Excess crossovers impede faithful meiotic chromosome segregation in C. elegans

AbstractDuring meiosis, at least one crossover must form between each pair of homologous chromosomes to ensure their proper partitioning. However, most organisms limit the number of crossovers by a phenomenon called crossover interference; why this occurs is not well understood. Here we investigate the functional consequences of extra crossovers in Caenorhabditis elegans. Using a fusion chromosome that exhibits a high frequency of supernumerary crossovers, we find that essential chromosomal structures are mispatterned, subjecting chromosomes to improper spindle forces and leading to congression and segregation defects. Moreover, we uncover mechanisms that counteract these errors; anaphase I chromosome bridges were often able to resolve in a LEM-3 nuclease dependent manner, and tethers between homologs that persisted were frequently resolved during Meiosis II by a second mechanism. This study thus provides evidence that excess crossovers impact chromosome patterning and segregation, and also sheds light on how these errors are corrected.

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A compartmentalized signaling network mediates crossover control in meiosis

eLife ◽

10.7554/elife.30789 ◽

2018 ◽

Vol 7 ◽

Cited By ~ 25

Author(s):

Liangyu Zhang ◽

Simone Köhler ◽

Regina Rillo-Bohn ◽

Abby F Dernburg

Keyword(s):

Caenorhabditis Elegans ◽

Symmetry Breaking ◽

Synaptonemal Complex ◽

Chromosome Segregation ◽

Molecular Basis ◽

Liquid Crystalline ◽

Ring Finger ◽

Homologous Chromosomes ◽

Crossover Interference ◽

Ring Finger Proteins

During meiosis, each pair of homologous chromosomes typically undergoes at least one crossover (crossover assurance), but these exchanges are strictly limited in number and widely spaced along chromosomes (crossover interference). The molecular basis for this chromosome-wide regulation remains mysterious. A family of meiotic RING finger proteins has been implicated in crossover regulation across eukaryotes. Caenorhabditis elegans expresses four such proteins, of which one (ZHP-3) is known to be required for crossovers. Here we investigate the functions of ZHP-1, ZHP-2, and ZHP-4. We find that all four ZHP proteins, like their homologs in other species, localize to the synaptonemal complex, an unusual, liquid crystalline compartment that assembles between paired homologs. Together they promote accumulation of pro-crossover factors, including ZHP-3 and ZHP-4, at a single recombination intermediate, thereby patterning exchanges along paired chromosomes. These proteins also act at the top of a hierarchical, symmetry-breaking process that enables crossovers to direct accurate chromosome segregation.

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Synaptonemal complex components are required for meiotic checkpoint function in C. elegans

10.1101/052977 ◽

2016 ◽

Author(s):

Tisha Bohr ◽

Guinevere Ashley ◽

Evan Eggleston ◽

Kyra Firestone ◽

Needhi Bhalla

Keyword(s):

Synaptonemal Complex ◽

Chromosome Segregation ◽

Meiotic Chromosome ◽

Checkpoint Response ◽

Homologous Chromosomes ◽

C Elegans ◽

Homolog Pairing ◽

The Stability ◽

Complex Components

AbstractSynapsis involves the assembly of a proteinaceous structure, the synaptonemal complex (SC), between paired homologous chromosomes and is essential for proper meiotic chromosome segregation. In C. elegans, the synapsis checkpoint selectively removes nuclei with unsynapsed chromosomes by inducing apoptosis. This checkpoint depends on Pairing Centers (PCs), cis-acting sites that promote pairing and synapsis. We have hypothesized that the stability of homolog pairing at PCs is monitored by this checkpoint. Here, we report that SC components SYP-3, HTP-3, HIM-3 and HTP-1 are required for a functional synapsis checkpoint. Mutation of these components does not abolish PC function, demonstrating they are bonafide checkpoint components. Further, we identify mutant backgrounds in which the instability of homolog pairing at PCs does not correlate with the synapsis checkpoint response. Altogether, these data suggest that, in addition to homolog pairing, SC assembly may be monitored by the synapsis checkpoint.

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Condensin restructures chromosomes in preparation for meiotic divisions

The Journal of Cell Biology ◽

10.1083/jcb.200408061 ◽

2004 ◽

Vol 167 (4) ◽

pp. 613-625 ◽

Cited By ~ 73

Author(s):

Raymond C. Chan ◽

Aaron F. Severson ◽

Barbara J. Meyer

Keyword(s):

Caenorhabditis Elegans ◽

Chromosome Segregation ◽

Germ Cells ◽

Protein Complex ◽

Mitotic Chromosome ◽

Meiotic Chromosome ◽

Ordered Structure ◽

Homologous Chromosomes ◽

Sister Chromatids ◽

Chromosome Resolution

The production of haploid gametes from diploid germ cells requires two rounds of meiotic chromosome segregation after one round of replication. Accurate meiotic chromosome segregation involves the remodeling of each pair of homologous chromosomes around the site of crossover into a highly condensed and ordered structure. We showed that condensin, the protein complex needed for mitotic chromosome compaction, restructures chromosomes during meiosis in Caenorhabditis elegans. In particular, condensin promotes both meiotic chromosome condensation after crossover recombination and the remodeling of sister chromatids. Condensin helps resolve cohesin-independent linkages between sister chromatids and alleviates recombination-independent linkages between homologues. The safeguarding of chromosome resolution by condensin permits chromosome segregation and is crucial for the formation of discrete, individualized bivalent chromosomes.

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

10.1101/168948 ◽

2017 ◽

Cited By ~ 1

Author(s):

Liangyu Zhang ◽

Simone Köhler ◽

Regina Rillo-Bohn ◽

Abby F. Dernburg

Keyword(s):

Chromosome Segregation ◽

Meiotic Recombination ◽

Molecular Basis ◽

Chromosome Pair ◽

Ring Finger ◽

Cytological Analysis ◽

Homologous Chromosomes ◽

Crossover Interference ◽

C Elegans ◽

Ring Finger Proteins

AbstractMeiotic 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.

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The conserved phosphatase GSP-2/PP1 promotes germline immortality via small RNA-mediated genome silencing during meiosis

10.1101/273722 ◽

2018 ◽

Author(s):

Katherine Kretovich Billmyre ◽

Anna-lisa Doebley ◽

Bree Heestand ◽

Tony Belicard ◽

Aya Sato-Carlton ◽

...

Keyword(s):

Germ Cell ◽

Chromosome Segregation ◽

Small Rna ◽

Protein Phosphatase ◽

Germ Line ◽

Meiotic Chromosome ◽

Loss Of Function ◽

Homologous Chromosomes ◽

C Elegans ◽

Cell Immortality

AbstractGenomic silencing can promote germ cell immortality, or transgenerational maintenance of the germ line, via mechanisms that may occur during mitosis or meiosis. Here we report that the gsp-2 PP1/Glc7 phosphatase promotes germ cell immortality. We identified a separation-of-function allele of C. elegans GSP-2 that caused a meiosis-specific chromosome segregation defect and defects in transgenerational small RNA-induced genome silencing. GSP-2 is recruited to meiotic chromosomes by LAB-1, which also promoted germ cell immortality. Sterile gsp-2 and lab-1 mutant adults displayed germline degeneration, univalents and histone phosphorylation defects in oocytes, similar to small RNA genome silencing mutants. Epistasis and RNA analysis suggested that GSP-2 functions downstream of small RNAs. We conclude that a meiosis-specific function of GSP-2/LAB-1 ties small RNA-mediated silencing of the epigenome to germ cell immortality. Given that hemizygous genetic elements can drive transgenerational epigenomic silencing, and given that LAB-1 promotes pairing of homologous chromosomes and localizes to the interface between homologous chromosomes during pachytene, we suggest that discontinuities at this interface could promote nuclear silencing in a manner that depends on GSP-2.Author SummaryThe germ line of an organism is considered immortal in its capacity to give rise to an unlimited number of future generations. To protect the integrity of the germ line, mechanisms act to suppress the accumulation of transgenerational damage to the genome or epigenome. Loss of germ cell immortality can result from mutations that disrupt the small RNA-mediated silencing pathway that helps to protect the integrity of the epigenome. Here we report for the first time that the C. elegans protein phosphatase GSP-2 that promotes core chromosome biology functions during meiosis is also required for germ cell immortality. Specifically, we identified a partial loss of function allele of gsp-2 that exhibits defects in meiotic chromosome segregation and is also dysfunctional for transgenerational small RNA-mediated genome silencing. Our results are consistent with a known role of Drosophila Protein Phosphatase 1 in heterochromatin silencing, and point to a meiotic phosphatase function that is relevant to germ cell immortality, conceivably related to its roles in chromosome pairing or sister chromatid cohesion.

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Distinct Developmental Function of Two Caenorhabditis elegans Homologs of the Cohesin Subunit Scc1/Rad21

Molecular Biology of the Cell ◽

10.1091/mbc.e02-09-0603 ◽

2003 ◽

Vol 14 (6) ◽

pp. 2399-2409 ◽

Cited By ~ 21

Author(s):

Yoshiko Mito ◽

Asako Sugimoto ◽

Masayuki Yamamoto

Keyword(s):

Cell Cycle ◽

Caenorhabditis Elegans ◽

Chromosome Segregation ◽

Mitotic Chromosome ◽

Dependent Manner ◽

C Elegans ◽

Late Embryogenesis ◽

A Cell ◽

Cohesin Subunit ◽

Cycle Dependent

Cohesin, which mediates sister chromatid cohesion, is composed of four subunits, named Scc1/Rad21, Scc3, Smc1, and Smc3 in yeast. Caenorhabditis elegans has a single homolog for each of Scc3, Smc1, and Smc3, but as many as four for Scc1/Rad21 (COH-1, SCC-1/COH-2, COH-3, and REC-8). Except for REC-8 required for meiosis, function of these C. elegans proteins remains largely unknown. Herein, we examined their possible involvement in mitosis and development. Embryos depleted of the homolog of either Scc3, or Smc1, or Smc3 by RNA interference revealed a defect in mitotic chromosome segregation but not in chromosome condensation and cytokinesis. Depletion of SCC-1/COH-2 caused similar phenotypes. SCC-1/COH-2 was present in cells destined to divide. It localized to chromosomes in a cell cycle-dependent manner. Worms depleted of COH-1 arrested at either the late embryonic or the larval stage, with no indication of mitotic dysfunction. COH-1 associated chromosomes throughout the cell cycle in all somatic cells undergoing late embryogenesis or larval development. Thus, SCC-1/COH-2 and the homologs of Scc3, Smc1, and Smc3 facilitate mitotic chromosome segregation during the development, presumably by forming a cohesin complex, whereas COH-1 seems to play a role important for development but unrelated to mitosis.

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A Cuticle Collagen Encoded by the lon-3 Gene May Be a Target of TGF-β Signaling in Determining Caenorhabditis elegans Body Shape

Genetics ◽

10.1093/genetics/162.4.1631 ◽

2002 ◽

Vol 162 (4) ◽

pp. 1631-1639

Author(s):

Yo Suzuki ◽

Gail A Morris ◽

Min Han ◽

William B Wood

Keyword(s):

Caenorhabditis Elegans ◽

Body Shape ◽

Small Body ◽

Dependent Manner ◽

Loss Of Function ◽

Cellular Mechanisms ◽

C Elegans ◽

Gene Expression Analyses ◽

Dose Dependent

Abstract The signaling pathway initiated by the TGF-β family member DBL-1 in Caenorhabditis elegans controls body shape in a dose-dependent manner. Loss-of-function (lf) mutations in the dbl-1 gene cause a short, small body (Sma phenotype), whereas overexpression of dbl-1 causes a long body (Lon phenotype). To understand the cellular mechanisms underlying these phenotypes, we have isolated suppressors of the Sma phenotype resulting from a dbl-1(lf) mutation. Two of these suppressors are mutations in the lon-3 gene, of which four additional alleles are known. We show that lon-3 encodes a collagen that is a component of the C. elegans cuticle. Genetic and reporter-gene expression analyses suggest that lon-3 is involved in determination of body shape and is post-transcriptionally regulated by the dbl-1 pathway. These results support the possibility that TGF-β signaling controls C. elegans body shape by regulating cuticle composition.

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In the Model Host Caenorhabditis elegans, Sphingosine-1-Phosphate-Mediated Signaling Increases Immunity toward Human Opportunistic Bacteria

International Journal of Molecular Sciences ◽

10.3390/ijms21217813 ◽

2020 ◽

Vol 21 (21) ◽

pp. 7813

Author(s):

Kiho Lee ◽

Iliana Escobar ◽

Yeeun Jang ◽

Wooseong Kim ◽

Frederick M. Ausubel ◽

...

Keyword(s):

Caenorhabditis Elegans ◽

Stress Responses ◽

Mapk Signaling ◽

Dependent Manner ◽

Cellular Functions ◽

Kinase Gene ◽

Concentration Dependent Manner ◽

C Elegans ◽

Opportunistic Bacteria ◽

Free Living Nematode

Sphingosine-1-phophate (S1P) is a sphingolipid-derived signaling molecule that controls diverse cellular functions including cell growth, homeostasis, and stress responses. In a variety of metazoans, cytosolic S1P is transported into the extracellular space where it activates S1P receptors in a concentration-dependent manner. In the free-living nematode Caenorhabditis elegans, the spin-2 gene, which encodes a S1P transporter, is activated during Gram-positive or Gram-negative bacterial infection of the intestine. However, the role during infection of spin-2 and three additional genes in the C. elegans genome encoding other putative S1P transporters has not been elucidated. Here, we report an evolutionally conserved function for S1P and a non-canonical role for S1P transporters in the C. elegans immune response to bacterial pathogens. We found that mutations in the sphingosine kinase gene (sphk-1) or in the S1P transporter genes spin-2 or spin-3 decreased nematode survival after infection with Pseudomonas aeruginosa or Enterococcus faecalis. In contrast to spin-2 and spin-3, mutating spin-1 leads to an increase in resistance to P. aeruginosa. Consistent with these results, when wild-type C. elegans were supplemented with extracellular S1P, we found an increase in their lifespan when challenged with P. aeruginosa and E. faecalis. In comparison, spin-2 and spin-3 mutations suppressed the ability of S1P to rescue the worms from pathogen-mediated killing, whereas the spin-1 mutation had no effect on the immune-enhancing activity of S1P. S1P demonstrated no antimicrobial activity toward P. aeruginosa and Escherichia coli and only minimal activity against E. faecalis MMH594 (40 µM). These data suggest that spin-2 and spin-3, on the one hand, and spin-1, on the other hand, transport S1P across cellular membranes in opposite directions. Finally, the immune modulatory effect of S1P was diminished in C. eleganssek-1 and pmk-1 mutants, suggesting that the immunomodulatory effects of S1P are mediated by the p38 MAPK signaling pathway.

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Embryonic extracts derived from the nematode Caenorhabditis elegans remove uracil from DNA by the sequential action of uracil-DNA glycosylase and AP (apurinic/apyrimidinic) endonuclease

Biochemical Journal ◽

10.1042/bj20020375 ◽

2002 ◽

Vol 365 (2) ◽

pp. 547-553 ◽

Cited By ~ 21

Author(s):

Andrea SHATILLA ◽

Dindial RAMOTAR

Keyword(s):

Caenorhabditis Elegans ◽

Excision Repair ◽

Specific Inhibitor ◽

Dna Glycosylase ◽

Dependent Manner ◽

Nematode Caenorhabditis Elegans ◽

Uracil Dna Glycosylase ◽

Ap Endonuclease ◽

C Elegans ◽

Ap Site

DNA bases continuously undergo modifications in response to endogenous reactions such as oxidation, alkylation or deamination. The modified bases are primarily removed by DNA glycosylases, which cleave the N-glycosylic bond linking the base to the sugar, to generate an apurinic/apyrimidinic (AP) site, and this latter lesion is highly mutagenic. Previously, no study has demonstrated the processing of these lesions in the nematode Caenorhabditis elegans. Herein, we report the existence of uracil-DNA glycosylase and AP endonuclease activities in extracts derived from embryos of C. elegans. These enzyme activities were monitored using a defined 5′-end 32P-labelled 42-bp synthetic oligonucleotide substrate bearing a single uracil residue opposite guanine at position 21. The embryonic extract rapidly cleaved the substrate in a time-dependent manner to produce a 20-mer product. The extract did not excise adenine or thymine opposite guanine, although uracil opposite either adenine or thymine was processed. Addition of the highly specific inhibitor of uracil-DNA glycosylase produced by Bacillus subtilis to the extract prevented the formation of the 20-mer product, indicating that removal of uracil is catalysed by uracil-DNA glycosylase. The data suggest that the 20-mer product was generated by a sequential reaction, i.e., removal of the uracil base followed by 5′-cleavage of the AP site. Further analysis revealed that product formation was dependent upon the presence of Mg2+, suggesting that cleavage of the AP site, following uracil excision, is carried out by a Mg2+-dependent AP endonuclease. It would appear that these activities correspond to the first two steps of a putative base-excision-repair pathway in C. elegans.

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Memory of recent oxygen experience switches pheromone valence in Caenorhabditis elegans

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1618934114 ◽

2017 ◽

Vol 114 (16) ◽

pp. 4195-4200 ◽

Cited By ~ 24

Author(s):

Lorenz A. Fenk ◽

Mario de Bono

Keyword(s):

Caenorhabditis Elegans ◽

Behavioral Plasticity ◽

Prior Experience ◽

Sensory Information ◽

Dependent Manner ◽

Oxygen Environment ◽

C Elegans ◽

Sustained Change ◽

Context Dependent ◽

Physiological Correlate

Animals adjust their behavioral priorities according to momentary needs and prior experience. We show that Caenorhabditis elegans changes how it processes sensory information according to the oxygen environment it experienced recently. C. elegans acclimated to 7% O2 are aroused by CO2 and repelled by pheromones that attract animals acclimated to 21% O2. This behavioral plasticity arises from prolonged activity differences in a circuit that continuously signals O2 levels. A sustained change in the activity of O2-sensing neurons reprograms the properties of their postsynaptic partners, the RMG hub interneurons. RMG is gap-junctionally coupled to the ASK and ADL pheromone sensors that respectively drive pheromone attraction and repulsion. Prior O2 experience has opposite effects on the pheromone responsiveness of these neurons. These circuit changes provide a physiological correlate of altered pheromone valence. Our results suggest C. elegans stores a memory of recent O2 experience in the RMG circuit and illustrate how a circuit is flexibly sculpted to guide behavioral decisions in a context-dependent manner.

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