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Cell, Vol. 123, 397–407, November 4, 2005, Copyright ©2005 by Elsevier Inc. DOI 10.1016/j.cell.2005.09.
Hong-Guo Yu and Douglas Koshland* Howard Hughes Medical Institute/Carnegie Institution Department of Embryology Baltimore, Maryland 21218 (SMC) family proteins and several additional non-SMC subunits. By studying the function and regulation of cohesin and condensin in meiosis, it has been possible to begin to address the mechanism for the coordination of sister chromatid cohesion, condensation, and recombination. Cohesin is loaded on the newly replicated sister chromatids during meiotic S phase to generate cohesion around the centromeres and along the arms (reviewed by Nasmyth and Haering ). As a consequence of sister chromatid cohesion on the arms and reciprocal recombination between homologs, the homologs become physically linked (see diagram in Figure 1A). This linkage is critical to a tension-sensing mechanism that ensures that homologs attach to microtubules from opposite poles of the meiosis I spindle. To initiate anaphase I and allow homologs to separate, homolog linkage is dissolved by removing cohesin from the arms (Figure 1A, steps d and e). To achieve this, separase, a cysteine protease, is activated by the degradation of its inhibitor, securin (Buonomo et al., 2000; Kitajima et al., 2003). Separase then cleaves a cohesin subunit, Rec8, resulting in cohesin dissociation from the chromosome arms. Rec8 phosphorylation by the Aurora-B kinase AIR-2 in C. elegans and by the Pololike kinase Cdc5 in yeast is also required for cohesin removal, possibly because phosphorylated Rec8 is a better separase substrate (Rogers et al., 2002; Clyne et al., 2003; Lee and Amon, 2003). Separase fails to cleave a subset of cohesin proximal to the centromeres because it is protected by MEI-S332/Sgo1 (Kerrebrock et al., 1995; Katis et al., 2004; Kitajima et al., 2004; Marston et al., 2004). In meiosis II (MII), this centromere proximal cohesion is used, as in mitosis, to ensure sister chromatids segregate from each other. Like cohesin, condensin also plays a critical role in meiosis. In prophase of meiosis, condensin is activated to help promote chromosome compaction and individualization in both yeast and C. elegans (Yu and Koshland, 2003; Chan et al., 2004). Condensin together with cohesin is also required for formation of the synaptonemal complex, a protein filament that forms between homologs and regulates homologous recombination to ensure proper chromosome segregation (Yu and Koshland, 2003). Another meiotic function for condensin is suggested from an unusual phenotype of condensin mutants in budding yeast and C. elegans. Portions of the chromosomes lag between the spindle poles of the elongating spindle, forming chromosome bridges. In condensin mutants of budding yeast, the formation of these bridges is dependent upon recombination (Yu and Koshland, 2003). In addition, the bridged region contains tightly paired telomeres from homologs of chromosome V. Based on these two observations, we postulated an explanation for chromosome bridging. During meiosis, homologs are linked by recombination. In condensin mutants, these linkages are not dissolved efficiently. As a result, homologs remain inappropriately paired and cannot be properly segregated when the spindle elongates, leading to the bridging phenotype.
Condensin appears to promote cohesin removal through the activation of Cdc5. Percent paired GFP spots for wt was less than 0. Red dots represent cohesin. We discuss the importance of these results for understanding chromosome morphogenesis and for coordinating chromosome morphogenesis in meiosis. and to determine condensin’s role in dissolving the linkage. The similarity in phenotype between mutations in different condensin subunits sug- . Error bars show the standard error. Results Condensin Is Required for Dissolving Homolog Linkage at Anaphase I Our previous studies had shown that condensin mutants caused chromosome bridges in MI.Cell 398 Figure 1. 200–500 wt and mutant cells were scored for paired GFP spots at 8. DNA was stained by DAPI. d—removal of armassociated cohesin allows the separation of homologs (e). Wild-type and ycs4-2 cells were induced to enter meiosis and then raised to the nonpermissive temperature for ycs4-2 inactivation. 10. centromeres and telomeres of chromosome V homologs are separated greater than 99% of time as evidenced by the detection of separated GFP spots (Figures 1C and 1D).5%. (A) A diagram showing homolog separation during MI. Indeed. ycs4-2 cells fail to separate efficiently telomeres of chromosome V homologs. Thus. when homologs have normally segregated from each other. and in one condensin mutant. the Polo-like kinase of budding yeast. that is between telophase I (elongated spindles and absence of Pds1 staining. Condensin helps dissolve these linkages by promoting the removal of a subset of cohesin prior to and possibly also at the onset of anaphase I. a—meiotic S phase. In order to better understand this potential new function for condensin. condensin appears to be required to dissolve recombination-dependent linkages between homologs. in post-anaphase I wild-type cells. and ycs4-2 rec8 . the molecular function of condensin in this resolution is unknown. To better understand this failure to dissolve pairing between telomeres. however. see Figure S1 in the Supplemental Data available with this article online) and early MII (two short spindles). c—homologs are biooriented on the meiosis I spindle. Sister Chromatid Cohesion Blocks Homolog Separation in Condensin Mutant ycs4-2 All strains were induced to enter meiosis at 23°C for 1 hr and shifted to 34°C (the nonpermissive temperature for ycs4-2). and 12 hr after induction of meiosis. Data shown are averages. ycg1-2. we initiated experiments to characterize the spatial and temporal characteristics of the homolog linkages. The number of GFP spots were scored in cells post-anaphase I. Our results suggest that the homolog linkages in anaphase I of condensin mutants reflect the persistence of the normal linkages that form in prophase I as consequence of reciprocal exchange and sister chromatid cohesion. (D) Quantitation of paired GFP spots in postanaphase I (telophase I to metaphase II) cells. these bridges contained paired telomeres from homologs of chromosome V (Yu and Koshland. as evidenced by a single GFP spot in approximately 13% of post-anaphase I cells (Figures 1C and 1D). Green arrows indicate the pulling direction of the kinetochore microtubule. Failure to remove arm-associated cohesin leads to aberrant separation of homologs (steps f and g). Centromeres are shown as black ovals. b—crossover between homologs. A temperature-sensitive allele (ycs4-2) of the Ycs4 subunit of condensin was introduced into a strain in which the two homologs of chromosome V were marked with the TetO/TetR-GFP system either at the centromere or at the right telomere (Figure 1B). To determine homolog separation at anaphase I. ycs4-2. we first asked whether a similar defect could be observed in other condensin mutants. (B) A schematic representation of GFPmarked loci on chromosomes IV and V. 2003). However. Centromeres of chromosome V homologs segregate with similar efficiency in ycs4-2 cells. (C) Representative images showing segregation of GFP-marked telomeres from homologs of chromosome V in wt. Nuclei spreads were prepared and subjected to indirect immunofluorescence (C and D). rec8 . to assess the molecular basis of the linkage. A pair of homologs are shown as gray and black bars.
in wild-type cells. Therefore. This result suggests that in condensin mutants. 2000). While we cannot rule this possibility out. while homologous telomeres from chromosome IV often remained paired (29% in post-anaphase I cells. In ycs4-2 rec8 . This pulling should separate unlinked arm sequences apart as well. we attempted to remove the persistent cohesin in condensin mutants by enhancing the cell’s ability to inactivate cohesin in anaphase I. we asked whether in ycs4-2 cells chromosome-associated cohesin remains inappropriately on the arms of homologs after anaphase I. the deletion of Rec8 may eliminate linkages by reducing recombination rather than eliminating cohesion. To disrupt sister chromatid cohesion during meiosis. In this case. Unlike rec8 . chromosome bridging between homologs results from cohesin-dependent linkage between most homologs and cohesin-independent linkage between the rDNA repeats. then the inactivation of cohesin should allow homologs to segregate. The nature of this linkage at the rDNA and condensin’s role in dissolving it both in mitosis and meiosis is the subject of additional studies. These results strongly suggest that condensin is required for the efficient removal of cohesin from chromosome arms. suggesting that some homologs remain linked even in the absence of cohesin (Figure S4).. Figure 1D). This result is consistent with the hypothesis that homolog linkage occurs in condensin mutants because of a failure to remove cohesin. wild-type cells have Rec8 and Smc1 foci near the spindle pole bodies consistent with their localization to centromeres but not arm regions of chromosomes. If the persistence of cohesin and in turn sister chromatid cohesion on chromosome arms is the cause of homolog linkages in condensin mutants. To circumvent this caveat. with GFP tethered at one of three loci: centromereproximal (12 kb to CEN4). Thus. 2004. Since we showed previously that recombination is necessary for homolog linkage in condensin mutants (Yu and Koshland. Nuclear spreads were prepared from these strains and then processed for indirect immunofluorescence (Figures 2A and S2). REC8 or SMC1. a mutant allele of another condensin subunit (Figure 2A). Sullivan et al. While chromosome V homologs separate efficiently in ycs4-2 rec8 or ycs4-2 PDMC1ESP1 cells.. Alternatively. After anaphase I. the middle of the chromosome arm (482 kb to CEN4). The arm locus also remained paired. Figure 1D). and telomere pairing causes unlinked arm regions to overlap occasionally. in condensin mutants. the centromere. less than 2% of anaphase I cells exhibited linkage at telomere V as compared to 13% in ycs4-2 cells (Figure 1D). 1999.Condensin Mediates Cohesin Removal 399 gests that a function of the condensin complex is needed for the efficient resolution of linkages between telomeres of chromosome V homologs. To assess whether there is a defect in cohesin removal in condensin mutants. the second largest. ycs4-2 cells with bridges have Rec8 and Smc1 localized throughout the chromosomes (Figures 2A and S2). specifically the removal of cohesin and the dissolution of sister chromatid cohesion on chromosome arms (Figure 1A). These strains were induced to undergo meiosis. it is indeed the persistence of cohesin on chromosome arms that prevents the dissolution of homolog linkage. Condensin Is Required to Remove Cohesin from Chromosome Arms in MI The persistence of homolog linkages post-anaphase I might reflect that these linkages result from an aberrant process and cannot be dissolved by normal meiotic machinery. Chromosome armassociated Rec8 is not removed efficiently in ycg1-2. and then analyzed for homolog pairing postanaphase I. In contrast. we generated additional wildtype and ycs4-2 strains in which we marked both homologs of chromosome IV (1532 kb). condensin is also required to dissolve cohesin-independent linkages between sister chromatids that occur at the rDNA (D’Amours et al. Interestingly.. .. This reduced frequency could reflect that homolog linkage is restricted to telomeres. we introduced a null allele of REC8 (rec8 ) into ycs4-2. To follow chromosome bound cohesin. and telomere regions of chromosome IV homologs all segregated from each other greater than 95% of the time (data not shown). the expression of ESP1 was increased about 2-fold in meiosis by replacing one copy of the endogenous ESP1 promoter with the DMC1 promoter (data not shown). the efficient segregation of the centromere sequences indicates that the homologs are being pulled apart. This cohesinindependent bridging is due to a failure to separate the ribosomal DNA (rDNA) repeats on homologs of chromosome XII (Figure S4). 2004). and the telomere-proximal (w5 kb from the end of the chromosome. the linkages would persist post-anaphase I in condensin mutants because of a defect in a normal pathway to dissolve these linkages. Therefore. our data suggest that condensin is needed to dissolve homolog linkages both on arms and telomeres. after anaphase I. albeit by a reduced frequency (14%. CEN4 segregated to opposite poles in ycs4-2 as efficiently as wild-type. To assess whether condensin is required for dissolving linkages between other homologs and at places other than the telomere. Cha et al. Our interpretation of our results with cohesin condensin double mutants is complicated by the fact that cohesin is needed for normal levels of meiotic recombination and cell cycle progression (Klein et al. we favor the interpretation that the presence of paired arm sequences in ycs4-2 mutants reflects the existence of homolog linkages on the arms. arm. In wild-type cells. Figure 1B). this increased separase expression in condensin mutants caused a 2-fold reduction of Rec8 on chromosome arms and a greater than 2-fold reduction in the pairing of chromosome V homologs in post-anaphase I cells (Figures 2B and 2C). in mitosis. condensin is required to help dissolve sister chromatid cohesion on chromosome arms. this increased separase expression had no detectable effect on the level of recombination (Figure S3). these linkages may be produced by the normal pathway of reciprocal recombination and sister chromatid cohesion in prophase I. chromosome bridging is still observed in these double mutants. 2003). raised to the nonpermissive temperature to inactivate condensin. For this purpose. That is. we generated YCS4 and ycs4-2 strains with epitope tags on two cohesin subunits. However.
1998. Spindle morphology indicates that these cells have entered into MII. the removal of a subset of cohesin during prophase I or metaphase I had not been addressed. SCC3. We used spindle and chromosome morphology to identify nuclei at the stages prior to anaphase I. 2000). and the remainder is removed at the onset of anaphase by a second pathway (Losada et al. 2003). chromosomes are no longer individualized. the presumptive pericentric regions (top panels). an activator of the anaphase promoting complex (Lee and Amon. These observations suggest that a subset of meiotic cohesin is removed from the chromosomes between prophase I and metaphase I. chromosome bound Scc3 and Smc1 are also reduced at metaphase I compared to prophase I (Figures 3E and S5). While previous studies have shown that meiotic cohesin is removed at the onset of anaphase I (Buonomo et al. Waizenegger et al. we analyzed chromosome-associated cohesin in cells that were unable to progress beyond metaphase I because they lacked Cdc20 (PCLB2CDC20). Condensin Promotes Cohesin Removal during Meiosis I Nuclei spreads were performed on cells induced to enter meiosis at 23°C for 1 hr and shifted to 34°C for 9 hr.Cell 400 Figure 2. we found that the amount of chromosome-associated cohesin in cells arrested in metaphase I is reduced to about 50% of prophase I for both Rec8 and Scc3 (Figures 3C. A subset of cohesin dissociates from chromosomes at prophase by one pathway. and the amount of chromosomal bound cohesin subunit was quantified by indirect immunofluorescence (Figures 3 and S5). 3D. we turned to studies of metazoan mitosis. Prophase I (in particular pachytene) cells have morphologically distinct and individualized chromosomes and either unseparated or closely juxtaposed spindle pole bodies. (B) Overexpression of ESP1 during meiosis reduces chromosome arm-associated cohesin in condensin mutant ycs4-2. Using these criteria.to medium-sized spindles (w2 m) have formed (Figures 3A and 3E and see below). Sumara et al. 2000).. Thus. Similarly. 2000. One potential problem with this conclusion is that cells have the same morphology at metaphase I and just after anaphase I onset when cohesin is known to be removed by separase. In metaphase I cells. As a guide. To address further the timing of cohesin removal.. and 3G). An HA antibody was used to detected HA-tagged proteins. REC8.. or SMC1. the intensity of chromosome bound Rec8 in metaphase I cells is reduced compared to prophase I cells (Figure 3A). (A) Localization of cohesin subunit Rec8 in post-anaphase I cells. At least 100 cells were scored for each strain. and an α-tubulin antibody was used to detect the microtubule spindle. Error bars show the standard error. we used chromatin immunoprecipitation (ChIP) to assess the chro- . in ycs4-2 and ycg1-2 cells Rec8 remains associated throughout the chromosomes when chromosome bridging occurs. we first tested whether meiotic cohesin can be removed prior to anaphase I. a subset of cohesin appears to be removed from chromosomes between prophase I and metaphase I. Using the same criteria to distinguish cells at prophase I or metaphase I. Therefore. (C) Quantitation of paired GFP spots from telomeres of chromosome V homologs as shown in Figure 1D. Condensin Is Required for Cohesin Removal Prior to Anaphase I Having shown that condensin is required for the removal of cohesin from chromosome arms in MI. we addressed when condensin is needed to facilitate cohesin removal. and short. To test the validity of this conclusion. Rec8 is only associated with the portion of chromosomes proximal to the spindle poles. In wt cells.. To follow chromosome-associated cohesin. from these analyses of both normal and metaphase-arrested meiotic cells. nuclear spreads were prepared from meiotic cells with the epitope-tagged alleles of the cohesin subunits.
Cells with spindle length w2 m were counted as metaphase I cells (Meta. Error bars show the standard error. CARC7 (Figure 4A). (B) Representative images showing chromosome localization of Rec8 in YCS4 PCLB2CDC20 and ycs4-2 PCLB2CDC20. CEN3. (G) Quantitation of Scc3 intensity as done for Rec8 (see [C] and [D]). while w95% of cells are arrested at metaphase I by 11 hr after induction of meiosis (data not shown). C. n > 50. the majority of cells are at prophase I by 6 hr after induction of meiosis. I). During synchronous meiosis of Cdc20-depleted cells. (A) Representative images showing chromosome localization of Rec8. These strains were induced for meiosis at 30°C for 8 hr (A and E) or at 23°C for 1 hr and shifted to 34°C for 7 hr (B. Cells at pachytene were used as prophase I cells (Pro. The two cells shown were acquired from the same microcopy field. Note that these meiotic cells are unable to progress beyond metaphase I as a result of Cdc20 depletion. Two cells shown were acquired from the same microcopy field. Cohesin Removal Prior to Anaphase I Meiotic nuclei spreads were prepared from strains with either Rec8 (A–D) or Scc3 (E–G) tagged with 3×HA and processed for indirect immunofluorescence. Note that the intensity of Rec8 at prophase I is similar among different strains.Condensin Mediates Cohesin Removal 401 Figure 3. ChIP allowed us to evaluate a much larger population of cells. Error bars show the standard error. The upper cell is at prophase I. . While immunofluorescence allowed us to focus on individual cells. I). We analyzed two representative cohesinassociated regions. (C) Quantitation of Rec8 intensity with respect to cell stage based on morphologies of chromosome and spindle (see text for details). the lower one is at metaphase I. (D) Percent of Rec8 that is removed prior to anaphase I (1 − (average intensity of metaphase cell divided by average intensity of prophase cell)). At both sites. mosome association of cohesin. Diagram shows the fraction of Scc3 that is removed prior to anaphase I. F. The top panel shows the average absolute intensity of Rec8 staining per cell (n > 50). a centromere site. (F) Representative images showing chromosome localization of Scc3 in YCS4 PCLB2CDC20 and ycs4-2 PCLB2CDC20. and a chromosome arm site. (E) Representative images showing chromosome localization of Scc3. and G).
. We used indirect immunofluorescence to monitor chromatin bound cohesin in prophase I and metaphase I cells in which either Cdc5 or Ipl1 was depleted during meiosis (Figure 5). the immunofluorescence and ChIP analyses show that condensin is required for removal of a subset of cohesin between prophase I and metaphase I. (D) Rec8 ChIP profile at CEN3 in ycs4-2 PCLB2CDC20 cells. Rec8 removal prior to anaphase I is completely inhibited (Figure 5A. (A) A schematic representation of the position of CEN3 and CARC7 on chromosome III. we asked whether cohesin removal prior to anaphase I require either Cdc5 (Polo). we analyzed chromatin bound cohesin in meiotic ycs4-2 cells in which Ycs4 function was inactivated. yeastgenome. One obvious candidate is the separase. raised to the nonpermissive temperature to inactivate esp1-1.. Ipl1 (Aurora). 2002. Taken together. and in budding yeast to be hyperphosphorylated by Cdc5 (Rogers et al. In Cdc5-depleted cells. our unpublished data). 2003. lower panels). or both. 2003. we compared Rec8 phosphorylation in wild-type. 2003. Using the same immunofluorescence and ChIP methods. Lee and Amon. AIR-2. Clyne et al. Both Rec8 and Scc3 are localized along the entire length of the chromosomes at metaphase I in ycs4-2. is critical for cohesin removal prior to anaphase I. Therefore.Cell 402 Figure 4. the cohesin binding pattern as determined by ChIP at CEN3 and CARC7 does not change significantly between prophase I and metaphase I in ycs4-2 cells (Figures 4D and 4E). we needed a substrate to monitor the activity of these kinases. 2002. 2003). Cdc5 Is Required for Cohesin Removal Prior to Anaphase I We reasoned that condensin may mediate cohesin removal from chromosomes by influencing established regulators of cohesin removal. (C) Rec8 ChIP profile at CARC7 in PCLB2 CDC20 cells. Cdc5. This strain was induced to undergo meiosis. The inhibition of cohesin removal is also observed in ycg1-2 (our unpublished data). Having established that meiotic cohesin is removed prior to anaphase I. (E) Rec8 ChIP profile at CARC7 in ycs4-2 PCLB2CDC20 cells. Cdc5 or Ipl1 protein was not detectable 2 hr after induction of meiosis. the chromosome association of Rec8 decreases w2fold between prophase I and metaphase I (Figures 4B and 4C). Lee and Amon. we constructed an esp1-1 PCLB2CDC20 strain. To assess the usefulness of Rec8 as a substrate. elegans to be phosphorylated by an Ipl1 ortholog. Two other potential regulators of condensin-dependent cohesin removal are the Aurora B and Polo-like kinases since both have been shown to have defects in cohesin removal in meiosis (Rogers et al. Thus. Rec8 removal occurs albeit less efficiently (Figure 5A. The y axis shows the percent of input chromatin in Rec8 ChIP. we postulated that condensin might influence either directly or indirectly these kinases to regulate cohesin removal.. Consistent with the immunofluorescence data. while in Ipl1-depleted cells. Esp1. Cdc5- .org) coordinates of chromosome III are shown at the x axis in (B)–(E). Clyne et al. nor at any time thereafter (Lee and Amon. Condensin Promotes the Ability of Cdc5 to Localize to Chromosomes and to Phosphorylate the Cohesin Subunit Rec8 Having implicated Cdc5 and Ipl1 in cohesin removal. and the total intensity of chromosomal Rec8 and Scc3 is similar between prophase I and metaphase I in ycs4-2 (Figures 3D and 3G).. upper panels). Rec8 removal prior to anaphase I was unaffected in this strain (Figures 3C and 3D). both by indirect immunofluorescence and ChIP. and then ana- lyzed for chromosome bound cohesin in prophase I and metaphase I as described above. suggesting that condensin-dependent removal of cohesin at this stage is independent of Esp1.. SGD (Saccharomyces Genome Database: http://www. In order to address this question. To test this hypothesis. we next addressed if condensin is required for this phase of cohesin removal. 2003). ChIP was performed on cells enriched for prophase I (6 hr) and metaphase I (11 hr) (see Experimental Procedures). we next addressed whether condensin might be required for Cdc5 and Ipl1 activity. previous studies of ESP1 mutant cells showed that they are defective for cohesin removal at the anaphase I onset (Buonomo et al. Chromatin Immunoprecipitation Analysis of Rec8 Association at CEN3 and CARC7 Wild-type and ycs4-2 cells were induced for meiosis at 23°C for 1 hr and shifted to 34°C. Thus. (B) Rec8 ChIP profile at CEN3 in PCLB2 CDC20 cells. Indeed. we show that a subset of cohesin is removed prior to anaphase I. To test whether cohesin removal prior to anaphase I onset is also dependent on Esp1 function. lower panels). Depletion of Cdc5 and Ipl1 was confirmed by immunoblotting analysis. 2000). in agreement with the value obtained by cytological analysis (Figures 3C and 3D). and Ipl1 to a lesser extent. Rec8 had been shown in C. essentially no different from prophase I (Figures 3B and 3F.
indicating a small reduction in Rec8 phosphorylation. In Cdc5-depleted cells. the pixel values of spindle pole body-associated Cdc5 were subtracted from that of total chromosome-associated Cdc5 (see Experimental Procedures). The different levels of Rec8 hyperphosphorylation in wildtype. Nuclei spread was prepared and subjected to indirect immunofluorescence as shown in Figure 3. and Ipl1-depleted cells (Figure 6A). Error bars show the standard error. More than 50 metaphase I cells were measured in PCLB2CDC20 and ycg1-2 PCLB2CDC20. depleted. the upper band of the doublet disappears. Diagram shows the percent of Rec8 that is removed prior to anaphase I. hy- . (D) Quantitation of Rec8 intensity with respect to cell stage based on morphologies of chromosome and spindle as described in Figure 3C. Figure 6. Cdc5 binds to spindle pole bodies as well. suggesting that this phosphorylation may be relevant to cohesin removal. Cultures were induced for meiosis at 23°C for 1 hr and shifted to 34°C for 11 hr. In metaphase I of condensin mutants ycs4-2 and ycg1-2. the two bands in the doublet are of similar intensity. (B) Quantitation of Rec8 intensity in cells from PCLB2CDC5 PCLB2 CDC20 and PCLB2IPL1 PCLB2CDC20 (see legend Figures 3C and 3D). Note that. Condensin Regulates Rec8 Phosphorylation and Cdc5 Chromosome Localization (A) Immunoblot showing Rec8 hyperphosphorylation in arrested metaphase I cells. Thus. Using Rec8 hyperphosphorylation as a reporter for Cdc5 activity. and Cdc5-depleted cells correlates with the percent removal of cohesin between prophase I and metaphase I (Figure 5B). (A) Representative images showing chromosome localization of Rec8 in meiotic cells depleted for Cdc5 (PCLB2CDC5 PCLB2CDC20) or Ipl1 (PCLB2IPL1 PCLB2CDC20). (E) Quantitation of paired GFP spots from chromosome V homologs as described in Figure 1D. The first lane shows a “wild-type” (PCLB2CDC20) sample treated with calf intestine alkaline phosphatase (CIP). Error bars show the standard error. with the upper one referring to the hyperphosphorylated band. Meiotic spreads were performed on strains with Cdc5 tagged with 3×HA and followed by indirect immunofluorescence. (C) Quantitative analysis of chromosome localization of Cdc5 in wild-type and ycg1-2 cells arrested at metaphase I as a result of Cdc20 depletion. (B) Representative images showing chromosome association of Cdc5 in wild-type and ycg1-2 cells with a metaphase I spindle. we asked whether this hyperphosphorylation was affected in condensin mutants. Protein extracts were prepared for immunoblotting. The arrows indicate phosphorylated forms of Rec8. in addition of chromosome localization. Rec8 migrates as a hyperphosphorylated doublet with the majority in the slower migrating form. In wildtype cells. To acquire the net pixel intensity of chromosomeassociated Cdc5. In Ipl1-depleted cells. Cultures were induced for meiosis by a similar scheme as shown in (A). Cdc5 Is Required for Cohesin Removal Prior to Anaphase I Yeast strains were induced to enter meiosis at 30°C.Condensin Mediates Cohesin Removal 403 Figure 5. Cdc5 is required for the hyperphosphorylation of cohesin. as expected from previous results while Ipl1 has a minor role. Ipl1-depeleted.
The ability of cohesin to influence condensin-mediated condensation has also been observed in Sordaria but not all eukaryotes (van Heemst et al.. and cohesins need to be removed to allow condensins to help mediate condensation.. we have been unable to detect a Cdc5-dependent mobility shift for yeast Scc3 (our unpublished data).. In wild-type cells. cohesin may serve as a scaffold to regulate a condensin-dependent function in meiosis. which were identified initially through independent studies of cohesion and condensation. the vertebrate ortholog of Scc3. 2004). However.5 × 103 with a t test p value less than 0. raising the possibility that this particular interaction between distinct SMC complexes might be the exception rather than the rule. indicating that the difference is statistically significant. suggesting a possible mechanism for how condensin might regulate Cdc5 to promote cohesin removal. 2002.5 × 104.. in ycg1-2 cells at nonpermissive temperature. there is an approximately 2-fold reduction of chromosome-associated Cdc5 in ycg1-2 cells at metaphase I. Cdc5 phosphorylates cohesin preferentially in the context of the chromatin during mitosis (Hornig and Uhlmann. Unal et al. By coupling condensin to cohesin removal. Cdc5 association with the chromosomes. This difference in chromosome association was not the result of change in CDC5 expression because Cdc5 was detected at a similar level in wild-type and ycg1-2 (data not shown). we wanted to test whether the activation of Cdc5 by condensin is important to remove cohesin. Cdc5 phosphorylation of SA2. almost to the level observed in Cdc5-depleted cells (Figure 6A). observations in other studies suggest that condensin-mediated removal of cohesin may be conserved in meiosis and mitosis among diverse eukaryotes (see below). Interestingly.. the relevant target of Cdc5 for cohesin removal may be another cohesin subunit. analogous to its proposed function in regulating mitotic rDNA condensation in budding yeast (Guacci et al. Discussion In this study we show that condensin facilitates the removal of cohesin from chromosomes during the first meiotic division of budding yeast and that this removal is important to dissolve the links between homologs that ensure proper homolog segregation. cohesin is needed to regulate condensin so that condensin can properly fold the w1 Mb rDNA locus. Condensin may promote Cdc5 binding to chromosomes. while in ycg1-2.7 × 103. Lavoie et al. However. The first indication for an interaction between these two SMC complexes came from studies in budding yeast (Guacci et al. the condensindependent removal of cohesin in meiosis reflects an emerging theme in which different SMC complexes interact to ensure proper chromosome dynamics. the presence of cohesins does not seem to impair mitotic chromosome condensation (Losada et al. then increasing the level of Cdc5 in meiosis might restore Cdc5 activity in condensin mutants and promote cohesin removal and the dissolution of homolog pairing. Lavoie et al. but not ycg1-2. These data support the conclusion that condensin activation of Cdc5 during meiosis is important for cohesin removal and the dissolution of homolog linkage. This similar reduction in Rec8 phosphorylation in condensin and Cdc5-depleted cells correlates with their similar defect in cohesin removal (Figures 3D and 5B).. the MRX complex (an SMC-like complex) is required for recruiting cohesin to the double-strand break site in both yeast and human cells (Kim et al. two different SMC complexes. 2005). To validate the difference in chromosome association of Cdc5 between wild-type and ycg1-2. In addition. 2002). rather than Scc1 (mitotic copy of Rec8) is essential for prophase removal (Hauf et al. Thus. is significantly perturbed (Figure 6B).. the value is only 8. Therefore. Having shown that condensin is important for proper chromosome localization and optimal activity of Cdc5. These results are consistent with the conclusion that condensin directly or indirectly activates Cdc5. On average. but not with the spindle pole bodies. We reasoned if this was so. condensin facilitates Cdc5 association with the chromosomes. This observation provides a striking example of a functional connection between cohesin and condensin. cohesin removal prior to anaphase I is restored to approximately half of that of wildtype (Figure 6D). 2002). 2004). However. the average pixel intensity of chromosome-associated Cdc5 per nucleus is 1. at permissive temperature). Furthermore. Vagnarelli et al.. 1999. our observation that condensin mediates cohesin removal in meiosis provides significant additional support for a tie between these two complexes. 2004). the cell ensures that the cohesin scaffold is not removed until after condensin . In ycs4-2 PDMC1CDC5 cells. 1997. In wild-type cells with metaphase I spindles. which is important for cohesin removal between prophase I and metaphase I. Cdc5 associates with chromosomes as well as with the spindle pole bodies in spread nuclei (Figure 6B). In a recent study of mitotic HeLa cells.Cell 404 perphosphorylation of Rec8 is significantly reduced. To address whether condensin promotes chromosome association of Cdc5. Furthermore. The standard error for these two values is 0. we arrested these different cell types at metaphase I by Cdc20 depletion and quantified Cdc5 association with the chromosomes (Figure 6C). In contrast. Therefore. To increase Cdc5 meiotic level. and this chromatin bound Cdc5 may be more proficient at cohesin phosphorylation. 1997.001. While Rec8 is a valuable readout to show that condensin modulates Cdc5 activity. This observation suggests a possible mechanism for how condensin stimulates Cdc5 to phosphorylate cohesin in meiosis. Why does the cell couple condensin function to loss of cohesion in meiosis? One possibility is that cohesins are inhibitors for condensation.. Alternatively. In budding yeast. Scc3 does not contain the phosphorylated region of SA2 that is necessary for cohesin removal.. we replaced the endogenous promoter of CDC5 with the promoter for DMC1 on one of the two homologs. we observed a 3-fold increase in homolog resolution as assayed by the separation of telomeres from chromosome V homologs (Figure 6E). we generated strains with a functional allele of Cdc5 tagged with the HA epitope (note that this tagged CDC5 allele is synthetically lethal with ycs4-2. 2002). additional experimentation is required for unambiguous identification of the relevant target(s).
chromosomes are condensed (about 2-fold in budding yeast). in condensin mutant cells. We speculate that in meiosis. the Polo-like kinase in yeast. 2002. we have been unable to detect this interaction by immunoprecipitation in soluble extracts. Second. Marston et al. However. Therefore. Hirota et al.. 2004). From our analyses in yeast. While condensin is required for the proper formation of axial element. In many metazoans. has completed its function. 2001.. Condensin activates Polo-like kinase (Cdc5) potentially through recruitment of the kinase to the chromosomes. Since Cdc5 regulates many cell cycle events. Condensin is also required for chromosome compaction and individualization. Interestingly. Prieto et al. The condensin/Cdc5 pathway for cohesin removal in prophase is likely to exist during meiosis in other organisms. Second. 2004). Cohesin removal occurs in Xenopus egg extracts depleted for condensin but is impaired in HeLa cells depleted for the canonical condensin complex by RNAi (Losada et al. 2001. the activation of Cdc5 by condensin may provide an important tool to pursue the connection between chromosome structure and recombination. remaining cohesin on the chromosome arms is removed when it is cleaved by separase. which activates separase.. 2003. In this light. followed by condensin (blue dots) loading in prophase I. Cdc5 and condensin are needed for cohesin removal prior to anaphase I.. 2002). the anaphase promoting complex. cohesin must be removed by a separase-independent pathway. the role of condensin in this pathway has been controversial.. The mechanism for condensin activation of Cdc5 remains to be elucidated... Alternatively.. changes in chromosome structure have been proposed as a mechanism to resolve meiotic recombinants (Kleckner et al. Since homolog segregation requires inactivation of sister chromatid cohesion. in Xenopus oocytes. leading to cohesin dissociation from the chromosomes prior to anaphase I. And fourth. but it is reorganized and appears less intense on bivalents at metaphase I (Pasierbek et al. condensin may activate Cdc5 indirectly through condensin’s function in meiotic chromosome structure. Furthermore. chromosome bound cohesin appears to be diminished prior to activation of separase at the onset of anaphase I.. Sumara et al.. 2001. However. 2003). these apparently contradicting results can be reconciled simply if Xenopus eggs are stockpiled with an excess of Cdc5 such that Cdc5 activation by condensin is not needed. 2005).. Consistent with this hypothesis. Black ovals represent centromeres. This similarity between MEI-S332 and condensin is intriguing since both help generate the unique pattern of . condensin and Cdc5 are both required for a hyperphosphorylation of cohesin subunit Rec8. Third. 2004). cohesin removal is ameliorated by increased level of Cdc5. 1995. Thus. Four lines of evidence from this study support the conclusion that condensin regulates cohesin removal between prophase I and metaphase I in yeast by modulating the activity of Cdc5. Summary of Cohesin Removal during Meiosis I Cohesin (shown as red dots) is loaded onto meiotic chromosomes during S phase. 2002. 2004). but in mitosis the Cdc5 and by inference condensin-dependent removal of cohesin is not required for sister chromatid segregation (Hauf et al. is dispensable for homolog segregation (Peter et al. Lee et al. analysis of a red1 mutant reveals that axial element assembly is not required for proper cohesin removal prior to or after anaphase I (our unpublished data). In mi- totic prophase. Cdc5 also preferentially phosphorylates chromatin bound cohesin because it is recruited to the chromosome through condensin (Figure 7). condensin mutants do cause transient delays in mitotic and meiotic cell cycle progression in a number of organisms (Yu and Koshland. It is interesting to note that the protection of centromeric cohesin by the MEI-S332 (Sgo1) family of proteins is also essential for meiosis but not mitosis in yeast and fly (Kerrebrock et al.. The condensin-dependent removal of cohesin is required for efficient homolog segregation in meiosis (this study). Taieb et al. The notion that the transition between different structures of a chromosome is regulated by a feedback between structural complexes is analogous to paradigms in phage morphogenesis and metabolic pathways. Revenkova et al.Condensin Mediates Cohesin Removal 405 Figure 7.. At the onset of anaphase I.. condensin is required for the proper chromosomal localization of Cdc5. Hirota et al. Polo-like kinase modifies cohesin or cohesin-associated factor. a Cdc5 pathway for separase-independent removal of cohesin has also been described (Losada et al. the control of Cdc5 by condensin provides a means to coordinate the assembly and disassembly of chromosome structures with other cell cycle events.. cohesin is localized along the entire length of the chromosomes at pachytene. 2004). 2001. Cdc5 can phosphorylate cohesin subunits in vitro and preferentially phosphorylates chromatin-associated cohesin in mitosis (Hornig and Uhlmann. we suggest that cohesin removal between prophase and metaphase by condensin activation of Polo kinase is likely to be conserved in both mitosis and meiosis of most eukaryotes. One possibility is that condensin directly binds to Cdc5. First. 2001). Subsequently. although it may occur only on chromatins.
Loidl.. After 1 hr induction of meiosis at 23°C. Koshland. 14.. Fuchs. which is in the linear range of the camera. 167. samples (equivalent to 500 l protein extract) were treated with 5 units of calf intestine alkaline phosphatase (Roche) at 37°C for 15 min. Cha. Displayed images were processed with IP-Lab for contrast adjustment and pseudocoloring. Progression of meiotic DNA replication is modulated by interchromosomal interaction proteins.. Lichten.. To remove the phosphate groups of Rec8. 2005 Revised: July 25...S.. V. B. negatively by Spo11p and positively by Rec8p. 47–57.K. Dittrich. M. Acknowledgments We thank A. Yanowitz. 387–398. E.. S.F. I. R. J. J. 455–469. D. Kock. A semiquantitative PCR method was used to analyze cohesin association at centromere 3 and CARC7 (Laloraya et al. Mistrot. and the resulting segments were used to acquire Cdc5 intensity..L. 613–625.. A conditional allele of IPL1 (PCLB2IPL1) was generated by replacing the endogenous IPL1 promoter with the promoter for CLB2 (w1 Kb upstream of CLB2). Disjunction of homologous chromosomes in meiosis I depends on proteolytic cleavage of the meiotic cohesin Rec8 by separin. The HA antibody (12CA5.. Stegmeier. Cdc14 and condensin control the dissolution of cohesin-independent chromosome linkages at repeated DNA. Lichten. Katis. (2000). In meiosis.. ChIP procedures were followed as before (Glynn et al. 2000).. Cell 91. J. One possibility is that the condensin/Cdc5 pathway for removal of cohesin is only important in meiosis because of constraints of MI and MII and the complex stepwise removal of cohesin needed to achieve both homolog and sister chromatid segregation. R. S. Received: April 6. Clyne. K. Fluorescence images were acquired with a Zeiss Axioplans 2 microscope (100× objectives.B. These segments were transferred to corresponding image windows to acquire net intensities of immunofluorescence with measurement tools in IP-Lab. 493–503... K. while the temperature-sensitive strains (ycs4-2. 10. Segments of spread nuclei were created upon DAPI-stained chromosomes. Uhlmann. and esp1-1. (2004). Nuclei Spread and Immunofluorescence Yeast meiotic spread and antibody incubation were performed essentially as described previously (Yu and Koshland. Koshland. Heidinger. ycg1-2 and esp1-1) are congenic to SK1.. Genes Dev. the DMC1 promoter (421bp upstream of DMC1) was used to replace the endogenous promoter of ESP1 or CDC5 on one of the homologs.. This work was supported by HHMI to D.Cell 406 cohesin binding to chromosomes in MI (present at centromeres but lost on arms) that allows homologs which have undergone recombination to resolve without compromising sister chromatid cohesion. Murphy assisted image analysis. D.C. binary segments made for the spindle pole bodies were subtracted from those of DAPI-stained chromosomes. 2003).40) equipped with a Quantix CCD camera (Photometrics). e259. but in those cells where recombination occurs. Nat. and Strunnikov. NA = 1. 2005 References Buonomo. or 63× objectives. since all chromosomes must undergo recombination. Condensin restructures chromosomes in preparation for meiotic divisions. Synchronous cultures were induced for meiosis as described previously (Yu and Koshland.K. H. the separase pathway normally suffices for cohesin removal because recombination is rare. To overexpress ESP1 or CDC5 during meiosis. 2003). C.. and Amon. and Meyer. Herskowitz.pbio.K. Cell Biol. Severson. To obtain the net intensity of chromosome-associated Cdc5. B. PLoS Biol.E.. DeRisi. In mitosis. Genome-wide mapping of the cohesin complex in the yeast Saccharomyces cerevisiae. A. (2003). Hauf. Cell Biol. and Pe- . (2004).-G. Cell 117. Roitinger.. The average intensity of cohesin staining at prophase I was arbitrarily defined as 100% (Figures 3C. cells were arrested at metaphase I (w95%) as a result of Cdc20 depletion (data not shown). 480–485. A PCR-based strategy was used to tag 3×HA to C termini of CDC5 and SCC3 (Schneider et al. the condensin/Cdc5 pathway is essential to remove cohesins to allow homolog segregation. Cell 103. R. After 10–12 hr.30. E. and Nasmyth. Guacci. Keeney.. E. Glynn. 2004). (2000).com/cgi/content/full/123/3/397/ DC1/.L. Supplemental Data Supplemental Data include five figures and can be found with this article online at http://www.. Yu.. Chromatin Immunoprecipitation Synchronous cultures (100 ml) induced for meiosis were withdrawn at 6 and 11 hr of sporulation at 34°C and fixed with 1% formaldehyde at 34°C for 2 hr (Figure 4). the presence of this pathway in mitosis is tolerated because it is not detrimental. cerevisiae. B. (2004). J. the majority of cells were at prophase I. NA = 1. Alternatively. LacI-GFP was placed at the LEU2 locus.M.C. which is nonpermissive for ycs4-2. Chromosome V was marked with GFP using the TetO/TetR system as before (Yu and Koshland. C. 2 × 224 LacO repeats were inserted at three designated regions on chromosome IV: TRP1 (w12 kb to the right of CEN4).R. Roche) was used at 1 g/ml for 2 hr at room temperature. 2. 5B. Unal. Amon for communicating unpublished results and sharing reagents. and Y.. Megee. 5. Chan. 3D. LYS4 (w482 kb to the right of CEN4). The α-tubulin antibody (YOL1/34. Secondary antibodies (goat anti-mouse and goat anti-rat) were used at a dilution of 1:500. M. cultures were shifted to 34°C.. R. Experimental Procedures Yeast Strains and Cultures Yeast strains used in this study are diploids isogenic to SK1. A.. Benjamin. A direct link between sister chromatid cohesion and chromosome condensation revealed through the analysis of MCD1 in S. Hoang. E. Jessop. Clyne. 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