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Distinct functions of S. pombe Rec12 (Spo11) protein and Rec12-dependent crossover recombination (chiasmata) in meiosis I; and a requirement for Rec12 in meiosis II.

Sharif WD, Glick GG, Davidson MK, Wahls WP - Cell Chromosome (2002)

Bottom Line: CONCLUSIONS: Rec12 is a 345 amino acid protein required for most crossover recombination and for chiasmatic segregation of chromosomes during meiosis I.Rec12 also participates in a backup distributive (achiasmatic) system of chromosome segregation during meiosis I.In addition, catalytically-active Rec12 mediates some signal that is required for faithful equational segregation of chromosomes during meiosis II.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA. WahlsWayneP@uams.edu

ABSTRACT
BACKGROUND: In most organisms proper reductional chromosome segregation during meiosis I is strongly correlated with the presence of crossover recombination structures (chiasmata); recombination deficient mutants lack crossovers and suffer meiosis I nondisjunction. We report that these functions are separable in the fission yeast Schizosaccharomyces pombe. RESULTS: Intron mapping and expression studies confirmed that Rec12 is a member of the Spo11/Top6A topoisomerase family required for the formation of meiotic dsDNA breaks and recombination. rec12-117, rec12-D15 (), and rec12-Y98F (active site) mutants lacked most crossover recombination and chromosomes segregated abnormally to generate aneuploid meiotic products. Since S. pombe contains only three chromosome pairs, many of those aneuploid products were viable. The types of aberrant chromosome segregation were inferred from the inheritance patterns of centromere linked markers in diploid meiotic products. The rec12-117 and rec12-D15 mutants manifest segregation errors during both meiosis I and meiosis II. Remarkably, the rec12-Y98F (active site) mutant exhibited essentially normal meiosis I segregation patterns, but still exhibited meiosis II segregation errors. CONCLUSIONS: Rec12 is a 345 amino acid protein required for most crossover recombination and for chiasmatic segregation of chromosomes during meiosis I. Rec12 also participates in a backup distributive (achiasmatic) system of chromosome segregation during meiosis I. In addition, catalytically-active Rec12 mediates some signal that is required for faithful equational segregation of chromosomes during meiosis II.

No MeSH data available.


Related in: MedlinePlus

Cytological phenotypes of wild-type and rec12 mutant asci. (A-B) DIC (left) and DAPI fluorescence (right) images of asci. In addition to aberrant ascus morphology, variable spore number, and unequal DNA content, some rec12 mutant asci show evidence of trailing DNA and chromatin bridges (arrows). The data were from crosses of strains: WSP0602 × WSP0603; WSP0332 × WSP0335 or WSP0079 × WSP1799; WSP1813 × WSP1819; and WSP1556 × WSP1559. (C) Summary of cytological phenotypes in wild-type, rec12-117, rec12-D15, and rec12-Y98F. Randomly selected asci were classified based upon DNA content and distribution (black dots), spore coat formation (circles), and ascus morphology (peripheral oval) using data such as in Panel B. Between 187 and 300 asci were scored for each group. Photomicrographs corresponding to classes "f," "l," and "j" are shown in Panel B.
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Figure 3: Cytological phenotypes of wild-type and rec12 mutant asci. (A-B) DIC (left) and DAPI fluorescence (right) images of asci. In addition to aberrant ascus morphology, variable spore number, and unequal DNA content, some rec12 mutant asci show evidence of trailing DNA and chromatin bridges (arrows). The data were from crosses of strains: WSP0602 × WSP0603; WSP0332 × WSP0335 or WSP0079 × WSP1799; WSP1813 × WSP1819; and WSP1556 × WSP1559. (C) Summary of cytological phenotypes in wild-type, rec12-117, rec12-D15, and rec12-Y98F. Randomly selected asci were classified based upon DNA content and distribution (black dots), spore coat formation (circles), and ascus morphology (peripheral oval) using data such as in Panel B. Between 187 and 300 asci were scored for each group. Photomicrographs corresponding to classes "f," "l," and "j" are shown in Panel B.

Mentions: The rec12 mutant meioses are achiasmatic and would thus be expected to suffer chromosome segregation errors during meiosis I. To gain insight into this possibility, asci from meiotic cultures were stained with a DNA specific fluorescent dye (DAPI) and visualized by differential interference contrast (DIC) and fluorescence microscopy. The majority of asci from wild-type cells contained four well-rounded spores, each with a single DAPI-staining body of equal intensity (Figure 3A). The rec12 mutants were proficient at meiosis and underwent two meiotic divisions as revealed by ascus development and the distribution of chromosomes. However, each of the rec12 mutants exhibited a high frequency of chromosome segregation errors that were sometimes accompanied by defects in spore formation and/or ascus development (Figure 3B). The data from a large number of asci from each mutant are presented schematically in Figure 3C.


Distinct functions of S. pombe Rec12 (Spo11) protein and Rec12-dependent crossover recombination (chiasmata) in meiosis I; and a requirement for Rec12 in meiosis II.

Sharif WD, Glick GG, Davidson MK, Wahls WP - Cell Chromosome (2002)

Cytological phenotypes of wild-type and rec12 mutant asci. (A-B) DIC (left) and DAPI fluorescence (right) images of asci. In addition to aberrant ascus morphology, variable spore number, and unequal DNA content, some rec12 mutant asci show evidence of trailing DNA and chromatin bridges (arrows). The data were from crosses of strains: WSP0602 × WSP0603; WSP0332 × WSP0335 or WSP0079 × WSP1799; WSP1813 × WSP1819; and WSP1556 × WSP1559. (C) Summary of cytological phenotypes in wild-type, rec12-117, rec12-D15, and rec12-Y98F. Randomly selected asci were classified based upon DNA content and distribution (black dots), spore coat formation (circles), and ascus morphology (peripheral oval) using data such as in Panel B. Between 187 and 300 asci were scored for each group. Photomicrographs corresponding to classes "f," "l," and "j" are shown in Panel B.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC131009&req=5

Figure 3: Cytological phenotypes of wild-type and rec12 mutant asci. (A-B) DIC (left) and DAPI fluorescence (right) images of asci. In addition to aberrant ascus morphology, variable spore number, and unequal DNA content, some rec12 mutant asci show evidence of trailing DNA and chromatin bridges (arrows). The data were from crosses of strains: WSP0602 × WSP0603; WSP0332 × WSP0335 or WSP0079 × WSP1799; WSP1813 × WSP1819; and WSP1556 × WSP1559. (C) Summary of cytological phenotypes in wild-type, rec12-117, rec12-D15, and rec12-Y98F. Randomly selected asci were classified based upon DNA content and distribution (black dots), spore coat formation (circles), and ascus morphology (peripheral oval) using data such as in Panel B. Between 187 and 300 asci were scored for each group. Photomicrographs corresponding to classes "f," "l," and "j" are shown in Panel B.
Mentions: The rec12 mutant meioses are achiasmatic and would thus be expected to suffer chromosome segregation errors during meiosis I. To gain insight into this possibility, asci from meiotic cultures were stained with a DNA specific fluorescent dye (DAPI) and visualized by differential interference contrast (DIC) and fluorescence microscopy. The majority of asci from wild-type cells contained four well-rounded spores, each with a single DAPI-staining body of equal intensity (Figure 3A). The rec12 mutants were proficient at meiosis and underwent two meiotic divisions as revealed by ascus development and the distribution of chromosomes. However, each of the rec12 mutants exhibited a high frequency of chromosome segregation errors that were sometimes accompanied by defects in spore formation and/or ascus development (Figure 3B). The data from a large number of asci from each mutant are presented schematically in Figure 3C.

Bottom Line: CONCLUSIONS: Rec12 is a 345 amino acid protein required for most crossover recombination and for chiasmatic segregation of chromosomes during meiosis I.Rec12 also participates in a backup distributive (achiasmatic) system of chromosome segregation during meiosis I.In addition, catalytically-active Rec12 mediates some signal that is required for faithful equational segregation of chromosomes during meiosis II.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA. WahlsWayneP@uams.edu

ABSTRACT
BACKGROUND: In most organisms proper reductional chromosome segregation during meiosis I is strongly correlated with the presence of crossover recombination structures (chiasmata); recombination deficient mutants lack crossovers and suffer meiosis I nondisjunction. We report that these functions are separable in the fission yeast Schizosaccharomyces pombe. RESULTS: Intron mapping and expression studies confirmed that Rec12 is a member of the Spo11/Top6A topoisomerase family required for the formation of meiotic dsDNA breaks and recombination. rec12-117, rec12-D15 (), and rec12-Y98F (active site) mutants lacked most crossover recombination and chromosomes segregated abnormally to generate aneuploid meiotic products. Since S. pombe contains only three chromosome pairs, many of those aneuploid products were viable. The types of aberrant chromosome segregation were inferred from the inheritance patterns of centromere linked markers in diploid meiotic products. The rec12-117 and rec12-D15 mutants manifest segregation errors during both meiosis I and meiosis II. Remarkably, the rec12-Y98F (active site) mutant exhibited essentially normal meiosis I segregation patterns, but still exhibited meiosis II segregation errors. CONCLUSIONS: Rec12 is a 345 amino acid protein required for most crossover recombination and for chiasmatic segregation of chromosomes during meiosis I. Rec12 also participates in a backup distributive (achiasmatic) system of chromosome segregation during meiosis I. In addition, catalytically-active Rec12 mediates some signal that is required for faithful equational segregation of chromosomes during meiosis II.

No MeSH data available.


Related in: MedlinePlus