Telomere stability and development of ctc1 mutants are rescued by inhibition of EJ recombination pathways in a telomerase-dependent manner.
Bottom Line: In this work, we set out to specifically test this hypothesis in the plant, Arabidopsis.It is thus the chromosomal fusions, per se, which are the underlying cause of the severe developmental defects.This rescue is mediated by telomerase-dependent telomere extension, revealing a competition between telomerase and end-joining recombination proteins for access to deprotected telomeres.
Affiliation: Génétique, Reproduction et Développement, UMR CNRS 6293, Clermont Université, INSERM U1103, Aubière, France firstname.lastname@example.org.Show MeSH
Related in: MedlinePlus
Mentions: Unprotected telomeres generated in the absence of the CST complex activate a DNA damage response, as visualized by the detection of Telomere Induced Foci (TIF), phosphorylated H2AX (γ-H2AX) foci that colocalize with telomeres (30). Given the absence of chromosomal fusions and normal growth of ctc1 plants lacking the three EJ pathways, it is clearly of interest to determine whether or not the DDR is activated in these plants. We thus monitored the presence of γ-H2AX foci in nuclei of ctc1 ku80 xrcc1 xpf mutants. As shown in Figure 3A and B, γ-H2AX foci were visible in the nuclei of ctc1 cells lacking the EJ pathway proteins, although in a slightly lower number of nuclei than the ctc1 mutant plants (mean number of foci/nucleus of 0.73 versus 1.04 in ctc1 single mutant). FISH was performed on the same slides using nine subtelomeric specific BACs corresponding to nine of the 10 Arabidopsis chromosome ends. As previously reported for the ctc1 single mutant (30), 68.1% of the γ-H2AX foci colocalize with the subtelomere-specific probes revealing that ctc1 ku80 xrcc1 xpf telomeres are recognized as DNA damage in the mutant plants. Colocalization of γ-H2AX foci with telomeres using a probe against the telomeric repeats (TTTAGGG) however showed that only 17.2% of γ-H2AX foci colocalize with the telomeric repeat sequences. The remaining (50.9%) of TIFs defined by the subtelomeric BAC probes are thus not associated with sequences detectable by the telomeric repeat probe. The DDR is thus being induced at only a subset of dysfunctional telomeres in these plants—mostly those with telomeric sequences too short to be detected by the repeat probe. Our observations suggest that only chromosomes ends with short telomeric repeats activate a DNA damage response.
Affiliation: Génétique, Reproduction et Développement, UMR CNRS 6293, Clermont Université, INSERM U1103, Aubière, France email@example.com.