Recombination Can Partially Substitute for SPO13 in Regulating Meiosis I in Budding Yeast

Abstract Recombination and chromosome synapsis bring homologous chromosomes together, creating chiasmata that ensure accurate disjunction during reductional division. SPO13 is a key gene required for meiosis I (MI) reductional segregation, but dispensable for recombination, in Saccharomyces cerevisiae. Absence of SPO13 leads to single-division meiosis where reductional segregation is largely eliminated, but other meiotic events occur relatively normally. This phenotype allows haploids to produce viable meiotic products. Spo13p is thought to act by delaying nuclear division until sister centromeres/chromatids undergo proper cohesion for segregation to the same pole at MI. In the present study, a search for new spo13-like mutations that allow haploid meiosis recovered only new spo13 alleles. Unexpectedly, an unusual reduced-expression allele (spo13-23) was recovered that behaves similarly to a null mutant in haploids but to a wild-type allele in diploids, dependent on the presence of recombining homologs rather than on a diploid genome. This finding demonstrates that in addition to promoting accurate homolog disjunction, recombination can also function to partially substitute for SPO13 in promoting sister cohesion. Analysis of various recombination-defective mutants indicates that this contribution of recombination to reductional segregation requires full levels of crossing over. The implications of these results regarding SPO13 function are discussed.

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The Arabidopsis HOP2 Gene Has a Role in Preventing illegitimate Exchanges between Nonhomologous Chromosomes

10.1101/2021.08.04.455073 ◽

2021 ◽

Author(s):

YIsell Farahani-Tafreshi ◽

Chun Wei ◽

Peilu Gan ◽

Jenya Daradur ◽

C. Daniel Riggs ◽

...

Keyword(s):

Active Role ◽

Crossing Over ◽

Wild Type ◽

Positive Role ◽

Homologous Chromosomes ◽

Chromosome Synapsis ◽

Radiation Induced ◽

Nonhomologous Chromosome ◽

Chromosome Exchanges

Meiotic homologous chromosomes pair up and undergo crossing over. In many eukaryotes both intimate pairing and crossing over require the induction of double stranded breaks (DSBs) and subsequent repair via Homologous Recombination (HR). In these organisms, two key proteins are the recombinases RAD51 and DMC1. Recombinase-modulators HOP2 and MND1 have been identified as proteins that assist RAD51 and DMC1 and are needed to promote stabilized pairing. We have probed the nature of the genetic lesions seen in hop2 mutants and looked at the role of HOP2 in the fidelity of genetic exchanges. Using γH2AX as a marker for unrepaired DSBs we found that hop2-1 and mnd1 mutants have different appearance/disappearance for DSBs than wild type, but all DSBs are repaired by mid-late pachytene. Therefore, the bridges and fragments seen from metaphase I onward are due to mis-repaired DSBs, not unrepaired ones. Studying Arabidopsis haploid meiocytes we found that wild type haploids produced the expected five univalents, but hop2-1 haploids suffered many illegitimate exchanges that were stable enough to produce bridged chromosomes during segregation. Our results suggest that HOP2 has a significant active role in preventing nonhomologous associations. We also found evidence that HOP2 plays a role in preventing illegitimate exchanges during repair of radiation-induced DSBs in rapidly dividing petal cells. Thus, HOP2 plays both a positive role in promoting homologous chromosome synapsis and a separable role in preventing nonhomologous chromosome exchanges. Possible mechanisms for this second important role are discussed.

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Saccharomyces cerevisiae Mer3 Is a DNA Helicase Involved in Meiotic Crossing Over

Molecular and Cellular Biology ◽

10.1128/mcb.22.10.3281-3291.2002 ◽

2002 ◽

Vol 22 (10) ◽

pp. 3281-3291 ◽

Cited By ~ 39

Author(s):

Takuro Nakagawa ◽

Richard D. Kolodner

Keyword(s):

Saccharomyces Cerevisiae ◽

Dna Helicase ◽

Double Strand Breaks ◽

Crossing Over ◽

Helicase Activity ◽

Wild Type ◽

Rna Helicases ◽

Conserved Residues ◽

Strand Breaks ◽

Homologous Chromosomes

ABSTRACT Crossing over is regulated to occur at least once per each pair of homologous chromosomes during meiotic prophase to ensure proper segregation of chromosomes at the first meiotic division. In a mer3 deletion mutant of Saccharomyces cerevisiae, crossing over is decreased, and the distribution of the crossovers that occur is random. The predicted Mer3 protein contains seven motifs characteristic of the DExH box type of DNA/RNA helicases. The mer3G166D and the mer3K167A mutation, amino acid substitutions of conserved residues in a putative nucleotide-binding domain of the helicase motifs caused a defect in the transition of meiosis-specific double-strand breaks to later intermediates, decreased crossing over, and reduced crossover interference. The purified Mer3 protein was found to have DNA helicase activity. This helicase activity was reduced by the mer3GD mutation to <1% of the wild-type activity, even though binding of the mutant protein to single- and double-strand DNA was unaffected. The mer3KA mutation eliminated the ATPase activity of the wild-type protein. These results demonstrate that Mer3 is a DNA helicase that functions in meiotic crossing over.

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Effects of Homology, Size and Exchange on the Meiotic Segregation of Model Chromosomes in Saccharomyces cerevisiae

Genetics ◽

10.1093/genetics/142.1.79 ◽

1996 ◽

Vol 142 (1) ◽

pp. 79-89 ◽

Cited By ~ 2

Author(s):

Lyle O Ross ◽

Susannah Rankin ◽

Michèle F Shuster ◽

Dean S Dawson

Keyword(s):

Saccharomyces Cerevisiae ◽

Dna Sequences ◽

Crossing Over ◽

Chromosome Size ◽

Meiotic Segregation ◽

Yeast Saccharomyces Cerevisiae ◽

Homologous Chromosomes ◽

Reciprocal Recombination ◽

Eukaryotic Organisms ◽

Meiosis I

In most eukaryotic organisms, chiasmata, the connections formed between homologous chromosomes as a consequence of crossing over, are important for ensuring that the homologues move away from each other at meiosis I. Some organisms have the capacity to partition the rare homologues that have failed to experience reciprocal recombination. The yeast Saccharomyces cerevisiae is able to correctly partition achiasmate homologues with low fidelity by a mechanism that is largely unknown. It is possible to test which parameters affect the ability of achiasmate chromosomes to segregate by constructing strains that will have three achiasmate chromosomes at the time of meiosis. The meiotic partitioning of these chromosomes can be monitored to determine which ones segregate away from each other at meiosis I. This approach was used to test the influence of homologous yeast DNA sequences, recombination intiation sites, chromosome size and crossing over on the meiotic segregation of the model chromosomes. Chrome some size had no effect on achiasmate segregation. The influence of homologous yeast sequences on the segregation of noncrossover model chromosomes was negligible. In meioses in which two of the three model chromosomes experienced a crossover, they nearly always disjoined at meiosis I.

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The rec102 mutant of yeast is defective in meiotic recombination and chromosome synapsis.

Genetics ◽

10.1093/genetics/130.1.59 ◽

1992 ◽

Vol 130 (1) ◽

pp. 59-69

Author(s):

J Bhargava ◽

J Engebrecht ◽

G S Roeder

Keyword(s):

Synaptonemal Complex ◽

Chromosome Segregation ◽

Meiotic Recombination ◽

Meiotic Chromosome ◽

Crossing Over ◽

Homologous Chromosomes ◽

Chromosome Synapsis ◽

Recombination Pathway ◽

Yeast Mutants ◽

Meiosis I

Abstract A mutation at the REC102 locus was identified in a screen for yeast mutants that produce inviable spores. rec102 spore lethality is rescued by a spo13 mutation, which causes cells to bypass the meiosis I division. The rec102 mutation completely eliminates meiotically induced gene conversion and crossing over but has no effect on mitotic recombination frequencies. Cytological studies indicate that the rec102 mutant makes axial elements (precursors to the synaptonemal complex), but homologous chromosomes fail to synapse. In addition, meiotic chromosome segregation is significantly delayed in rec102 strains. Studies of double and triple mutants indicate that the REC102 protein acts before the RAD52 gene product in the meiotic recombination pathway. The REC102 gene was cloned based on complementation of the mutant defect and the gene was mapped to chromosome XII between CDC25 and STE11.

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A computational approach to estimating nondisjunction frequency in Saccharomyces cerevisiae

10.1101/024570 ◽

2015 ◽

Author(s):

Daniel Chu ◽

Sean M Burgess

Keyword(s):

Saccharomyces Cerevisiae ◽

Model Organism ◽

Computational Approach ◽

Published Data ◽

Wild Type ◽

Homologous Chromosomes ◽

Epistasis Analysis ◽

Special Strain ◽

Type Strains ◽

Meiosis I

Errors segregating homologous chromosomes during meiosis result in the formation of aneuploid gametes and are the largest contributing factor to birth defects and spontaneous abortions in humans. Saccharomyces cerevisiae has long served as a model organism for studying the gene network supporting normal chromosome segregation. Current methods of measuring homolog nondisjunction frequencies are laborious and involve dissecting thousands of tetrads to detect missegregation of individually marked chromosomes. Here we describe a holistic computational approach to determine the relative contributions of meiosis I nondisjunction and random spore death in mutants with reduced spore viability. These values are based on best-fit distributions of 4, 3, 2, 1, and 0 viable-spore tetrads to observed distributions in mutant and wild-type strains. We show proof-of-principle using published data sets that the calculated average meiosis I nondisjunction frequency closely matches empirically determined values. This analysis also points to meiosis I nondisjunction as an intrinsic component of spore inviability in wild-type strains. We uncover two classes of mutants that show distinct relationships between nondisjunction death and random spore death. Class I mutants, including those with known defects in establishing and maintaining the physical engagement of homologous chromosomes display a 4-fold greater ratio of nondisjunction death to random spore death compared to Class II mutants, which include those with defects in sister chromatid cohesion. Low numbers of required tetrads facilitates epistasis analysis to probe genetic interactions. Finally the application of the R-Scripts does not require any special strain construction and can be applied to previously observed tetrad distributions.

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The Budding Yeast Msh4 Protein Functions in Chromosome Synapsis and the Regulation of Crossover Distribution

Genetics ◽

10.1093/genetics/158.3.1013 ◽

2001 ◽

Vol 158 (3) ◽

pp. 1013-1025 ◽

Cited By ~ 7

Author(s):

Janet E Novak ◽

Petra B Ross-Macdonald ◽

G Shirleen Roeder

Keyword(s):

Mismatch Repair ◽

Budding Yeast ◽

Null Mutation ◽

Crossing Over ◽

Wild Type ◽

Crossover Interference ◽

Meiotic Chromosomes ◽

Chromosome Synapsis ◽

Protein Functions ◽

Or Gene

AbstractThe budding yeast MSH4 gene encodes a MutS homolog produced specifically in meiotic cells. Msh4 is not required for meiotic mismatch repair or gene conversion, but it is required for wild-type levels of crossing over. Here, we show that a msh4 null mutation substantially decreases crossover interference. With respect to the defect in interference and the level of crossing over, msh4 is similar to the zip1 mutant, which lacks a structural component of the synaptonemal complex (SC). Furthermore, epistasis tests indicate that msh4 and zip1 affect the same subset of meiotic crossovers. In the msh4 mutant, SC formation is delayed compared to wild type, and full synapsis is achieved in only about half of all nuclei. The simultaneous defects in synapsis and interference observed in msh4 (and also zip1 and ndj1/tam1) suggest a role for the SC in mediating interference. The Msh4 protein localizes to discrete foci on meiotic chromosomes and colocalizes with Zip2, a protein involved in the initiation of chromosome synapsis. Both Zip2 and Zip1 are required for the normal localization of Msh4 to chromosomes, raising the possibility that the zip1 and zip2 defects in crossing over are indirect, resulting from the failure to localize Msh4 properly.

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Nonrecombinant meiosis I nondisjunction in Saccharomyces cerevisiae induced by tRNA ochre suppressors.

Genetics ◽

10.1093/genetics/123.1.81 ◽

1989 ◽

Vol 123 (1) ◽

pp. 81-95 ◽

Cited By ~ 1

Author(s):

E J Louis ◽

J E Haber

Keyword(s):

Saccharomyces Cerevisiae ◽

Mitotic Chromosome ◽

Stop Codon ◽

Fold Increase ◽

Wild Type ◽

Yeast Saccharomyces Cerevisiae ◽

Nonsense Mutations ◽

Chromosome Iii ◽

Meiosis I ◽

Chromosome Nondisjunction

Abstract The presence of the tRNA ochre suppressors SUP11 and SUP5 is found to induce meiosis I nondisjunction in the yeast Saccharomyces cerevisiae. The induction increases with increasing dosage of the suppressor and decreases in the presence of an antisuppressor. The effect is independent of the chromosomal location of SUP11. Each of five different chromosomes monitored exhibited nondisjunction at frequencies of 0.1%-1.1% of random spores, which is a 16-160-fold increase over wild-type levels. Increased nondisjunction is reflected by a marked increase in tetrads with two and zero viable spores. In the case of chromosome III, for which a 50-cM map interval was monitored, the resulting disomes are all in the parental nonrecombinant configuration. Recombination along chromosome III appears normal both in meioses that have no nondisjunction and in meioses for which there was nondisjunction of another chromosome. We propose that a proportion of one or more proteins involved in chromosome pairing, recombination or segregation are aberrant due to translational read-through of the normal ochre stop codon. Hygromycin B, an antibiotic that can suppress nonsense mutations via translational read-through, also induces nonrecombinant meiosis I nondisjunction. Increases in mistranslation, therefore, increase the production of aneuploids during meiosis. There was no observable effect of SUP11 on mitotic chromosome nondisjunction; however some disomes caused SUP11 ade2-ochre strains to appear white or red, instead of pink.

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Shugoshin Promotes Sister Kinetochore Biorientation in Saccharomyces cerevisiae

Molecular Biology of the Cell ◽

10.1091/mbc.e07-06-0584 ◽

2008 ◽

Vol 19 (3) ◽

pp. 1199-1209 ◽

Cited By ~ 36

Author(s):

Brendan M. Kiburz ◽

Angelika Amon ◽

Adele L. Marston

Keyword(s):

Saccharomyces Cerevisiae ◽

Chromosome Segregation ◽

Minor Role ◽

Meiotic Cell ◽

Homologous Chromosomes ◽

Cell Divisions ◽

Sister Chromatids ◽

Sister Kinetochore ◽

A Minor ◽

Meiosis I

Chromosome segregation must be executed accurately during both mitotic and meiotic cell divisions. Sgo1 plays a key role in ensuring faithful chromosome segregation in at least two ways. During meiosis this protein regulates the removal of cohesins, the proteins that hold sister chromatids together, from chromosomes. During mitosis, Sgo1 is required for sensing the absence of tension caused by sister kinetochores not being attached to microtubules emanating from opposite poles. Here we describe a differential requirement for Sgo1 in the segregation of homologous chromosomes and sister chromatids. Sgo1 plays only a minor role in segregating homologous chromosomes at meiosis I. In contrast, Sgo1 is important to bias sister kinetochores toward biorientation. We suggest that Sgo1 acts at sister kinetochores to promote their biorientation.

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ZYP1 is required for obligate cross-over formation and cross-over interference in Arabidopsis

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2021671118 ◽

2021 ◽

Vol 118 (14) ◽

pp. e2021671118

Author(s):

Martin G. France ◽

Janina Enderle ◽

Sarah Röhrig ◽

Holger Puchta ◽

F. Chris H. Franklin ◽

...

Keyword(s):

Genetic Analysis ◽

Synaptonemal Complex ◽

Class Ii ◽

Class I ◽

Crossing Over ◽

Wild Type ◽

Homologous Chromosomes ◽

Virtual Absence ◽

Meiotic Progression ◽

Null Mutants

The synaptonemal complex is a tripartite proteinaceous ultrastructure that forms between homologous chromosomes during prophase I of meiosis in the majority of eukaryotes. It is characterized by the coordinated installation of transverse filament proteins between two lateral elements and is required for wild-type levels of crossing over and meiotic progression. We have generated null mutants of the duplicated Arabidopsis transverse filament genes zyp1a and zyp1b using a combination of T-DNA insertional mutants and targeted CRISPR/Cas mutagenesis. Cytological and genetic analysis of the zyp1 null mutants reveals loss of the obligate chiasma, an increase in recombination map length by 1.3- to 1.7-fold and a virtual absence of cross-over (CO) interference, determined by a significant increase in the number of double COs. At diplotene, the numbers of HEI10 foci, a marker for Class I interference-sensitive COs, are twofold greater in the zyp1 mutant compared to wild type. The increase in recombination in zyp1 does not appear to be due to the Class II interference-insensitive COs as chiasmata were reduced by ∼52% in msh5/zyp1 compared to msh5. These data suggest that ZYP1 limits the formation of closely spaced Class I COs in Arabidopsis. Our data indicate that installation of ZYP1 occurs at ASY1-labeled axial bridges and that loss of the protein disrupts progressive coalignment of the chromosome axes.

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Disruption of regulatory gene GAL80 in Saccharomyces cerevisiae: effects on carbon-controlled regulation of the galactose/melibiose pathway genes

Molecular and Cellular Biology ◽

10.1128/mcb.4.8.1521-1527.1984 ◽

1984 ◽

Vol 4 (8) ◽

pp. 1521-1527

Author(s):

T E Torchia ◽

R W Hamilton ◽

C L Cano ◽

J E Hopper

Keyword(s):

Saccharomyces Cerevisiae ◽

Catabolite Repression ◽

Carbon Catabolite Repression ◽

Regulatory Gene ◽

Negative Regulator ◽

Null Mutation ◽

Null Mutant ◽

Wild Type

In Saccharomyces cerevisiae, the transcriptional expression of the galactose-melibiose catabolic pathway genes is under the control of at least three regulatory genes, GAL4, GAL80, and GAL3. We have isolated the GAL80 gene and have studied the effect of a null mutation on the carbon-controlled regulation of the MEL1 and GAL cluster genes. The null mutation was achieved in vivo by replacing the chromosomal wild-type GAL80 allele with an in vitro-created GAL80 deletion-disruption mutation. Enzyme activities and RNA levels for the GAL cluster and MEL1 genes were constitutively expressed in the null mutant strain grown on glycerol-lactate and were higher than in the isogenic wild-type yeast strain when compared after growth on galactose. Carbon catabolite repression of the GAL cluster and MEL1 genes, which occurs at the level of transcription, is retained in the null mutant. Deletion of the GAL80 gene in a gal4 cell does not restore GAL cluster and MEL1 gene expression. The data demonstrate that (i) the GAL80 protein is a purely negative regulator, (ii) the GAL80 protein does not mediate carbon catabolite repression, and (iii) the GAL4 protein is not simply an antagonizer of GAL80-mediated repression.

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