Live observation of fission yeast meiosis in recombination-deficient mutants
a study on achiasmate chromosome segregation
Monika Molnar1,
Jürg Bähler2,
Jürg Kohli1 and
Yasushi Hiraoka3
1
Institute of Cell Biology, University of Bern, CH-3012 Bern, Switzerland
2
The Sanger Centre, Wellcome Trust Genome Campus, Hinxton, Cambridge, CB10 1SA,
UK
3
CREST Research Project of the Japan Science and Technology Corporation, Kansai
Advanced Research Center, Communications Research Laboratory, Kobe 651-2492,
Japan
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Fig. 1. Prophase nuclear movements in wild-type, rec8 and rec7
mutant cells. Nuclei of strains (A) CRL 152 (wild type), (B) 57-2262
(rec8 mutant) and (C) 88-3485 (rec7 mutant) were stained
with Hoechst 33342. Images were taken in a single optical section with 2
minute intervals. Numbers on the left of each image indicate time in minutes.
In A, arrows indicate the position of the presumptive telomere cluster. In B,
arrows indicate the position of the leading edge of the nucleus. In C, arrows
indicate the position of the leading edge of the nucleus; the arrowhead points
at the presumptive telomere cluster. Scale bar: 10 µm.
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Fig. 2. Nuclear dynamics during the first meiotic division in the rec8 and
rec7 mutants. (A) rec8 mutant. Nuclei of strain 57-2262 were
stained with Hoechst 33342. Numbers on the right of the images indicate time
in minutes. (B,C) rec7 mutant. Nuclei of strain 88-3485 were stained
with Hoechst 33342, and two divisions with different outcome were chosen for
presentation. Numbers on the left of the images indicate time in minutes. In
case of division (B), chromosomes were apparently unevenly distributed between
the daughter nuclei. (C) Division resulted in even segregation. Equal numbers
of chromosomes moving to opposite poles are clearly discernable at 48 minutes.
The arrow indicates a chromosome moving between two poles. Scale bar: 10
µm.
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Fig. 3. Selected frames of the second meiotic division. Nuclei of strains CRL 152
(wild type), 57-2262 (rec8), and 88-3485 (rec7) were stained
with Hoechst 33342. Numbers on the right of the images indicate time in
minutes. Compare the even distribution of nuclear masses in the wild type
strain (A) with the irregular divisions seen in rec8 (B) and
rec7 (C). Scale bar: 10 µm.
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Fig. 4. GFP images of cen1 in a wild-type homothallic strain in meiosis I. Strain
AY 176-17D was induced to undergo meiosis and observed as described in
Materials and Methods. Numbers on the left of each image indicate time in
minutes. Scale bar: 10 µm.
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Fig. 5. GFP images of cen1 in a rec7 homothallic strain in meiosis I.
Meiosis was induced in strain A5, and the divisions were observed as described
in Materials and Methods. Numbers on the left of each image represent time in
minutes. (A) GFP signals arising from homologous chromosomes which eventually
moved to the same pole, resulting in nondisjunction I. The arrow points to the
chromosome moving to the same pole as its homolog. (B) Chromosome
re-orientation in rec7. The arrow points to the chromosome that moved
to the same pole as its homolog and subsequently re-oriented to the other
pole. Scale bar: 10 µm.
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Fig. 6. Precocious separation of sister chromatids in rec8. GFP images of
cen1 in the first meiotic division in rec8. Strains A4 and 68-2710
were crossed and observed as described in Materials and Methods. Numbers on
the left of each image indicate time in minutes. Note that only one of the
strains carries the GFP construct in this cross, thus the separating signals
arose from sister chromatids. Scale bar: 10 µm.
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Fig. 7. Spore numbers in rec+, rec8, rec7, rec14 and
rec15 zygotic asci. Strains CRL 152, 57-2262, 88-3485, A1 and A2 were
transferred onto sporulation medium and the spore numbers determined by phase
contrast microscopy in approximately 200 mature asci.
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Fig. 8. Ascus formation in recombination-deficient mutants. Morphologies of
rec+ (a), rec8 (b), rec7 (c),
rec14 (d) and rec15 (e) zygotic asci are shown after
visualization of the DNA content by DAPI staining (see Materials and Methods).
The same strains were used as in Fig. 8. In contrast to the uniform
distribution of nuclear masses in the spores of rec+ asci,
each mutant had spores with variable DNA content. Note the large spores in
rec7, rec14 and rec15 asci that enclosed more than one
DAPI-stainable body. Scale bar: 10 µm.
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© The Company of Biologists Ltd 2001
