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Telomere length dynamics and chromosomal instability in cells derived from telomerase mice.

Hande MP, Samper E, Lansdorp P, Blasco MA - J. Cell Biol. (1999)

Bottom Line: Interestingly, the most frequent fusions found in mTER-/- cells were homologous fusions involving chromosome 2.At various points during the growth of the immortal mTER-/- cells, telomere length was stabilized in a chromosome-specific man-ner.This telomere-maintenance in the absence of telomerase could provide the basis for the ability of mTER-/- cells to grow indefinitely and form tumors.

View Article: PubMed Central - PubMed

Affiliation: Terry Fox Laboratory, British Columbia Cancer Research Center, Vancouver, British Columbia V5Z 1L3, Canada.

ABSTRACT
To study the effect of continued telomere shortening on chromosome stability, we have analyzed the telomere length of two individual chromosomes (chromosomes 2 and 11) in fibroblasts derived from wild-type mice and from mice lacking the mouse telomerase RNA (mTER) gene using quantitative fluorescence in situ hybridization. Telomere length at both chromosomes decreased with increasing generations of mTER-/- mice. At the 6th mouse generation, this telomere shortening resulted in significantly shorter chromosome 2 telomeres than the average telomere length of all chromosomes. Interestingly, the most frequent fusions found in mTER-/- cells were homologous fusions involving chromosome 2. Immortal cultures derived from the primary mTER-/- cells showed a dramatic accumulation of fusions and translocations, revealing that continued growth in the absence of telomerase is a potent inducer of chromosomal instability. Chromosomes 2 and 11 were frequently involved in these abnormalities suggesting that, in the absence of telomerase, chromosomal instability is determined in part by chromosome-specific telomere length. At various points during the growth of the immortal mTER-/- cells, telomere length was stabilized in a chromosome-specific man-ner. This telomere-maintenance in the absence of telomerase could provide the basis for the ability of mTER-/- cells to grow indefinitely and form tumors.

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Models for the  generation of chromosomal  fusions by telomere loss.  (Top) Replication and segregation of a mouse chromatid  with normal telomeres.  (Middle and bottom) Shortening of p- or q-arm telomeres to a critical length leads  to fusion of sister chromatids  after replication. The subsequent failure in the separation of these fusions might  result in a daughter cell (1)  harboring a Robertsonian-like configuration (middle)  or a dicentric chromosome  (bottom) and a second  daughter cell (2) that has  lost a chromosome. Fused  chromosomes may undergo  successive cycles of breakage-fusion-bridge and are inherently unstable (reviewed  in de Lange, 1995).
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Figure 5: Models for the generation of chromosomal fusions by telomere loss. (Top) Replication and segregation of a mouse chromatid with normal telomeres. (Middle and bottom) Shortening of p- or q-arm telomeres to a critical length leads to fusion of sister chromatids after replication. The subsequent failure in the separation of these fusions might result in a daughter cell (1) harboring a Robertsonian-like configuration (middle) or a dicentric chromosome (bottom) and a second daughter cell (2) that has lost a chromosome. Fused chromosomes may undergo successive cycles of breakage-fusion-bridge and are inherently unstable (reviewed in de Lange, 1995).

Mentions: No fusions were detected in metaphases analyzed from early passage primary wt cells (Table I). In the case of mTER−/− primary cells, the frequency of fusions increased significantly from 0.07 fusions per metaphase in mTER−/− cells from the 1st generation (KO19-G1) to an average of 1.04 fusions (range from 0.5 to 1.72) per metaphase in seven independently derived mTER−/− cells from 6th generation embryos (KO9-G6, KO11-G6, and KO1-G6 to KO5-G6; Table I). Interestingly, cytogenetic analysis of the cells derived from seven independent 6th generation embryos revealed that an average of 41% of the fusions was type II fusions. Chromosome painting showed that 70% of these type II fusions were homologous fusions involving 2p (2p-to-2p fusions; see Fig. 4 for example) and only 2% involved chromosome 11. The dramatic increase in chromosome 2 but not chromosome 11p-arm fusions in 6th generation mTER−/− cells, is probably the consequence of 2p-telomeres shortening from 26.0 ± 2.8 kb in the wt cells, to an average of 7 kb, shorter than the average of all telomeres in cells from the 6th generation. In this regard, in 6th generation cells derived from embryo KO9-G6, 2p-telomeres were only an estimated 0.15 kb long and 100% of type II fusions were 2p-to-2p fusions. The homologous nature of these fusions indicates that they are likely to be the result of a failure to separate sister chromatids during mitosis (see model in Fig. 5). Interestingly, fusions involving chromosome 2 were stably maintained in two different G6 cell lines studied, KO9-G6 and KO11-G6, at least for >80 PDs (Table II, see Discussion). Other fusions found in primary KO9-G6 cells included type I fusions (35%), and less frequently, type III (8%) and type V (18.4%) fusions (see Fig. 4 for examples and Table I for data). Taken together, chromosome 2 seems to be more frequently involved in chromosome fusions than other chromosomes in the mTER−/− MEFs, although we can not rule out that other chromosomes might occasionally be involved in fusions in mTER−/− cells (Lee et al., 1998).


Telomere length dynamics and chromosomal instability in cells derived from telomerase mice.

Hande MP, Samper E, Lansdorp P, Blasco MA - J. Cell Biol. (1999)

Models for the  generation of chromosomal  fusions by telomere loss.  (Top) Replication and segregation of a mouse chromatid  with normal telomeres.  (Middle and bottom) Shortening of p- or q-arm telomeres to a critical length leads  to fusion of sister chromatids  after replication. The subsequent failure in the separation of these fusions might  result in a daughter cell (1)  harboring a Robertsonian-like configuration (middle)  or a dicentric chromosome  (bottom) and a second  daughter cell (2) that has  lost a chromosome. Fused  chromosomes may undergo  successive cycles of breakage-fusion-bridge and are inherently unstable (reviewed  in de Lange, 1995).
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2132934&req=5

Figure 5: Models for the generation of chromosomal fusions by telomere loss. (Top) Replication and segregation of a mouse chromatid with normal telomeres. (Middle and bottom) Shortening of p- or q-arm telomeres to a critical length leads to fusion of sister chromatids after replication. The subsequent failure in the separation of these fusions might result in a daughter cell (1) harboring a Robertsonian-like configuration (middle) or a dicentric chromosome (bottom) and a second daughter cell (2) that has lost a chromosome. Fused chromosomes may undergo successive cycles of breakage-fusion-bridge and are inherently unstable (reviewed in de Lange, 1995).
Mentions: No fusions were detected in metaphases analyzed from early passage primary wt cells (Table I). In the case of mTER−/− primary cells, the frequency of fusions increased significantly from 0.07 fusions per metaphase in mTER−/− cells from the 1st generation (KO19-G1) to an average of 1.04 fusions (range from 0.5 to 1.72) per metaphase in seven independently derived mTER−/− cells from 6th generation embryos (KO9-G6, KO11-G6, and KO1-G6 to KO5-G6; Table I). Interestingly, cytogenetic analysis of the cells derived from seven independent 6th generation embryos revealed that an average of 41% of the fusions was type II fusions. Chromosome painting showed that 70% of these type II fusions were homologous fusions involving 2p (2p-to-2p fusions; see Fig. 4 for example) and only 2% involved chromosome 11. The dramatic increase in chromosome 2 but not chromosome 11p-arm fusions in 6th generation mTER−/− cells, is probably the consequence of 2p-telomeres shortening from 26.0 ± 2.8 kb in the wt cells, to an average of 7 kb, shorter than the average of all telomeres in cells from the 6th generation. In this regard, in 6th generation cells derived from embryo KO9-G6, 2p-telomeres were only an estimated 0.15 kb long and 100% of type II fusions were 2p-to-2p fusions. The homologous nature of these fusions indicates that they are likely to be the result of a failure to separate sister chromatids during mitosis (see model in Fig. 5). Interestingly, fusions involving chromosome 2 were stably maintained in two different G6 cell lines studied, KO9-G6 and KO11-G6, at least for >80 PDs (Table II, see Discussion). Other fusions found in primary KO9-G6 cells included type I fusions (35%), and less frequently, type III (8%) and type V (18.4%) fusions (see Fig. 4 for examples and Table I for data). Taken together, chromosome 2 seems to be more frequently involved in chromosome fusions than other chromosomes in the mTER−/− MEFs, although we can not rule out that other chromosomes might occasionally be involved in fusions in mTER−/− cells (Lee et al., 1998).

Bottom Line: Interestingly, the most frequent fusions found in mTER-/- cells were homologous fusions involving chromosome 2.At various points during the growth of the immortal mTER-/- cells, telomere length was stabilized in a chromosome-specific man-ner.This telomere-maintenance in the absence of telomerase could provide the basis for the ability of mTER-/- cells to grow indefinitely and form tumors.

View Article: PubMed Central - PubMed

Affiliation: Terry Fox Laboratory, British Columbia Cancer Research Center, Vancouver, British Columbia V5Z 1L3, Canada.

ABSTRACT
To study the effect of continued telomere shortening on chromosome stability, we have analyzed the telomere length of two individual chromosomes (chromosomes 2 and 11) in fibroblasts derived from wild-type mice and from mice lacking the mouse telomerase RNA (mTER) gene using quantitative fluorescence in situ hybridization. Telomere length at both chromosomes decreased with increasing generations of mTER-/- mice. At the 6th mouse generation, this telomere shortening resulted in significantly shorter chromosome 2 telomeres than the average telomere length of all chromosomes. Interestingly, the most frequent fusions found in mTER-/- cells were homologous fusions involving chromosome 2. Immortal cultures derived from the primary mTER-/- cells showed a dramatic accumulation of fusions and translocations, revealing that continued growth in the absence of telomerase is a potent inducer of chromosomal instability. Chromosomes 2 and 11 were frequently involved in these abnormalities suggesting that, in the absence of telomerase, chromosomal instability is determined in part by chromosome-specific telomere length. At various points during the growth of the immortal mTER-/- cells, telomere length was stabilized in a chromosome-specific man-ner. This telomere-maintenance in the absence of telomerase could provide the basis for the ability of mTER-/- cells to grow indefinitely and form tumors.

Show MeSH
Related in: MedlinePlus