Telomere length dynamics in response to DNA damage in malaria parasites

Abstract

Malaria remains a major cause of morbidity and mortality in the developing world. Recent work has implicated chromosome end stability and the repair of DNA breaks through telomere healing as potent drivers of variant antigen diversification, thus associating basic mechanisms for maintaining genome integrity with aspects of host-parasite interactions. Here we applied long-read sequencing technology to precisely examine the dynamics of telomere addition and chromosome end stabilization in response to double-strand breaks within subtelomeric regions. We observed that the process of telomere healing induces the initial synthesis of telomere repeats well in excess of the minimal number required for end stability. However, once stabilized, these newly created telomeres appear to function normally, eventually returning to a length nearing that of intact chromosome ends. These results parallel recent observations in humans, suggesting an evolutionarily conserved mechanism for chromosome end repair.

Keywords: astrobiology; chromosome organization; omics; parasitology.

Graphical abstract

Figure 1

Total telomere length distributions in irradiated and wild-type parasites (A) Number of telomere reads assigned to each chromosome end by radiation status, irradiated (red) or wild-type (blue). (B) Comparison of telomere length distributions of the irradiated (red) and wild-type (blue) samples. The red and blue dashed lines indicate the modes of the irradiated and wild-type samples, respectively. ∗ Designates a duplication of the 5′ end of chromosome 9 onto the 3′ ends of chromosomes 12 and 13 (Calhoun et al., 2017).

Figure 2

Comparison of telomere lengths by end and radiation status Red boxes indicate telomere healing events resulting from exposure to radiation, whereas green boxes indicate telomere healing events found in the original population, before exposure to radiation.

Figure 3

Telomere lengths by radiation and healing status Telomere lengths were assessed after a random downsampling to n = 35. Welch's t test was used to determine significance. The samples are ordered from left to right as irradiated healed telomere tracts (irr-H), irradiated past healed telomere tracts (irr-PH), irradiated non-healed telomere tracts (irr-NH), wild-type past healed telomere tracts (wt-PH), and wild-type non-healed telomere tracts (wt-NH). p value annotation legend: ns: 5.00x10^-2 < p ≤ 1.00x10; ∗∗1.00x10^-3 < p ≤ 1.00x10^-2; ∗∗∗∗p ≤ 1.00x10^-4.

Figure 4

Sample size impact on p value Sample size was randomly downsampled from the minimum number of reads per grouping (1,075 reads in the irradiated healed set). p Values were generated based on different grouping comparisons while sample size was progressively increased from n = 35. The p values generated approached zero in an exponential fashion, therefore -log(p) was plotted to make differences discernable. Irradiated healed telomeres versus wild-type non-healed (irr-H_wt-NH) (red) and irradiated non-healed telomeres versus wild-type non-healed telomeres (irr-NH_wt-NH) (blue) comparisons consistently displayed the most significant differences in telomere length. Wild-type past healed telomeres versus wild-type non-healed telomeres (wt-PH_wt-NH) (green) and irradiated healed telomeres versus irradiated non-healed telomeres (irr-H_irr-NH) (purple) displayed marginally significant telomere length differences, and the length difference between irradiated past healed telomeres and irradiated non-healed telomeres (irr-PH_irr-NH) (orange) was non-significant initially but became more significant as the sample size increased.