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First published online 11 March 2003
doi: 10.1242/jcs.00387

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Linear element formation and their role in meiotic sister chromatid cohesion and chromosome pairing

¹ CREST Research Project, Kansai Advanced Research Center, Communications Research Laboratory, Kobe 651-2492, Japan
² Institute of Cell Biology, University of Bern, CH-3012 Bern, Switzerland

View larger version (16K): [in a new window]   Fig. 7. Meiotic sister chromatid cohesion and chromosome segregation in the rec10, rec8 and rec11 mutants. (A-D) Sister chromatid cohesion in meiotic prophase at different loci. Heterozygous crosses were carried out with GFP-labeled strains, and the numbers of GFP signals were determined in living cells as described in Materials and Methods. 50 horse-tail nuclei were examined in each experiment. (A) Sister chromatid cohesion at the cen2 locus. GFP labeled h- control (AY261-1C), rec10 (95), rec8 (101) and rec11 (100) strains were crossed to unlabeled h+ control (L975), rec10 (67), rec8 (68-2710) and rec11 (70) strains, respectively. (B) Sister chromatid cohesion at the his2 locus. GFP labeled h- control (153), rec10 (156), rec8 (157) and rec11 (155) strains were crossed to unlabeled h+ strains. The same h+ strains were used as described for the cen2 locus. (C) Sister chromatid cohesion at the ade1 locus. GFP labeled h+ control (AY234-6B), rec10 (116), rec8 (143) and rec11 (117) strains were crossed to unlabeled h- control (105), rec10 (68), rec8 (128) and rec11 (132) strains, respectively. (D) Sister chromatid cohesion at the ade8 locus. GFP labeled h- control (AY 208-21A), rec10 (143), rec8 (142) and rec11 (146) strains were crossed to unlabeled h+ strains. The same h+ strains were used as described for the cen2 locus. (E) Evaluation of chromosomal mis-segregation in the rec10, rec8 and rec11 mutants. To assess PSSC (precocious sister chromatid separation), the same heterozygous crosses were carried out as described for the analysis of sister chromatid cohesion at the cen2 locus. NDJI (nondisjunction at the first division) was examined in strains bearing a homozygous GFP labeling at the cen2 locus. Control (CT2111-2); rec10 (119); rec8 (161); and rec11 (121). Cells having two nuclei were identified after Hoechst 33342 staining and the GFP signals were analyzed in 50 cells in each experiment. (F) A schematic representation of chromosome II with the positions of the GFP labeled loci along the right arm.

View larger version (95K): [in a new window]   Fig. 5. Meiotic time-course experiment in the rec11 mutant. The cohesion-defect phenotype of linear elements and the temporal comparison of cytological events were analyzed in a time-course of strain ED4. (A) Arrowheads point to very small linear elements in a class A nucleus of the rec11 mutant. Arrow shows the spindle pole body; `n' is the nucleolus. (B) Class B morphology seen in the rec11 mutant (nucleus on left-hand side) and in the rec8rec11 double deletion strain ED2 (right-hand side). Arrowheads point at aberrant linear elements. (C) Class C morphology seen in the rec11 mutant (nucleus on the left-hand side) and in the rec8rec11 double deletion strain ED2 (right-hand side). Arrowhead shows a linear element. Bar, 1 µm. (D) Quantitation of the different classes. (E) Meiotic time-course as followed by DAPI staining.

View larger version (80K): [in a new window]   Fig. 1. Linear element morphologies and temporal comparison of cytological events in a time-course of the JB6 control strain. (A-D) Electron micrographs of spread and silver-stained nuclei of different linear element morphologies. (A) Single, short elements in a class I nucleus. Arrowheads indicate linear elements; `n' is the nucleolus. (B) Developing network in a class IIa nucleus. The arrow points at the spindle pole body (SPB), which is located close to the nucleolus (n). (C) Bundle in a class IIb nucleus. (D) Single, long elements in a class III nucleus. Bar, 1 µm. (E) Quantitation and temporal order of the different morphological classes. (F) Timing of cytological events as followed by DAPI staining. Horse-tail nuclei indicate meiotic prophase. Cells with more than one nucleus have progressed through the first meiotic division. After meiotic induction cells undergo a final mitotic division (peak at 1 hour) before they enter meiosis from G1 phase.

View larger version (93K): [in a new window]   Fig. 2. Meiotic time-course experiment in the rec12 mutant. The morphologies of linear elements in spread and silver-stained nuclei and the timing of cytological events were analyzed in strain ED5. (A) Class I nucleus. Arrowheads show short linear elements; the arrow points to the spindle pole body; `n' indicates the nucleolus. (B) Class IIa nucleus with a network of elements. (C) Several short bundles in a class IIb nucleus. (D) Two class III nuclei showing an abundance of long elements. Bar, 1 µm. (E) Quantitation of the different classes of linear elements. (F) Timing of cytological events as followed by DAPI staining.

View larger version (94K): [in a new window]   Fig. 3. Meiotic time-course experiment in the rec14 mutant. Nuclear spreading and DAPI staining were carried out in a time-course of strain ED6. (A) Electron micrograph of a silver-stained class I nucleus. Arrowheads indicate short linear elements, the arrow points to the spindle pole body; `n' is the nucleolus. (B) Two class IIa nuclei. The nucleus on the left-hand side shows a regular network, the nucleus on the right-hand side has a `moth-eaten' network. (C) Short bundles in a class IIb nucleus. (D) Class III nucleus bearing single, long linear elements. Bar, 1 µm. (E) Quantitation of the different classes. (F) Timing of cytological events as followed by DAPI staining.

View larger version (113K): [in a new window]   Fig. 4. Meiotic time-course experiment in the meu13 mutant. The morphologies of linear elements and the temporal comparison of cytological events were analyzed in a time-course of strain ED8. (A) Electron micrograph of an early class IIb nucleus. Arrowheads indicate short bundles; the arrow points to the spindle pole body; `n' is the nucleolus. (B) Two class II nuclei representing networks. The nucleus on the right-hand side shows a transition of the network to the bundle phenotype. (C) Bundles in a late class IIb nucleus. (D) Class III nucleus with single, long elements. Bars, 1 µm. (E) Quantitation and temporal comparison of the different classes. (F) Meiotic time-course as followed by DAPI staining.

View larger version (41K): [in a new window]   Fig. 6. Meiotic time-course experiment in the rec10 mutant. (A) Empty meiotic nucleus. The chromatin region is faintly stained by silver nitrate; `n' indicates the more densely stained nucleolus. The arrow points to the spindle pole body which consists of a large and two small bodies. (B) A comparison of the timing of cytological events in the rec10 mutant ED3 and the control JB6 strain. Meiotic nuclei were identified in the electron microscope after spreading and silver staining. The horse-tail stage and the progression of meiotic divisions were analyzed in DAPI-stained cells.

View larger version (7K): [in a new window]   Fig. 8. Homologous chromosome pairing in the rec10 mutant relative to wild-type. To emphasize the pairing properties of the mutant, the persentage of homologous chromosome pairing in the different chromosomal regions in rec10 was expressed relative to that measured in the wild-type strain. (The original data are presented in Table 2.)