Limits...
Mus81 nuclease and Sgs1 helicase are essential for meiotic recombination in a protist lacking a synaptonemal complex.

Lukaszewicz A, Howard-Till RA, Loidl J - Nucleic Acids Res. (2013)

Bottom Line: We show in Tetrahymena, that homologous chromosomes fail to separate and JMs accumulate in the absence of Mus81 or Sgs1, whereas deletion of the MutLγ-component Mlh1 does not affect meiotic divisions.Thus, our results are consistent with Mus81 being part of an essential, if not the predominant, CO pathway in Tetrahymena.Tetrahymena shares the predominance of the Mus81 CO pathway with the fission yeast.

View Article: PubMed Central - PubMed

Affiliation: Department of Chromosome Biology, Max F. Perutz Laboratories, Center for Molecular Biology, University of Vienna, A-1030 Vienna, Austria.

ABSTRACT
Mus81 resolvase and Sgs1 helicase have well-established roles in mitotic DNA repair. Moreover, Mus81 is part of a minor crossover (CO) pathway in the meiosis of budding yeast, plants and vertebrates. The major pathway depends on meiosis-specific synaptonemal complex (SC) formation, ZMM proteins and the MutLγ complex for CO-directed resolution of joint molecule (JM)-recombination intermediates. Sgs1 has also been implicated in this pathway, although it may mainly promote the non-CO outcome of meiotic repair. We show in Tetrahymena, that homologous chromosomes fail to separate and JMs accumulate in the absence of Mus81 or Sgs1, whereas deletion of the MutLγ-component Mlh1 does not affect meiotic divisions. Thus, our results are consistent with Mus81 being part of an essential, if not the predominant, CO pathway in Tetrahymena. Sgs1 may exert functions similar to those in other eukaryotes. However, we propose an additional role in supporting homologous CO formation by promoting homologous over intersister interactions. Tetrahymena shares the predominance of the Mus81 CO pathway with the fission yeast. We propose that in these two organisms, which independently lost the SC during evolution, the basal set of mitotic repair proteins is sufficient for executing meiotic recombination.

Show MeSH

Related in: MedlinePlus

Expression of HJ resolvase candidate genes, Sgs1 and Mms4 localization during meiosis, and aberrant metaphase I in mus81i and sgs1i. (A) RT-PCR. Expression patterns of meiosis-specific genes SPO11 and DMC1 and the ubiquitously expressed control gene RPL21 are shown for comparison. V = vegetative cells, 0 = starving cells at the time of meiosis induction, 1–10 = h after meiosis induction. (B) Sgs1-HA (red) localizes to meiotic nuclei throughout prophase. By metaphase I it disappears. (C) Immunostained Mms4 is visible at diakinesis. (D) mus81i and sgs1i cells do not show condensed metaphase bivalents, yet association of FISH signal pairs (red) demonstrates that homologous chromosomes are paired in most nuclei. FISH signal distances were measured in 100 nuclei of the WT, mus81i and sgs1i, each. Nuclei were plotted along the X-axis according to increasing distances. Single FISH signals, indicating close pairing, were assigned a zero distance on the Y-axis. Bars in B and D: 10 µm.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3814389&req=5

gkt703-F2: Expression of HJ resolvase candidate genes, Sgs1 and Mms4 localization during meiosis, and aberrant metaphase I in mus81i and sgs1i. (A) RT-PCR. Expression patterns of meiosis-specific genes SPO11 and DMC1 and the ubiquitously expressed control gene RPL21 are shown for comparison. V = vegetative cells, 0 = starving cells at the time of meiosis induction, 1–10 = h after meiosis induction. (B) Sgs1-HA (red) localizes to meiotic nuclei throughout prophase. By metaphase I it disappears. (C) Immunostained Mms4 is visible at diakinesis. (D) mus81i and sgs1i cells do not show condensed metaphase bivalents, yet association of FISH signal pairs (red) demonstrates that homologous chromosomes are paired in most nuclei. FISH signal distances were measured in 100 nuclei of the WT, mus81i and sgs1i, each. Nuclei were plotted along the X-axis according to increasing distances. Single FISH signals, indicating close pairing, were assigned a zero distance on the Y-axis. Bars in B and D: 10 µm.

Mentions: To assess potential roles of the above-mentioned proteins in meiosis, gene expression was studied by reverse transcription-PCR (RT-PCR). As can be seen from Figure 2A, expression of SGS1 is strongest at ∼3 h after induction of meiosis, which coincides with the time when DSBs are generated and Dmc1 foci form on chromatin (30). These temporally coordinated activities are reflected by similar timing of the transcription of SPO11 and DMC1 genes. MUS81, MMS4 and MLH1 display a basal level of expression in vegetatively growing cells but are upregulated throughout meiosis. The patterns of MUS81 and MMS4 expression, with maximums at 4–5 h, are similar, which is consistent with the possibility that, like their yeast homologs, they act as a complex. Expression of the YEN1 homolog, TTHERM_00670390 peaks at 6 h, which is too late in meiosis to act as a JM resolvase. Thus, the transcription profiles of MUS81, MMS4, SGS1 and MLH1 candidates, which are in good agreement with a microarray analysis of gene expression (47), suggest their potential involvement in meiotic recombination, and we went on to characterize them further.Figure 2.


Mus81 nuclease and Sgs1 helicase are essential for meiotic recombination in a protist lacking a synaptonemal complex.

Lukaszewicz A, Howard-Till RA, Loidl J - Nucleic Acids Res. (2013)

Expression of HJ resolvase candidate genes, Sgs1 and Mms4 localization during meiosis, and aberrant metaphase I in mus81i and sgs1i. (A) RT-PCR. Expression patterns of meiosis-specific genes SPO11 and DMC1 and the ubiquitously expressed control gene RPL21 are shown for comparison. V = vegetative cells, 0 = starving cells at the time of meiosis induction, 1–10 = h after meiosis induction. (B) Sgs1-HA (red) localizes to meiotic nuclei throughout prophase. By metaphase I it disappears. (C) Immunostained Mms4 is visible at diakinesis. (D) mus81i and sgs1i cells do not show condensed metaphase bivalents, yet association of FISH signal pairs (red) demonstrates that homologous chromosomes are paired in most nuclei. FISH signal distances were measured in 100 nuclei of the WT, mus81i and sgs1i, each. Nuclei were plotted along the X-axis according to increasing distances. Single FISH signals, indicating close pairing, were assigned a zero distance on the Y-axis. Bars in B and D: 10 µm.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3814389&req=5

gkt703-F2: Expression of HJ resolvase candidate genes, Sgs1 and Mms4 localization during meiosis, and aberrant metaphase I in mus81i and sgs1i. (A) RT-PCR. Expression patterns of meiosis-specific genes SPO11 and DMC1 and the ubiquitously expressed control gene RPL21 are shown for comparison. V = vegetative cells, 0 = starving cells at the time of meiosis induction, 1–10 = h after meiosis induction. (B) Sgs1-HA (red) localizes to meiotic nuclei throughout prophase. By metaphase I it disappears. (C) Immunostained Mms4 is visible at diakinesis. (D) mus81i and sgs1i cells do not show condensed metaphase bivalents, yet association of FISH signal pairs (red) demonstrates that homologous chromosomes are paired in most nuclei. FISH signal distances were measured in 100 nuclei of the WT, mus81i and sgs1i, each. Nuclei were plotted along the X-axis according to increasing distances. Single FISH signals, indicating close pairing, were assigned a zero distance on the Y-axis. Bars in B and D: 10 µm.
Mentions: To assess potential roles of the above-mentioned proteins in meiosis, gene expression was studied by reverse transcription-PCR (RT-PCR). As can be seen from Figure 2A, expression of SGS1 is strongest at ∼3 h after induction of meiosis, which coincides with the time when DSBs are generated and Dmc1 foci form on chromatin (30). These temporally coordinated activities are reflected by similar timing of the transcription of SPO11 and DMC1 genes. MUS81, MMS4 and MLH1 display a basal level of expression in vegetatively growing cells but are upregulated throughout meiosis. The patterns of MUS81 and MMS4 expression, with maximums at 4–5 h, are similar, which is consistent with the possibility that, like their yeast homologs, they act as a complex. Expression of the YEN1 homolog, TTHERM_00670390 peaks at 6 h, which is too late in meiosis to act as a JM resolvase. Thus, the transcription profiles of MUS81, MMS4, SGS1 and MLH1 candidates, which are in good agreement with a microarray analysis of gene expression (47), suggest their potential involvement in meiotic recombination, and we went on to characterize them further.Figure 2.

Bottom Line: We show in Tetrahymena, that homologous chromosomes fail to separate and JMs accumulate in the absence of Mus81 or Sgs1, whereas deletion of the MutLγ-component Mlh1 does not affect meiotic divisions.Thus, our results are consistent with Mus81 being part of an essential, if not the predominant, CO pathway in Tetrahymena.Tetrahymena shares the predominance of the Mus81 CO pathway with the fission yeast.

View Article: PubMed Central - PubMed

Affiliation: Department of Chromosome Biology, Max F. Perutz Laboratories, Center for Molecular Biology, University of Vienna, A-1030 Vienna, Austria.

ABSTRACT
Mus81 resolvase and Sgs1 helicase have well-established roles in mitotic DNA repair. Moreover, Mus81 is part of a minor crossover (CO) pathway in the meiosis of budding yeast, plants and vertebrates. The major pathway depends on meiosis-specific synaptonemal complex (SC) formation, ZMM proteins and the MutLγ complex for CO-directed resolution of joint molecule (JM)-recombination intermediates. Sgs1 has also been implicated in this pathway, although it may mainly promote the non-CO outcome of meiotic repair. We show in Tetrahymena, that homologous chromosomes fail to separate and JMs accumulate in the absence of Mus81 or Sgs1, whereas deletion of the MutLγ-component Mlh1 does not affect meiotic divisions. Thus, our results are consistent with Mus81 being part of an essential, if not the predominant, CO pathway in Tetrahymena. Sgs1 may exert functions similar to those in other eukaryotes. However, we propose an additional role in supporting homologous CO formation by promoting homologous over intersister interactions. Tetrahymena shares the predominance of the Mus81 CO pathway with the fission yeast. We propose that in these two organisms, which independently lost the SC during evolution, the basal set of mitotic repair proteins is sufficient for executing meiotic recombination.

Show MeSH
Related in: MedlinePlus