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. 1997 Jul 8;94(14):7423-8.
doi: 10.1073/pnas.94.14.7423.

Telomeres in the mouse have large inter-chromosomal variations in the number of T2AG3 repeats

J M Zijlmans  1 , U M Martens, S S Poon, A K Raap, H J Tanke, R K Ward, P M Lansdorp
Affiliations

Telomeres in the mouse have large inter-chromosomal variations in the number of T2AG3 repeats

J M Zijlmans et al. Proc Natl Acad Sci U S A. .

Abstract

The ultra-long telomeres that have been observed in mice are not in accordance with the concept that critical telomere shortening is related to aging and immortalization. Here, we have used quantitative fluorescence in situ hybridization to estimate (T2AG3)n lengths of individual telomeres in various mouse strains. Telomere lengths were very heterogeneous, but specific chromosomes of bone marrow cells and skin fibroblasts from individual mice had similar telomere lengths. We estimate that the shortest telomeres are around 10 kb in length, indicating that each mouse cell has a few telomeres with (T2AG3)n lengths within the range of human telomeres. These short telomeres may be critical in limiting the replicative potential of murine cells.

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Figures

Figure 1
Figure 1
Quantitative FISH analysis of individual telomeres illustrated on a bone marrow-derived metaphase spread from a BALB/c mouse. (A) Digital image of DAPI-stained chromosomes. (B) Individual telomeres in the Cy-3 fluorescence image. (C) Output of dedicated image analysis software which combines the DAPI and Cy-3 images, identifies chromosomes and telomeres, assigns colors to the four telomeres (purple, red, light and dark blue), calculates the integrated fluorescence intensity for each telomere after correction for background and expresses the integrated fluorescence intensity of individual telomeres of each chromosome in a table. (D) Combination of DAPI and Cy-3 images after assigning pseudocolors—i.e., blue for DAPI and orange for Cy-3, with the use of Adobe photoshop (Adobe Systems, Mountain View, CA). (E) Individual chromosomes after karyotyping according to standard DAPI banding patterns (19). (F) Finally, the integrated fluorescence intensity is expressed for both p- and q-arm telomeres from each karyotyped chromosome.
Figure 2
Figure 2
Telomere fluorescence intensities in three mice, from BALB/c, C3H, and DBA/2 strains respectively. Histograms express the fluorescence intensity and frequency of all individual telomeres from 12 to 15 bone marrow-derived metaphases (A–C). Individual telomeres on the distal q-arm (D–F), and proximal p-arm (G–I) are expressed separately. The differences in median fluorescence intensity between p- and q-arm telomeres were highly significant (P < 0.0001, Wilcoxon rank sum test) in all three mice. Dot plots (J–L) express the fluorescence intensity values of the two sister chromatids (S1 and S2) on each chromosome end. Correlation coefficients (r) varied from 0.88 to 0.90. Telomere fluorescence intensity is expressed so that 1 telomere fluorescence unit (T.F.U.) corresponds to 1 kb of (T2AG3)n sequence according to results from similarly hybridized and analyzed plasmids with a defined (T2AG3)n length.
Figure 3
Figure 3
Short telomeres are present on specific chromosomes and variability in telomere length on homologous chromosomes. Histograms express the fluorescence intensity of individual telomeres from 15 bone marrow- (A) or skin fibroblast-derived (B) metaphases of a single BALB/c mouse. The telomeres on chromosome 2-p (C and D) and 11-p (E and F) are separated in two subpopulations: one derived from homolog with short telomeres (filled bars) and one from the corresponding homolog with longer telomeres (open bars) in each cell. (Lower) Telomeres from chromosome 19-q (G) and 19-p (H) are shown for the bone marrow-derived cells. The 19-q telomeres show a histogram with bimodal distribution originating from one homolog with a longer telomere (I) and one with a shorter telomere (K) in each cell. When the two homologs of chromosome 19 are distinguished according to this difference in 19-q telomeres, there is also a highly significant, reversed difference for p-arm telomeres (J and L). One telomere fluorescence unit (T.F.U.) corresponds to 1 kb of (T2AG3)n length (see also the legend to Fig. 2).
Figure 4
Figure 4
Heterogeneity of Y-chromosome telomeres in four male BALB/c littermates (m1–m4). The open box plots represent all telomeres from 15 bone marrow cells or skin fibroblasts. The hatched box plots represent only the telomeres of the proximal p-arm of the Y-chromosome in the same cell populations. The median telomere fluorescence values for total telomeres varied from 28.4 to 32.0 in the bone marrow and fibroblast populations from the various mice. The median telomere values of Y-p telomeres in each mouse in bone marrow and skin fibroblast, respectively, are as follows: m1, 10.1 and 10.6; m2, 25.0 and 24.0; m3, 20.7 and 22.4; m4, 21.0 and 21.2. One telomere fluorescence unit (T.F.U.) corresponds to 1 kb of (T2AG3)n length (see also the legend to Fig. 2).
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