The asymmetry of female meiosis reduces the frequency of inheritance of unpaired chromosomes
- University of California, Davis, United States
- University of Calgary, Canada
Figures
Figure 1
Trisomy correction during meiosis I.
(A) Illustration showing expected outcomes of female meiosis in XXX wild-type worms, assuming the extra univalent X (red) does not lose cohesion (yellow) between sister chromatids during anaphase I …
Figure 2 with 1 supplement
X univalents are preferentially lost between metaphase I and metaphase II in him-8 mutants.
Z projections of living (A–E) and fixed (F–J) C. elegans meiotic embryos viewed down the pole-to-pole spindle axis at metaphase I (A, B, F, G) or metaphase II (C, D, E, H, I, J). mCherry::Histone …
Figure 2—figure supplement 1
zim-2 embryos also deposit unpaired chromosome V univalents into the first polar body.
Z projections of fixed meiotic embryos viewed down the pole-to-pole spindle axis. Embryos were stained with DAPI, anti-tubulin antibody, and a LacO FISH probe that recognizes a LacO array integrated …
Figure 3 with 2 supplements
X univalents biorient at metaphase I in him-8 embryos.
(A) Cartoon diagram of REC-8 staining on bivalents and univalents. (B and C) Anti-REC-8 staining of metaphase I and metaphase II embryos with bivalents (yellow arrow head) and univalents (white …
Figure 3—figure supplement 1
Imaging of GFP::KNL-2 demonstrates that him-8 univalent chromosomes biorient at metaphase of meiosis I.
(A–B) Z-projections through fixed GFP::KNL-2 embryos stained with DAPI and anti-tubulin antibody. (A) Metaphase I wild-type and him-8 embryos showing the distinct KNL-2 cups around bivalents (yellow …
Figure 3—figure supplement 2
Reduced levels of AIR-2 are loaded on him-8 X univalents at meiosis I.
(A and B) Z projections of fixed metaphase I, GFP:AIR-2 embryos stained with DAPI and anti-tubulin antibody. AIR-2 is loaded between homologs of both wild-type (A) and him-8 bivalents (B), whereas …
Figure 4
X univalents lag at anaphase I.
(A) Time-lapse images of a living wild-type embryo undergoing anaphase I show chromosomes separating as two distinct masses. (B) Time-lapse images of a living him-8 embryo show a lagging chromosome …
Figure 5
The contractile ring moves inward past the lagging chromosomes of him-8 embryos.
(A) Time-lapse sequence of anaphase I in a him-8 strain with GFP::PH, GFP::Tubulin, and mCherry::Histone H2B. The plasma membrane ingresses past the lagging chromosomes to engulf them in the polar …
Figure 6
Lagging chromosomes are captured by the septin tube and expelled with polar bodies.
Time-lapse imaging of embryos expressing GFP::septin and mCherry::histone. (A) Time-lapse images of a living wild-type embryo undergoing anaphase I show the conversion of a flat washer–shaped …
Figure 7
Early bias of univalent X chromosomes might occur at the metaphase to anaphase I transition.
Representative cartoon diagrams and Z projections from fixed embryos stained with DAPI, anti-tubulin antibody, and LacO(X) FISH probe. Cortex is at the top. (A–C) Both X univalents on metaphase I …
Tables
Table 1
Enhancement of the segregation bias in him-8 mutants by mutations in the myosin phosphatase, mel-11
| Self-progeny counts | |||||
|---|---|---|---|---|---|
| Genotype | Temperature (°C) | % XO male | % XX hermaphrodite | % XXX Dpy | Total progeny |
| mel-11(sb55) unc-4 | 20 | 0.2 | 99.8 | NC | 1763 |
| mel-11(sb55) unc-4; him-8 | 20 | 49* | 51 | NC | 374 |
| unc-4; him-8 | 20 | 34 | 66 | NC | 1442 |
| mel-11(it126) unc-4 | 15 | 0.6 | 99 | NC | 790 |
| mel-11(it126) unc-4; him-8 | 15 | 58* | 38.6 | 3.4 | 873 |
| Ratio of nulloX ova/diploX ova calculated from progeny of cross with lon-2 males | |||||
|---|---|---|---|---|---|
| Maternal genotype | Temperature (°C) | # NulloX (ion male progeny) | # DiploX (dpy progeny) | Nullo/diplo | Total progeny |
| mel-11(it26) unc-4 | 25 | 1 | 0 | NA | 785 |
| mel-11(it26) unc-4; him-8 | 25 | 160 | 7 | 22.9 | 595 |
| unc-4; him-8 | 25 | 98 | 31 | 3.2 | 677 |
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mel-11 increases the frequency of male progeny from him-8 mothers. mel-11(sb55) and mel-11(it26) worms produce high frequencies of dead embryos, which cannot be scored for sex at 25°C (Wissmann et al., 1999). Percent male (XO), hermaphrodite (XX), and dumpy (XXX) progeny from self-fertilizing mel-11, him-8, or him-8 mel-11 double mutant worms were therefore scored at 15°C and 20°C. Only progeny that developed to the L4 or adult stage were counted. *Two-tailed p < 0.0001 by binomial test compared with him-8 alone. 100% of mel-11(it26) self progeny die as embryos at 25°C, but this lethality is rescued by mel-11(+) sperm (Kemphues et al., 1988). The progeny of mel-11(it26) hermaphrodites crossed with lon-2 males could therefore be scored at 25°C. When lon-2(+) hermaphrodites are crossed with lon-2 males (lon-2 is a recessive X-linked marker), 50% of the ova will be fertilized by sperm with a single lon-2 X chromosome. Fertilization of a nulloX ova by a lon-2 X sperm will result in a lon-2 male. Fertilization of a diploX ova by a lon-2 X sperm will result in a XXX dumpy worm. Random segregation of the unpaired X chromosomes in him-8 would result in a ratio of nulloX/diplo X ova of 1.0. The mel-11; him-8 double mutant showed a sevenfold increase in the ratio of nullo/diploX ova relative to him-8 alone, indicating an increased efficiency of eliminating maternal unpaired X chromosomes.
Additional files
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Supplementary file 1
C. elegans strains used in this study.
- https://doi.org/10.7554/eLife.06056.014
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Supplementary file 2
Z-stack of XC FISH on XXX wild-type metaphase plate in meiosis I. 16-bit 3-channel TIFF can be opened using FIJI or basic ImageJ (http://fiji.sc/Downloads). Data shown are a z-stack acquired with 300 nm steps through a meiosis I metaphase spindle. Chromosomes are shown in blue (DAPI), tubulin antibodies label the spindle in green, and the XC FISH probe labels X chromosomes (2 present) in red. Channels can be split for individual analysis using the channel splitter (Image > Colors > Split channels) or can be hidden using the channels tool (Image > Colors > Channels tool).
- https://doi.org/10.7554/eLife.06056.015
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Supplementary file 3
Z-stack of XC FISH on XXX wild-type metaphase plate in meiosis II. 16-bit 3-channel TIFF can be opened using FIJI or basic ImageJ (http://fiji.sc/Downloads). Data shown are a z-stack acquired with 300 nm steps through a meiosis II metaphase spindle. Chromosomes and the first polar body, which is on the top, are shown in blue (DAPI), tubulin antibodies label the spindle in green, and the XC FISH probe labels X chromosomes (1 present on the spindle) in red. Channels can be split for individual analysis using the channel splitter (Image > Colors > Split channels) or can be hidden using the channels tool (Image > Colors > Channels tool).
- https://doi.org/10.7554/eLife.06056.016
