NHK-1 phosphorylates BAF to allow karyosome formation in the Drosophila oocyte nucleus

Accurate chromosome segregation in meiosis requires dynamic changes in chromatin organization. In Drosophila melanogaster, upon completion of recombination, meiotic chromosomes form a single, compact cluster called the karyosome in an enlarged oocyte nucleus. This clustering is also found in humans; however, the mechanisms underlying karyosome formation are not understood. In this study, we report that phosphorylation of barrier to autointegration factor (BAF) by the conserved kinase nucleosomal histone kinase-1 (NHK-1; Drosophila Vrk1) has a critical function in karyosome formation. We find that the noncatalytic domain of NHK-1 is crucial for its kinase activity toward BAF, a protein that acts as a linker between chromatin and the nuclear envelope. A reduction of NHK-1 or expression of nonphosphorylatable BAF results in ectopic association of chromosomes with the nuclear envelope in oocytes. We propose that BAF phosphorylation by NHK-1 disrupts anchorage of chromosomes to the nuclear envelope, allowing karyosome formation in oocytes. These data provide the first mechanistic insight into how the karyosome forms.     

A maternal screen for genes regulating Drosophila oocyte polarity uncovers new steps in meiotic progression

Meiotic checkpoints monitor chromosome status to ensure correct homologous recombination, genomic integrity, and chromosome segregation. In Drosophila, the persistent presence of double-strand DNA breaks (DSB) activates the ATR/Mei-41 checkpoint, delays progression through meiosis, and causes defects in DNA condensation of the oocyte nucleus, the karyosome. Checkpoint activation has also been linked to decreased levels of the TGFalpha-like molecule Gurken, which controls normal eggshell patterning. We used this easy-to-score eggshell phenotype in a germ-line mosaic screen in Drosophila to identify new genes affecting meiotic progression, DNA condensation, and Gurken signaling. One hundred eighteen new ventralizing mutants on the second chromosome fell into 17 complementation groups. Here we describe the analysis of 8 complementation groups, including Kinesin heavy chain, the SR protein kinase cuaba, the cohesin-related gene dPds5/cohiba, and the Tudor-domain gene montecristo. Our findings challenge the hypothesis that checkpoint activation upon persistent DSBs is exclusively mediated by ATR/Mei-41 kinase and instead reveal a more complex network of interactions that link DSB formation, checkpoint activation, meiotic delay, DNA condensation, and Gurken protein synthesis.     

Activation of a meiotic checkpoint during Drosophila oogenesis regulates the translation of Gurken through Chk2/Mnk

BACKGROUND: During Drosophila oogenesis, unrepaired double-strand DNA breaks activate a mei-41-dependent meiotic checkpoint, which couples the progression through meiosis to specific developmental processes. This checkpoint affects the accumulation of Gurken protein, a transforming growth factor alpha-like signaling molecule, as well as the morphology of the oocyte nucleus. However, the components of this checkpoint in flies have not been completely elucidated. RESULTS: We show that a mutation in the Drosophila Chk2 homolog (DmChk2/Mnk) suppresses the defects in the translation of gurken mRNA and also the defects in oocyte nuclear morphology. We also found that DmChk2 is phosphorylated in a mei-41-dependent pathway. Analysis of the meiotic cell cycle progression shows that the Drosophila Chk2 homolog is not required during early meiotic prophase, as has been observed for Chk2 in C. elegans. We demonstrate that the activation of the meiotic checkpoint affects Dwee1 localization and is associated with DmChk2-dependent posttranslational modification of Dwee1. We suggest that Dwee1 has a role in the meiotic checkpoint that regulates the meiotic cell cycle, but not the translation of gurken mRNA. In addition, we found that p53 and mus304, the Drosophila ATR-IP homolog, are not required for the patterning defects caused by the meiotic DNA repair mutations. CONCLUSIONS: DmChk2 is a transducer of the meiotic checkpoint in flies that is activated by unrepaired double-strand DNA breaks. Activation of DmChk2 in this specific checkpoint affects a cell cycle regulator as well as mRNA translation.     

Essential and Checkpoint Functions of Budding Yeast ATM and ATR during Meiotic Prophase Are Facilitated by Differential Phosphorylation of a Meiotic Adaptor Protein,Hop1

A hallmark of the conserved ATM/ATR signalling is its ability to mediate a wide range of functions utilizing only a limited number of adaptors and effector kinases. During meiosis, Tel1 and Mec1, the budding yeast ATM and ATR, respectively, rely on a meiotic adaptor protein Hop1, a 53BP1/Rad9 functional analog, and its associated kinase Mek1, a CHK2/Rad53-paralog, to mediate multiple functions: control of the formation and repair of programmed meiotic DNA double strand breaks, enforcement of inter-homolog bias, regulation of meiotic progression, and implementation of checkpoint responses. Here, we present evidence that the multi-functionality of the Tel1/Mec1-to-Hop1/Mek1 signalling depends on stepwise activation of Mek1 that is mediated by Tel1/Mec1 phosphorylation of two specific residues within Hop1: phosphorylation at the threonine 318 (T318) ensures the transient basal level Mek1 activation required for viable spore formation during unperturbed meiosis. Phosphorylation at the serine 298 (S298) promotes stable Hop1-Mek1 interaction on chromosomes following the initial phospho-T318 mediated Mek1 recruitment. In the absence of Dmc1, the phospho-S298 also promotes Mek1 hyper-activation necessary for implementing meiotic checkpoint arrest. Taking these observations together, we propose that the Hop1 phospho-T318 and phospho-S298 constitute key components of the Tel1/Mec1- based meiotic recombination surveillance (MRS) network and facilitate effective coupling of meiotic recombination and progression during both unperturbed and challenged meiosis.     

TopBP1 and ATR colocalization at meiotic chromosomes: role of TopBP1/Cut5 in the meiotic recombination checkpoint

Mammalian TopBP1 is a BRCT domain-containing protein whose function in mitotic cells is linked to replication and DNA damage checkpoint. Here, we study its possible role during meiosis in mice. TopBP1 foci are abundant during early prophase I and localize mainly to histone gamma-H2AX-positive domains, where DNA double-strand breaks (required to initiate recombination) occur. Strikingly, TopBP1 showed a pattern almost identical to that of ATR, a PI3K-like kinase involved in mitotic DNA damage checkpoint. In the synapsis-defective Fkbp6(-/-) mouse, TopBP1 heavily stains unsynapsed regions of chromosomes. We also tested whether Schizosaccharomyces pombe Cut5 (the TopBP1 homologue) plays a role in the meiotic recombination checkpoint, like spRad3, the ATR homologue. Indeed, we found that a cut5 mutation suppresses the checkpoint-dependent meiotic delay of a meiotic recombination defective mutant, indicating a direct role of the Cut5 protein in the meiotic checkpoint. Our findings suggest that ATR and TopBP1 monitor meiotic recombination and are required for activation of the meiotic recombination checkpoint.     

Dot1-Dependent Histone H3K79 Methylation Promotes Activation of the Mek1 Meiotic Checkpoint Effector Kinase by Regulating the Hop1 Adaptor

During meiosis, accurate chromosome segregation relies on the proper interaction between homologous chromosomes, including synapsis and recombination. The meiotic recombination checkpoint is a quality control mechanism that monitors those crucial events. In response to defects in synapsis and/or recombination, this checkpoint blocks or delays progression of meiosis, preventing the formation of aberrant gametes. Meiotic recombination occurs in the context of chromatin and histone modifications, which play crucial roles in the maintenance of genomic integrity. Here, we unveil the role of Dot1-dependent histone H3 methylation at lysine 79 (H3K79me) in this meiotic surveillance mechanism. We demonstrate that the meiotic checkpoint function of Dot1 relies on H3K79me because, like the dot1 deletion, H3-K79A or H3-K79R mutations suppress the checkpoint-imposed meiotic delay of a synapsis-defective zip1 mutant. Moreover, by genetically manipulating Dot1 catalytic activity, we find that the status of H3K79me modulates the meiotic checkpoint response. We also define the phosphorylation events involving activation of the meiotic checkpoint effector Mek1 kinase. Dot1 is required for Mek1 autophosphorylation, but not for its Mec1/Tel1-dependent phosphorylation. Dot1-dependent H3K79me also promotes Hop1 activation and its proper distribution along zip1 meiotic chromosomes, at least in part, by regulating Pch2 localization. Furthermore, HOP1 overexpression bypasses the Dot1 requirement for checkpoint activation. We propose that chromatin remodeling resulting from unrepaired meiotic DSBs and/or faulty interhomolog interactions allows Dot1-mediated H3K79-me to exclude Pch2 from the chromosomes, thus driving localization of Hop1 along chromosome axes and enabling Mek1 full activation to trigger downstream responses, such as meiotic arrest.     

Drosophila brca2 is required for mitotic and meiotic DNA repair and efficient activation of the meiotic recombination checkpoint

Heterozygous mutations in the tumor suppressor BRCA2 confer a high risk of breast and other cancers in humans. BRCA2 maintains genome stability in part through the regulation of Rad51-dependent homologous recombination. Much about its precise function in the DNA damage responses is, however, not yet known. We have made null mutations in the Drosophila homolog of BRCA2 and measured the levels of homologous recombination, non-homologous end-joining, and single-strand annealing in the pre-meiotic germline of Drosophila males. We show that repair by homologous recombination is dramatically decreased in Drosophila brca2 mutants. Instead, large flanking deletions are formed, and repair by the non-conservative single-strand annealing pathway predominates. We further show that during meiosis, Drosophila Brca2 has a dual role in the repair of meiotic double-stranded breaks and the efficient activation of the meiotic recombination checkpoint. The eggshell patterning defects that result from activation of the meiotic recombination checkpoint in other meiotic DNA repair mutants can be strongly suppressed by mutations in brca2. In addition, Brca2 co-immunoprecipitates with the checkpoint protein Rad9, suggesting a direct role for Brca2 in the transduction of the meiotic recombination checkpoint signal.     

Direct and Indirect Control of the Initiation of Meiotic Recombination by DNA Damage Checkpoint Mechanisms in Budding Yeast

Meiotic recombination plays an essential role in the proper segregation of chromosomes at meiosis I in many sexually reproducing organisms. Meiotic recombination is initiated by the scheduled formation of genome-wide DNA double-strand breaks (DSBs). The timing of DSB formation is strictly controlled because unscheduled DSB formation is detrimental to genome integrity. Here, we investigated the role of DNA damage checkpoint mechanisms in the control of meiotic DSB formation using budding yeast. By using recombination defective mutants in which meiotic DSBs are not repaired, the effect of DNA damage checkpoint mutations on DSB formation was evaluated. The Tel1 (ATM) pathway mainly responds to unresected DSB ends, thus the sae2 mutant background in which DSB ends remain intact was employed. On the other hand, the Mec1 (ATR) pathway is primarily used when DSB ends are resected, thus the rad51 dmc1 double mutant background was employed in which highly resected DSBs accumulate. In order to separate the effect caused by unscheduled cell cycle progression, which is often associated with DNA damage checkpoint defects, we also employed the ndt80 mutation which permanently arrests the meiotic cell cycle at prophase I. In the absence of Tel1, DSB formation was reduced in larger chromosomes (IV, VII, II and XI) whereas no significant reduction was found in smaller chromosomes (III and VI). On the other hand, the absence of Rad17 (a critical component of the ATR pathway) lead to an increase in DSB formation (chromosomes VII and II were tested). We propose that, within prophase I, the Tel1 pathway facilitates DSB formation, especially in bigger chromosomes, while the Mec1 pathway negatively regulates DSB formation. We also identified prophase I exit, which is under the control of the DNA damage checkpoint machinery, to be a critical event associated with down-regulating meiotic DSB formation.     

Drosophila PCH2 is required for a pachytene checkpoint that monitors double-strand-break-independent events leading to meiotic crossover formation

During meiosis, programmed DNA double-strand breaks (DSBs) are repaired to create at least one crossover per chromosome arm. Crossovers mature into chiasmata, which hold and orient the homologous chromosomes on the meiotic spindle to ensure proper segregation at meiosis I. This process is usually monitored by one or more checkpoints that ensure that DSBs are repaired prior to the meiotic divisions. We show here that mutations in Drosophila genes required to process DSBs into crossovers delay two important steps in meiotic progression: a chromatin-remodeling process associated with DSB formation and the final steps of oocyte selection. Consistent with the hypothesis that a checkpoint has been activated, the delays in meiotic progression are suppressed by a mutation in the Drosophila homolog of pch2. The PCH2-dependent delays also require proteins thought to regulate the number and distribution of crossovers, suggesting that this checkpoint monitors events leading to crossover formation. Surprisingly, two lines of evidence suggest that the PCH2-dependent checkpoint does not reflect the accumulation of unprocessed recombination intermediates: the delays in meiotic progression do not depend on DSB formation or on mei-41, the Drosophila ATR homolog, which is required for the checkpoint response to unrepaired DSBs. We propose that the sites and/or conditions required to promote crossovers are established independently of DSB formation early in meiotic prophase. Furthermore, the PCH2-dependent checkpoint is activated by these events and pachytene progression is delayed until the DSB repair complexes required to generate crossovers are assembled. Interestingly, PCH2-dependent delays in prophase may allow additional crossovers to form.     

Replication protein A is sequentially phosphorylated during meiosis

Phosphorylation of the cellular single-stranded DNA-binding protein, replication protein A (RPA), occurs during normal mitotic cell cycle progression and also in response to genotoxic stress. In budding yeast, these reactions require the ATM homolog Mec1, a central regulator of the DNA replication and DNA damage checkpoint responses. We now demonstrate that the middle subunit of yeast RPA (Rfa2) becomes phosphorylated in two discrete steps during meiosis. Primary Rfa2 phosphorylation occurs early in meiotic progression and is independent of DNA replication, recombination and Mec1. In contrast, secondary Rfa2 phosphorylation is activated upon initiation of recombination and requires Mec1. While the primary Rfa2 phosphoisomer is detectable throughout most of meiosis, the secondary Rfa2 phosphoisomer is only transiently generated and begins to disappear soon after recombination is complete. Extensive secondary Rfa2 phosphorylation is observed in a recombination mutant defective for the pachytene checkpoint, indicating that Mec1-dependent Rfa2 phosphorylation does not function to maintain meiotic delay in response to DNA double-strand breaks. Our results suggest that Mec1-dependent RPA phosphorylation could be involved in regulating recombination rather than cell cycle or meiotic progression.     

Surveillance mechanisms monitoring chromosome breaks during mitosis and meiosis

DNA double-strand breaks (DSBs) are highly hazardous for genome integrity, because failure to repair them can lead to genome rearrangements or chromosome loss. They can arise at unpredictable locations as a consequence of DNA damage during both the mitotic and the meiotic cell cycle or in a programmed manner during meiosis. Cellular response to accidental or programmed DSBs involves highly conserved surveillance mechanisms, called DNA damage checkpoint and recombination checkpoint, which coordinate DSB repair with mitotic or meiotic cell cycle progression, respectively. Although these protective signal-transduction pathways share several upstream components, activation of the recombination checkpoint requires meiosis-specific proteins. These proteins are structural components of the meiotic chromosomes, indicating that the system monitoring programmed meiotic DSBs is an integral part of the chromosome structure formed during meiosis.     

The cell-cycle checkpoint kinase Chk1 is required for mammalian homologous recombination repair

The essential checkpoint kinase Chk1 is required for cell-cycle delays after DNA damage or blocked DNA replication. However, it is unclear whether Chk1 is involved in the repair of damaged DNA. Here we establish that Chk1 is a key regulator of genome maintenance by the homologous recombination repair (HRR) system. Abrogation of Chk1 function with small interfering RNA or chemical antagonists inhibits HRR, leading to persistent unrepaired DNA double-strand breaks (DSBs) and cell death after replication inhibition with hydroxyurea or DNA-damage caused by camptothecin. After hydroxyurea treatment, the essential recombination repair protein RAD51 is recruited to DNA repair foci performing a vital role in correct HRR. We demonstrate that Chk1 interacts with RAD51, and that RAD51 is phosphorylated on Thr 309 in a Chk1-dependent manner. Consistent with a functional interplay between Chk1 and RAD51, Chk1-depleted cells failed to form RAD51 nuclear foci after exposure to hydroxyurea, and cells expressing a phosphorylation-deficient mutant RAD51(T309A) were hypersensitive to hydroxyurea. These results highlight a crucial role for the Chk1 signalling pathway in protecting cells against lethal DNA lesions through regulation of HRR.     

Pachytene exit controlled by reversal of Mek1-dependent phosphorylation

During yeast meiosis, a checkpoint prevents exit from pachytene in response to defects in meiotic recombination and chromosome synapsis. This pachytene checkpoint requires two meiotic chromosomal proteins, Red1 and Mek1; Mek1 is a kinase that phosphorylates Red1. In mutants that undergo checkpoint-mediated pachytene arrest, Mek1 is active and Red1 remains phosphorylated. Activation of Mek1 requires the initiation of meiotic recombination and certain DNA damage checkpoint proteins. Mek1 kinase activity and checkpoint-induced pachytene arrest are counteracted by protein phosphatase type 1 (Glc7). Glc7 coimmunoprecipitates with Red1, colocalizes with Red1 on chromosomes, and dephosphorylates Red1 in vitro. We speculate that phosphorylated Red1 prevents exit from pachytene and that completion of meiotic recombination triggers Glc7-dependent dephosphorylation of Red1.     

Matefin/SUN-1 Phosphorylation Is Part of a Surveillance Mechanism to Coordinate Chromosome Synapsis and Recombination with Meiotic Progression and Chromosome Movement

Faithful chromosome segregation during meiosis I depends on the establishment of a crossover between homologous chromosomes. This requires induction of DNA double-strand breaks (DSBs), alignment of homologs, homolog association by synapsis, and repair of DSBs via homologous recombination. The success of these events requires coordination between chromosomal events and meiotic progression. The conserved SUN/KASH nuclear envelope bridge establishes transient linkages between chromosome ends and cytoskeletal forces during meiosis. In Caenorhabditis elegans, this bridge is essential for bringing homologs together and preventing nonhomologous synapsis. Chromosome movement takes place during synapsis and recombination. Concomitant with the onset of chromosome movement, SUN-1 clusters at chromosome ends associated with the nuclear envelope, and it is phosphorylated in a chk-2- and plk-2-dependent manner. Identification of all SUN-1 phosphomodifications at its nuclear N terminus allowed us to address their role in prophase I. Failures in recombination and synapsis led to persistent phosphorylations, which are required to elicit a delay in progression. Unfinished meiotic tasks elicited sustained recruitment of PLK-2 to chromosome ends in a SUN-1 phosphorylation–dependent manner that is required for continued chromosome movement and characteristic of a zygotene arrest. Furthermore, SUN-1 phosphorylation supported efficient synapsis. We propose that signals emanating from a failure to successfully finish meiotic tasks are integrated at the nuclear periphery to regulate chromosome end–led movement and meiotic progression. The single unsynapsed X chromosome in male meiosis is precluded from inducing a progression delay, and we found it was devoid of a population of phosphorylated SUN-1. This suggests that SUN-1 phosphorylation is critical to delaying meiosis in response to perturbed synapsis. SUN-1 may be an integral part of a checkpoint system to monitor establishment of the obligate crossover, inducible only in leptotene/zygotene. Unrepaired DSBs and unsynapsed chromosomes maintain this checkpoint, but a crossover intermediate is necessary to shut it down.     

DNA double-strand breaks in meiosis: Checking their formation, processing and repair

DNA double-strand breaks (DSBs) are highly hazardous for genome integrity, but meiotic cells deliberately introduce them into their genome in order to initiate homologous recombination, which ensures proper homologous chromosome segregation. To minimize the risk of deleterious effects, meiotic DSB formation, processing and repair are tightly regulated in order to occur only at the right time and place. Furthermore, a highly conserved signal-transduction pathway, called meiotic recombination checkpoint, coordinates DSB repair with meiotic progression and promotes meiotic recombination.     

Drosophila mus301/spindle-C encodes a helicase with an essential role in double-strand DNA break repair and meiotic progression

mus301 was identified independently in two genetic screens, one for mutants hypersensitive to chemical mutagens and another for maternal mutants with eggshell defects. mus301 is required for the proper specification of the oocyte and for progression through meiosis in the Drosophila ovary. We have cloned mus301 and show that it is a member of the Mus308 subfamily of ATP-dependent helicases and the closest homolog of human and mouse HEL308. Functional analyses demonstrate that Mus301 is involved in chromosome segregation in meiosis and in the repair of double-strand-DNA breaks in both meiotic and mitotic cells. Most of the oogenesis defects of mus301 mutants are suppressed by mutants in the checkpoint kinase Mei41 and in MeiW68, the Spo11 homolog that is thought to generate the dsDNA breaks that initiate recombination, indicating that these phenotypes are caused by activation of the DNA damage checkpoint in response to unrepaired Mei-W68-induced dsDNA breaks. However, neither mei-W68 nor mei-41 rescue the defects in oocyte specification of mus301 mutants, suggesting that this helicase has another function in oocyte selection that is independent from its role in meiotic recombination.     

AtSPO11-1 is necessary for efficient meiotic recombination in plants

The Saccharomyces cerevisiae Spo11 protein catalyses DNA double-strand breaks (DSBs) that initiate meiotic recombination. The model plant Arabidopsis thaliana possesses at least three SPO11 homologues. T-DNA and ethyl-methane sulfonate mutagenesis allowed us to show that meiotic progression is altered in plants in which the AtSPO11-1 gene is disrupted. Both male and female meiocytes formed very few bivalents. Furthermore, no fully synapsed chromosomes were observed during prophase I. Later, in meiosis I, we observed that chromosomes segregated randomly, leading to the production of a large proportion of non-functional gametes. These meiotic aberrations were associated with a drastic reduction in meiotic recombination. Thus, our data show that initiation of meiotic recombination by SPO11- induced DSBs is a mechanism conserved in plants. Furthermore, unlike Drosophila and Caenorhabditis elegans, but like fungi, SPO11 is necessary for normal synapsis in plants.     

The Drosophila Meiotic Recombination Gene Mei-9 Encodes a Homologue of the Yeast Excision Repair Protein Rad1

Meiotic recombination and DNA repair are mediated by overlapping sets of genes. In the yeast Saccharomyces cerevisiae, many genes required to repair DNA double-strand breaks are also required for meiotic recombination. In contrast, mutations in genes required for nucleotide excision repair (NER) have no detectable effects on meiotic recombination in S. cerevisiae. The Drosophila melanogaster mei-9 gene is unique among known recombination genes in that it is required for both meiotic recombination and NER. We have analyzed the mei-9 gene at the molecular level and found that it encodes a homologue of the S. cerevisiae excision repair protein Rad1, the probable homologue of mammalian XPF/ERCC4. Hence, the predominant process of meiotic recombination in Drosophila proceeds through a pathway that is at least partially distinct from that of S. cerevisiae, in that it requires an NER protein. The biochemical properties of the Rad1 protein allow us to explain the observation that mei-9 mutants suppress reciprocal exchange without suppressing the frequency of gene conversion.     

Role of the Saccharomyces cerevisiae Rad53 checkpoint kinase in signaling double-strand breaks during the meiotic cell cycle

DNA double-strand breaks (DSBs) can arise at unpredictable locations after DNA damage or in a programmed manner during meiosis. DNA damage checkpoint response to accidental DSBs during mitosis requires the Rad53 effector kinase, whereas the meiosis-specific Mek1 kinase, together with Red1 and Hop1, mediates the recombination checkpoint in response to programmed meiotic DSBs. Here we provide evidence that exogenous DSBs lead to Rad53 phosphorylation during the meiotic cell cycle, whereas programmed meiotic DSBs do not. However, the latter can trigger phosphorylation of a protein fusion between Rad53 and the Mec1-interacting protein Ddc2, suggesting that the inability of Rad53 to transduce the meiosis-specific DSB signals might be due to its failure to access the meiotic recombination sites. Rad53 phosphorylation/activation is elicited when unrepaired meiosis-specific DSBs escape the recombination checkpoint. This activation requires homologous chromosome segregation and delays the second meiotic division. Altogether, these data indicate that Rad53 prevents sister chromatid segregation in the presence of unrepaired programmed meiotic DSBs, thus providing a salvage mechanism ensuring genetic integrity in the gametes even in the absence of the recombination checkpoint.     

ZTF-8 Interacts with the 9-1-1 Complex and Is Required for DNA Damage Response and Double-Strand Break Repair in the C. elegans Germline

Germline mutations in DNA repair genes are linked to tumor progression. Furthermore, failure in either activating a DNA damage checkpoint or repairing programmed meiotic double-strand breaks (DSBs) can impair chromosome segregation. Therefore, understanding the molecular basis for DNA damage response (DDR) and DSB repair (DSBR) within the germline is highly important. Here we define ZTF-8, a previously uncharacterized protein conserved from worms to humans, as a novel factor involved in the repair of both mitotic and meiotic DSBs as well as in meiotic DNA damage checkpoint activation in the C. elegans germline. ztf-8 mutants exhibit specific sensitivity to γ-irradiation and hydroxyurea, mitotic nuclear arrest at S-phase accompanied by activation of the ATL-1 and CHK-1 DNA damage checkpoint kinases, as well as accumulation of both mitotic and meiotic recombination intermediates, indicating that ZTF-8 functions in DSBR. However, impaired meiotic DSBR progression partially fails to trigger the CEP-1/p53-dependent DNA damage checkpoint in late pachytene, also supporting a role for ZTF-8 in meiotic DDR. ZTF-8 partially co-localizes with the 9-1-1 DDR complex and interacts with MRT-2/Rad1, a component of this complex. The human RHINO protein rescues the phenotypes observed in ztf-8 mutants, suggesting functional conservation across species. We propose that ZTF-8 is involved in promoting repair at stalled replication forks and meiotic DSBs by transducing DNA damage checkpoint signaling via the 9-1-1 pathway. Our findings define a conserved function for ZTF-8/RHINO in promoting genomic stability in the germline.