Biology subjects

Dernburg, A. F.

Publications and source records attributed to Dernburg, A. F..

10 recordsLinked to original sources

bioRxiv2026

NPP-21/TPR is required for developmental control of spindle checkpoint strength in C. elegans

The spindle checkpoint ensures accurate chromosome segregation by monitoring whether chromosomes, via kinetochores, are properly attached to the spindle. If chromosomes fail to establish bipolar attachment, the checkpoint delays the cell cycle to enable error correction. In C. elegans early embryos, activation of the spindle checkpoint produces a longer mitotic delay in primordial germ cells than somatic cells. We show that the conserved nucleoporin and spindle matrix component, NPP-21/TPR, is required for the stronger spindle checkpoint in germline cells. A checkpoint-proficient NPP-21::GFP transgene localizes to a spindle-like structure during mitosis and is enriched in germline cells, consistent with a cell-fate specific function for this protein. Finally, NPP-21 controls spindle checkpoint strength in germline cells via two, potentially linked, mechanisms: concentrating PCH-2 around mitotic chromosomes and promoting the localization of the checkpoint effector, Mad2, to unattached kinetochores. These experiments demonstrate a developmental role for NPP-21, and the spindle matrix, in controlling spindle checkpoint strength in immortal germline cells in C. elegans.

cell biology↗

bioRxiv2023

Chemically induced proximity reveals mechanotransduction of a meiotic checkpoint at the nuclear envelope

Successful sexual reproduction relies on robust quality control during meiosis. Assembly of the synaptonemal complex between homologous chromosomes (synapsis) regulates meiotic recombination and is crucial for accurate chromosome segregation in most eukaryotes. Synapsis defects can trigger cell cycle delays and, in some cases, apoptosis. Here, by developing and deploying a new chemically induced proximity system, we iden-tify key players in this quality control pathway in Caenorhabditis elegans. We find that persistence of the Polo-like kinase PLK-2 at pairing centers, specialized chromosome regions that interact with the nuclear envelope to promote homolog pairing and synapsis, induces apoptosis of oocytes by phosphorylating and destabilizing the nuclear lamina. Unexpectedly, we find that a mechanosensitive Piezo1/PEZO-1 channel localizes to the nuclear envelope and is required to transduce this signal to promote apoptosis. Thus, mechanosensitive ion channels play essential roles in detecting nuclear events and triggering apoptosis during gamete production. One-sentence summaryDestabilization of the nuclear lamina triggers Piezo-dependent germline apoptosis.

cell biology↗

bioRxiv2022

A novel meiotic protein required for homolog pairing and regulation of synapsis in C. elegans

Interactions between chromosomes and LINC (Linker of Nucleoskeleton and Cytoskeleton) complexes in the nuclear envelope (NE) promote homolog pairing and synapsis during meiosis. By tethering chromosomes to cytoskeletal motors, these connections lead to rapid, processive chromosome movements along the NE. This activity is usually mediated by telomeres, but in the nematode Caenorhabditis elegans special chromosome regions called "Pairing Centers" (PCs) have acquired this meiotic function. Through a genetic screen for mutations that cause meiotic nondisjunction, we discovered an uncharacterized meiosis-specific NE protein, MJL-1 (MAJIN-Like-1) that is essential for interactions between PCs and LINC complexes. MJL-1 colocalizes with PCs and LINC complexes during pairing and synapsis. Mutations in MJL-1 disrupt these interactions and eliminate active chromosome movements. mjl-1 mutants display promiscuous nonhomologous synapsis, reduced clustering of PCs, and severely impaired homolog pairing. MJL-1 likely interacts directly with SUN-1 and DNA-binding proteins to connect PCs to the LINC complex. Similarities in the molecular architecture of chromosome-LINC complex attachments between C. elegans and other organisms suggest that these connections may play previously unrecognized roles during meiosis across eukaryotes.

cell biology↗

bioRxiv2022

Phosphoregulation of DSB-1 mediates control of meiotic double-strand break activity

In the first meiotic cell division, proper segregation of chromosomes in most organisms depends on chiasmata, exchanges of continuity between homologous chromosomes that originate from the repair of programmed double-strand breaks (DSBs) catalyzed by the Spo11 endonuclease. Since DSBs can lead to irreparable damage in germ cells, while chromosomes lacking DSBs also lack chiasmata, the number of DSBs must be carefully regulated, so as to be neither too high nor too low. Here, we show that in Caenorhabditis elegans, meiotic DSB levels are controlled by the phosphoregulation of DSB-1, a homolog of the yeast Spo11 cofactor Rec114, by the opposing activities of PP4PPH-4.1 phosphatase and ATRATL-1 kinase. Increased DSB-1 phosphorylation in pph-4.1 mutants correlates with reduction in DSB formation, while prevention of DSB-1 phosphorylation drastically increases the number of meiotic DSBs both in pph-4.1 mutants as well as in the wild type background. C. elegans and its close relatives also possess a diverged paralog of DSB-1, called DSB-2, and loss of dsb-2 is known to reduce DSB formation in oocytes with increasing age. We show that the proportion of the phosphorylated, and thus inactivated, form of DSB-1 increases with age and also upon loss of DSB-2, while non-phosphorylatable DSB-1 rescues the age-dependent decrease in DSBs in dsb-2 mutants. These results suggest that DSB-2 evolved in part to compensate for the inactivation of DSB-1 through phosphorylation, to maintain levels of DSBs in older animals. Our work shows that PP4PPH-4.1, ATRATL-1, and DSB-2 act in concert with DSB-1 to promote optimal DSB levels throughout the reproductive lifespan.

cell biology↗

bioRxiv2022

Robust, versatile DNA FISH probes for chromosome-specific repeats in Caenorhabditis elegans and Pristionchus pacificus

Repetitive DNA sequences are useful targets for chromosomal fluorescence in situ hybridization (FISH). We analyzed recent genome assemblies of Caenorhabditis elegans and Pristionchus pacificus to identify tandem repeats with a unique genomic localization. Based on these findings, we designed and validated sets of oligonucleotide probes for each species targeting at least one locus per chromosome. These probes yielded reliable fluorescent signals in different tissues and can easily be combined with immunolocalization of cellular proteins. Synthesis and labeling of these probes are highly cost-effective and require no hands-on labor. The methods presented here can be easily applied in other model and non-model organisms with a sequenced genome.

cell biology↗

bioRxiv2021

DNA damage signaling regulates cohesin stabilization and promotes meiotic chromosome axis morphogenesis

A hallmark of meiosis is the reorganization of chromosomes as linear arrays of chromatin loops around a chromosome axis comprised of cohesins and regulatory proteins. Defective axis morphogenesis impairs homolog pairing, synapsis, and recombination. We find that axis assembly in C. elegans is promoted by DNA Damage Response (DDR) signaling activated at meiotic entry. Central to this regulation is downregulation of the cohesin release factor WAPL-1 by the DDR transducer kinase ATM-1, which is activated by the meiotic kinase CHK-2. Additional cohesin regulators, including ECO-1 and PDS-5, also contribute to stabilizing axis-associated cohesins. We find that downregulation of WAPL by ATM also promotes cohesin enrichment at DNA damage foci in cultured mammalian cells. Our findings reveal that the DDR and Wapl play conserved roles in cohesin regulation in meiotic prophase and proliferating cells. One-Sentence SummaryDNA Damage Response kinase ATM phosphorylates WAPL to promote meiotic chromosome axis assembly and DNA repair

cell biology↗

bioRxiv2021

A cooperative network at the nuclear envelope counteracts LINC-mediated forces during oogenesis in C. elegans

Oogenesis involves meiosis and oocyte maturation. Both processes rely on mechanical forces (Lee et al., 2015; Nagamatsu et al., 2019; Rog and Dernburg, 2015; Sato et al., 2009; Tsatskis et al., 2020; Wynne et al., 2012), which can be transduced from the cytoskeleton to the nuclear envelope (NE) through linker of nucleoskeleton and cytoskeleton (LINC) complexes (Burke, 2018; Chang et al., 2015; Fan et al., 2020; Link et al., 2014). Gametes must protect their genomes from damage in this mechanically stressful environment. In C. elegans, oocyte nuclei lacking the single lamin protein LMN-1 are vulnerable to nuclear collapse. Here we deploy the auxin-inducible degradation system to investigate the balance of forces that drive this collapse and protect oocyte nuclei. We find that nuclear collapse is not a consequence of apoptosis. It is promoted by dynein and a LINC complex comprised of SUN-1 and ZYG-12, which assumes polarized distribution at the NE in response to dynein-mediated forces. We also show that the lamin meshwork works in parallel with other inner nuclear membrane (INM) proteins to counteract mechanical stress at the NE during oogenesis. We speculate that a similar network may protect oocyte integrity during the long arrest period in mammals.

cell biology↗

bioRxiv2021

Meiotic cell cycle progression requires adaptation to a constitutive DNA damage signal

Meiotic chromosome segregation relies on synapsis and crossover recombination between homologous chromosomes. These processes require multiple steps that are coordinated by the meiotic cell cycle and monitored by surveillance mechanisms. In diverse species, failures in chromosome synapsis can trigger a cell cycle delay and/or lead to apoptosis. How this key step in "homolog engagement" is sensed and transduced by meiotic cells is unknown. Here we report that in C. elegans, recruitment of the Polo-like kinase PLK-2 to the synaptonemal complex triggers phosphorylation and inactivation of CHK-2, an early meiotic kinase required for pairing, synapsis, and double-strand break induction. Inactivation of CHK-2 ends double-strand break formation and promotes crossover designation and cell cycle progression. These findings illuminate how meiotic cells ensure crossover formation and accurate chromosome segregation. SummaryAccurate chromosome segregation during meiosis requires crossovers between each pair of homologs. Zhang et al. show that meiotic progression in C. elegans involves inactivation of CHK-2 by PLK-2 in response to synapsis and formation of crossover precursors on all chromosomes.

cell biology↗

bioRxiv2017

A compartmentalized, self-extinguishing signaling network mediates crossover control in meiosis

Meiotic recombination between homologous chromosomes is tightly regulated to ensure proper chromosome segregation. Each chromosome pair typically undergoes at least one crossover event (crossover assurance) but these exchanges are also strictly limited in number and widely spaced along chromosomes (crossover interference). This has implied the existence of chromosome-wide signals that regulate crossovers, but their molecular basis remains mysterious. Here we characterize a family of four related RING finger proteins in C. elegans. These proteins are recruited to the synaptonemal complex between paired homologs, where they act as two heterodimeric complexes, likely as E3 ubiquitin ligases. Genetic and cytological analysis reveals that they act with additional components to create a self-extinguishing circuit that controls crossover designation and maturation. These proteins also act at the top of a hierarchical chromosome remodeling process that enables crossovers to direct stepwise segregation. Work in diverse phyla indicates that related mechanisms mediate crossover control across eukaryotes.

cell biology↗

bioRxiv2017

Super-resolution microscopy reveals the three-dimensional organization of meiotic chromosome axes in intact C. elegans tissue

When cells enter meiosis, their chromosomes reorganize as linear arrays of chromatin loops anchored to a central axis. Meiotic chromosome axes form a platform for the assembly of the synaptonemal complex (SC), and play central roles in other meiotic processes, including homologous pairing, recombination, and chromosome segregation. However, little is known about the three-dimensional organization of components within the axes, which consist of cohesin complexes and additional meiosis-specific proteins. Here we investigate the molecular organization of meiotic chromosome axes in C. elegans through STORM and PALM superresolution imaging of intact germline tissue. By tagging one axis protein (HIM-3) with a photoconvertible fluorescent protein, we established a spatial reference for other components, which were localized using antibodies against epitope tags inserted by CRISPR/Cas9 genome editing. Using three-dimensional averaging, we determined the 3D-organization of all known components within synapsed chromosome axes to a precision of 2-5 nanometers. We find that meiosis-specific HORMA-domain proteins span a gap between cohesin complexes and the central region of the SC, consistent with their essential roles in SC assembly. Our data further suggest that the two different meiotic cohesin complexes are distinctly arranged within the axes: Cohesin complexes containing COH-3 or -4 kleisins form a central core in the central plane of the axes, whereas complexes containing REC-8 kleisin protrude above and below the plane defined by the SC. This splayed organization may help to explain the role of the chromosome axes in promoting inter-homolog repair of meiotic double strand breaks by inhibiting inter-sister repair.

cell biology↗