/CST defect in semi-conservative replication near the telomere leads to ssDNA and unstable chromosomes, which then are lost or subject to complex rearrangements. This system defines a links between replication-dependent chromosome capping and genome stability in the form of unstable chromosomes.

scholarly journals The zinc-finger transcription factor LSL-1 is a major regulator of the germline transcriptional program in C. elegans

2021 ◽  
Author(s):  
David Rodriguez-Crespo ◽  
Magali Nanchen ◽  
Shweta Rajopadhye ◽  
Chantal Wicky
Keyword(s):  
Meiotic Prophase ◽  
Genome Stability ◽  
Primordial Germ Cell ◽  
Somatic Cells ◽  
Specific Gene ◽  
Loss Of Function ◽  
Transcriptional Program ◽  
Germline Development ◽  
C Elegans ◽  
Germline Genes

Specific gene transcriptional programs are required to ensure proper proliferation and differentiation processes underlying the production of specialized cells during development. Gene activity is mainly regulated by the concerted action of transcription factors and chromatin proteins. In the nematode C. elegans, mechanisms that silence improper transcriptional programs in germline and somatic cells have been well studied, however, how are tissue specific sets of genes turned on is less known. LSL-1 is herein defined as a novel crucial transcriptional regulator of germline genes in C. elegans. LSL-1 is first detected in the P4 blastomere and remains present at all stages of germline development, from primordial germ cell proliferation to the end of meiotic prophase. lsl-1 loss-of-function mutants exhibit many defects including meiotic prophase progression delay, a high level of germline apoptosis, and production of almost no functional gametes. Transcriptomic analysis and ChIP-seq data show that LSL-1 binds to promoters and acts as a transcriptional activator of germline genes involved in various processes, including homologous chromosome pairing, recombination, and genome stability. Furthermore, we show that LSL-1 functions by antagonizing the action of the heterochromatin proteins HPL-2/HP1 and LET-418/Mi2 known to be involved in the repression of germline genes in somatic cells. Based on our results, we propose LSL-1 to be a major regulator of the germline transcriptional program during development.

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