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. 2010 Sep;16(9):685-94.
doi: 10.1093/molehr/gaq048. Epub 2010 Jun 23.

Telomere lengths in human oocytes, cleavage stage embryos and blastocysts

S Turner  1 , H P Wong, J Rai, G M Hartshorne
Affiliations

Telomere lengths in human oocytes, cleavage stage embryos and blastocysts

S Turner et al. Mol Hum Reprod. 2010 Sep.

Abstract

Telomeres are repeated sequences that protect the ends of chromosomes and harbour DNA repair proteins. Telomeres shorten during each cell division in the absence of telomerase. When telomere length becomes critically short, cell senescence occurs. Telomere length therefore reflects both cellular ageing and capacity for division. We have measured telomere length in human germinal vesicle (GV) oocytes and preimplantation embryos, by quantitative fluorescence in situ hybridization (Q-FISH), providing baseline data towards our hypothesis that telomere length is a marker of embryo quality. The numbers of fluorescent foci suggest that extensive clustering of telomeres occurs in mature GV stage oocytes, and in preimplantation embryos. When calculating average telomere length by assuming that each signal presents one telomere, the calculated telomere length decreased from the oocyte to the cleavage stages, and increased between the cleavage stages and the blastocyst (11.12 versus 8.43 versus 12.22 kb, respectively, P < 0.001). Other methods of calculation, based upon expected maximum and minimum numbers of telomeres, confirm that telomere length in blastocysts is significantly longer than cleavage stages. Individual blastomeres within an embryo showed substantial variation in calculated average telomere length. This study implies that telomere length changes according to the stage of preimplantation embryo development.

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Figures

Figure 1
Figure 1
Telomeres in human embryos. Telomeres were stained using a FITC-labelled pan-telomeric probe (green). All nuclei were counterstained with DAPI (blue). (A) 6-cell embryo resulting in five nuclei with two polar bodies, E and E′ (scale bar = 44 µm). Two of the nuclei (C and D, scale bar = 8.5 µm) are also shown under higher magnification (scale bar = 4 µm). (B) The telomeres in a fixed blastocyst (scale bar = 55 µm).
Figure 2
Figure 2
Numbers of telomere signals identified in GV oocytes and embryonic nuclei at different stages of development (2 cell–7-cell, morula, blastocyst). Box plots represent the median and inter-quartile range, with whiskers representing the 5th and 95th percentiles.
Figure 3
Figure 3
Total telomere-associated fluorescence per nucleus in relation to nuclear area. There was no significant relationship between fluorescence and nuclear area.
Figure 4
Figure 4
Calculated telomere lengths and total fluorescence per nucleus in relation to the number of signals per nucleus. (A) Not significant, (B) P < 0.01.
Figure 5
Figure 5
Calculated telomere lengths of human oocyte GV and embryonic nuclei at different stages of preimplantation development, presented per embryo. Cleavage stage embryos have significantly shorter calculated telomere lengths than GV or blastocyst nuclei (P < 0.001).
Figure 6
Figure 6
Telomere lengths calculated per nucleus for human oocytes and embryos at different stages of preimplantation development, using three different methods of calculation. (A) Telomere length calculated from total fluorescence of the nucleus, divided by the number of telomere signals observed in it. (B) Telomere length calculated in GV oocytes by division of the nuclear fluorescence by 184 and in blastomeres by division by 92. 184 is the number of telomeres known to be present in a normal GV nucleus. Ninety-two is the minimum number of telomeres expected in a normal blastomere nucleus. (C) Telomere length in GV oocytes, calculated as in (B), and in blastomeres by division by 184. About 184 is the maximum number of telomeres expected in a normal blastomere nucleus. (B) and (C) therefore present the upper and lower telomere length estimates of blastomeres according to predicted numbers of telomeres. (A) and (C), Telomere length shorter in cleavage stage blastomeres than blastocyst or GV nuclei. P < 0.001. (B) Telomere length longer (P < 0.001) in blastocyst nuclei than cleavage stage or GV nuclei. No significant difference between GV nuclei and cleavage stage blastomeres.
Figure 7
Figure 7
Average calculated telomere lengths of individual human embryos originating from different patients. The embryos are arranged into eight groups according to the couple from whom they originated. Couple 8 donated the morula, although the other embryos are from 2-cell to 8-cell stage.
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