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Telomere-independent homologue pairing and checkpoint escape of accessory ring chromosomes in male mouse meiosis.

Voet T, Liebe B, Labaere C, Marynen P, Scherthan H - J. Cell Biol. (2003)

Bottom Line: Fluorescent in situ hybridization and three-dimensional fluorescence microscopy revealed that ring MCs did not participate in meiotic telomere clustering while MC homologues paired at the XY-body periphery.Unaligned MCs triggered the spindle checkpoint leading to apoptosis of metaphase cells.Our findings indicate a telomere-independent mechanism for pairing of mammalian MCs, illuminate escape routes to meiotic checkpoints, and give clues for genetic engineering of germ line-permissive chromosomal vectors.

View Article: PubMed Central - PubMed

Affiliation: Human Genome Laboratory, Department of Human Genetics, Flanders Interuniversity Institute for Biotechnology, University of Leuven, Belgium.

ABSTRACT
We analyzed transmission of a ring minichromosome (MC) through mouse spermatogenesis as a monosome and in the presence of a homologue. Mice, either monosomic or disomic for the MC, produced MC+ offspring. In the monosomic condition, most univalents underwent self-synapsis as indicated by STAG3, SCP3, and SCP1 deposition. Fluorescent in situ hybridization and three-dimensional fluorescence microscopy revealed that ring MCs did not participate in meiotic telomere clustering while MC homologues paired at the XY-body periphery. Self-synapsis of MC(s) and association with the XY-body likely allowed them to pass putative pachytene checkpoints. At metaphase I and II, MC kinetochores assembled MAD2 and BUBR1 spindle checkpoint proteins. Unaligned MCs triggered the spindle checkpoint leading to apoptosis of metaphase cells. Other MCs frequently associated with mouse pericentric heterochromatin, which may have allowed them to pass the spindle checkpoint. Our findings indicate a telomere-independent mechanism for pairing of mammalian MCs, illuminate escape routes to meiotic checkpoints, and give clues for genetic engineering of germ line-permissive chromosomal vectors.

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Heterochromatin associations of MCs in MI. (A) Mouse major satellite DNA FISH (green) and α-satellite DNA MC-FISH (red) on an MI spread shows the MC signal touching the pericentric heterochromatin of a mouse bivalent (arrowhead). (B) Frequencies of MC associations with mouse pericentromeric heterochromatin during the first meiotic metaphase. All mice used, except mouse 2MC+-35, are monosomic MC+ mice. In the MI spermatocytes of mouse 2MC+-35, a total of 25 MCs was scored (nine nuclei with one MC; eight nuclei with two MCs). 8% of these MCs were located together and were also associated with pericentric heterochromatin (number implemented in both bars). Another 8% of the MCs localized next to each other and to the euchromatic part of a mouse chromosome (number implemented in both bars).
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fig9: Heterochromatin associations of MCs in MI. (A) Mouse major satellite DNA FISH (green) and α-satellite DNA MC-FISH (red) on an MI spread shows the MC signal touching the pericentric heterochromatin of a mouse bivalent (arrowhead). (B) Frequencies of MC associations with mouse pericentromeric heterochromatin during the first meiotic metaphase. All mice used, except mouse 2MC+-35, are monosomic MC+ mice. In the MI spermatocytes of mouse 2MC+-35, a total of 25 MCs was scored (nine nuclei with one MC; eight nuclei with two MCs). 8% of these MCs were located together and were also associated with pericentric heterochromatin (number implemented in both bars). Another 8% of the MCs localized next to each other and to the euchromatic part of a mouse chromosome (number implemented in both bars).

Mentions: However, the question remained how the majority of mono- and disomic MCs bypass the meiotic spindle checkpoint and are transmitted to the offspring. Univalent human mini- or microchromosomes have been reported to pass through the germ line and show an inherent tendency for centromeric associations (Felbor et al., 2002). Because heterochromatin associations have the capacity to perpetuate the segregation of nonexchange chromosomes in some organisms (for review see McKim and Hawley, 1995; Bernard and Allshire, 2002), we determined whether our MC(s) undergo associations with mouse pericentromeric heterochromatin by MC-specific α-satellite and mouse major satellite DNA FISH to MIs. About 60% of the MCs of monosomic mice showed associations between the MC and the pericentric heterochromatin of MI bivalents (Fig. 9 A). A high frequency of MC–heterochromatin association was also seen in disomic MC spermatocytes (Fig. 9 B). Thus, it may be assumed that centromeric associations, possibly instigated by the general stickiness of pericentric heterochromatin earlier during mouse prophase I (Hsu et al., 1971; Scherthan et al., 1996), may contribute to transmission of MCs through the mammalian germ line.


Telomere-independent homologue pairing and checkpoint escape of accessory ring chromosomes in male mouse meiosis.

Voet T, Liebe B, Labaere C, Marynen P, Scherthan H - J. Cell Biol. (2003)

Heterochromatin associations of MCs in MI. (A) Mouse major satellite DNA FISH (green) and α-satellite DNA MC-FISH (red) on an MI spread shows the MC signal touching the pericentric heterochromatin of a mouse bivalent (arrowhead). (B) Frequencies of MC associations with mouse pericentromeric heterochromatin during the first meiotic metaphase. All mice used, except mouse 2MC+-35, are monosomic MC+ mice. In the MI spermatocytes of mouse 2MC+-35, a total of 25 MCs was scored (nine nuclei with one MC; eight nuclei with two MCs). 8% of these MCs were located together and were also associated with pericentric heterochromatin (number implemented in both bars). Another 8% of the MCs localized next to each other and to the euchromatic part of a mouse chromosome (number implemented in both bars).
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Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2172825&req=5

fig9: Heterochromatin associations of MCs in MI. (A) Mouse major satellite DNA FISH (green) and α-satellite DNA MC-FISH (red) on an MI spread shows the MC signal touching the pericentric heterochromatin of a mouse bivalent (arrowhead). (B) Frequencies of MC associations with mouse pericentromeric heterochromatin during the first meiotic metaphase. All mice used, except mouse 2MC+-35, are monosomic MC+ mice. In the MI spermatocytes of mouse 2MC+-35, a total of 25 MCs was scored (nine nuclei with one MC; eight nuclei with two MCs). 8% of these MCs were located together and were also associated with pericentric heterochromatin (number implemented in both bars). Another 8% of the MCs localized next to each other and to the euchromatic part of a mouse chromosome (number implemented in both bars).
Mentions: However, the question remained how the majority of mono- and disomic MCs bypass the meiotic spindle checkpoint and are transmitted to the offspring. Univalent human mini- or microchromosomes have been reported to pass through the germ line and show an inherent tendency for centromeric associations (Felbor et al., 2002). Because heterochromatin associations have the capacity to perpetuate the segregation of nonexchange chromosomes in some organisms (for review see McKim and Hawley, 1995; Bernard and Allshire, 2002), we determined whether our MC(s) undergo associations with mouse pericentromeric heterochromatin by MC-specific α-satellite and mouse major satellite DNA FISH to MIs. About 60% of the MCs of monosomic mice showed associations between the MC and the pericentric heterochromatin of MI bivalents (Fig. 9 A). A high frequency of MC–heterochromatin association was also seen in disomic MC spermatocytes (Fig. 9 B). Thus, it may be assumed that centromeric associations, possibly instigated by the general stickiness of pericentric heterochromatin earlier during mouse prophase I (Hsu et al., 1971; Scherthan et al., 1996), may contribute to transmission of MCs through the mammalian germ line.

Bottom Line: Fluorescent in situ hybridization and three-dimensional fluorescence microscopy revealed that ring MCs did not participate in meiotic telomere clustering while MC homologues paired at the XY-body periphery.Unaligned MCs triggered the spindle checkpoint leading to apoptosis of metaphase cells.Our findings indicate a telomere-independent mechanism for pairing of mammalian MCs, illuminate escape routes to meiotic checkpoints, and give clues for genetic engineering of germ line-permissive chromosomal vectors.

View Article: PubMed Central - PubMed

Affiliation: Human Genome Laboratory, Department of Human Genetics, Flanders Interuniversity Institute for Biotechnology, University of Leuven, Belgium.

ABSTRACT
We analyzed transmission of a ring minichromosome (MC) through mouse spermatogenesis as a monosome and in the presence of a homologue. Mice, either monosomic or disomic for the MC, produced MC+ offspring. In the monosomic condition, most univalents underwent self-synapsis as indicated by STAG3, SCP3, and SCP1 deposition. Fluorescent in situ hybridization and three-dimensional fluorescence microscopy revealed that ring MCs did not participate in meiotic telomere clustering while MC homologues paired at the XY-body periphery. Self-synapsis of MC(s) and association with the XY-body likely allowed them to pass putative pachytene checkpoints. At metaphase I and II, MC kinetochores assembled MAD2 and BUBR1 spindle checkpoint proteins. Unaligned MCs triggered the spindle checkpoint leading to apoptosis of metaphase cells. Other MCs frequently associated with mouse pericentric heterochromatin, which may have allowed them to pass the spindle checkpoint. Our findings indicate a telomere-independent mechanism for pairing of mammalian MCs, illuminate escape routes to meiotic checkpoints, and give clues for genetic engineering of germ line-permissive chromosomal vectors.

Show MeSH
Related in: MedlinePlus