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The yeast motor protein, Kar3p, is essential for meiosis I.

Bascom-Slack CA, Dawson DS - J. Cell Biol. (1997)

Bottom Line: The recognition and alignment of homologous chromosomes early in meiosis is essential for their subsequent segregation at anaphase I; however, the mechanism by which this occurs is unknown.We demonstrate here that, in the absence of the molecular motor, Kar3p, meiotic cells are blocked with prophase monopolar microtubule arrays and incomplete synaptonemal complex (SC) formation. kar3 mutants exhibit very low levels of heteroallelic recombination. kar3 mutants do produce double-strand breaks that act as initiation sites for meiotic recombination in yeast, but at levels severalfold reduced from wild-type.These data are consistent with a meiotic role for Kar3p in the events that culminate in synapsis of homologues.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, Massachusetts 02111, USA.

ABSTRACT
The recognition and alignment of homologous chromosomes early in meiosis is essential for their subsequent segregation at anaphase I; however, the mechanism by which this occurs is unknown. We demonstrate here that, in the absence of the molecular motor, Kar3p, meiotic cells are blocked with prophase monopolar microtubule arrays and incomplete synaptonemal complex (SC) formation. kar3 mutants exhibit very low levels of heteroallelic recombination. kar3 mutants do produce double-strand breaks that act as initiation sites for meiotic recombination in yeast, but at levels severalfold reduced from wild-type. These data are consistent with a meiotic role for Kar3p in the events that culminate in synapsis of homologues.

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kar3 mutant cells are blocked before metaphase I. The  frequency of cells exhibiting unquestionable postprophase I morphology was determined for both the wild-type and kar3 cells.  n ⩾ 28 for each time point.
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Figure 2: kar3 mutant cells are blocked before metaphase I. The frequency of cells exhibiting unquestionable postprophase I morphology was determined for both the wild-type and kar3 cells. n ⩾ 28 for each time point.

Mentions: Staining of DNA with DAPI was also used to monitor progress through meiosis. Binucleate and tetranucleate cells were extremely rare in the mutant at late time points, indicating that these cells do not progress beyond anaphase I. To quantitatively demonstrate the lack of postprophase spindles in the mutant, we counted the number of recognizable postprophase cells compared to the total number of cells for both the wild type and mutant throughout meiosis. Only cells that exhibited unquestionable postprophase morphologies were classified as postprophase. Generally, anaphase spindles, some metaphase spindles, and binucleate and tetranucleate nuclei were easily distinguished. For wild-type cells, the fraction classified as postprophase was an underestimate as not all cells stained adequately for classification, and for others, critical features were not in the plane of focus in the photographs used for the quantification. The results shown in Fig. 2 indicate that by 12 h there is a significant difference in the number of postprophase cells for the mutant versus the wild type, and at 24 h no postprophase cells are observed in the kar3 mutants whereas 21.5% of the wild-type cells show unquestionable progression beyond prophase.


The yeast motor protein, Kar3p, is essential for meiosis I.

Bascom-Slack CA, Dawson DS - J. Cell Biol. (1997)

kar3 mutant cells are blocked before metaphase I. The  frequency of cells exhibiting unquestionable postprophase I morphology was determined for both the wild-type and kar3 cells.  n ⩾ 28 for each time point.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2139793&req=5

Figure 2: kar3 mutant cells are blocked before metaphase I. The frequency of cells exhibiting unquestionable postprophase I morphology was determined for both the wild-type and kar3 cells. n ⩾ 28 for each time point.
Mentions: Staining of DNA with DAPI was also used to monitor progress through meiosis. Binucleate and tetranucleate cells were extremely rare in the mutant at late time points, indicating that these cells do not progress beyond anaphase I. To quantitatively demonstrate the lack of postprophase spindles in the mutant, we counted the number of recognizable postprophase cells compared to the total number of cells for both the wild type and mutant throughout meiosis. Only cells that exhibited unquestionable postprophase morphologies were classified as postprophase. Generally, anaphase spindles, some metaphase spindles, and binucleate and tetranucleate nuclei were easily distinguished. For wild-type cells, the fraction classified as postprophase was an underestimate as not all cells stained adequately for classification, and for others, critical features were not in the plane of focus in the photographs used for the quantification. The results shown in Fig. 2 indicate that by 12 h there is a significant difference in the number of postprophase cells for the mutant versus the wild type, and at 24 h no postprophase cells are observed in the kar3 mutants whereas 21.5% of the wild-type cells show unquestionable progression beyond prophase.

Bottom Line: The recognition and alignment of homologous chromosomes early in meiosis is essential for their subsequent segregation at anaphase I; however, the mechanism by which this occurs is unknown.We demonstrate here that, in the absence of the molecular motor, Kar3p, meiotic cells are blocked with prophase monopolar microtubule arrays and incomplete synaptonemal complex (SC) formation. kar3 mutants exhibit very low levels of heteroallelic recombination. kar3 mutants do produce double-strand breaks that act as initiation sites for meiotic recombination in yeast, but at levels severalfold reduced from wild-type.These data are consistent with a meiotic role for Kar3p in the events that culminate in synapsis of homologues.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, Massachusetts 02111, USA.

ABSTRACT
The recognition and alignment of homologous chromosomes early in meiosis is essential for their subsequent segregation at anaphase I; however, the mechanism by which this occurs is unknown. We demonstrate here that, in the absence of the molecular motor, Kar3p, meiotic cells are blocked with prophase monopolar microtubule arrays and incomplete synaptonemal complex (SC) formation. kar3 mutants exhibit very low levels of heteroallelic recombination. kar3 mutants do produce double-strand breaks that act as initiation sites for meiotic recombination in yeast, but at levels severalfold reduced from wild-type. These data are consistent with a meiotic role for Kar3p in the events that culminate in synapsis of homologues.

Show MeSH
Related in: MedlinePlus