Jaiswal Rishi K, Garibo Domingo Teresa, Grunchec Héloïse, Singh Komudi, Pirooznia Mehdi, Elhaik Eran, Cohn Marita
Department of Biology, Lund University, Sölvegatan 35, SE-223 62, Lund, Sweden.
Bioinformatics and Computational Core Facility, NIH, Bethesda, MD, USA.
Curr Genet. 2025 Sep 3;71(1):19. doi: 10.1007/s00294-025-01325-w.
Telomerase plays an important role in sustaining eukaryotic linear chromosomes, as elongation of telomeres is needed to counterbalance the shortening occurring in each replication round. Nevertheless, in telomerase-deficient cells, Alternative Lengthening of Telomeres (ALT) pathways can maintain telomeres by employing recombination-based mechanisms. In the budding yeast Naumovozyma castellii, effective activation of the ALT pathway leads to bypass of senescence and supports long-term growth. We found that telomere structures in N. castellii ALT cells are stably maintained at a shortened uniform length over extensive numbers of generations. This is correlated to the spreading of a subtelomeric sequence, TelKO element, to all telomeres. Genome sequencing of the wild-type strain revealed variants of the TelKO element, differing in their lengths, and separate ALT strains are maintained by spreading of distinct TelKO element variants. Although short uniform telomere structures are predominant, sporadic telomere lengthening events occur by addition of long repeated arrays of TelKO elements. The telomere-binding protein Rap1 can bind to TelKO sequences in vitro, indicating a functional role of TelKO elements in providing stability to shortened ALT telomeres. Our results suggest that stable maintenance and telomere functionality may be achieved by incorporating the distal subtelomeric TelKO sequences into the telomeric chromatin cap.
端粒酶在维持真核生物线性染色体方面发挥着重要作用，因为需要延长端粒来抵消每个复制轮次中发生的缩短。然而，在缺乏端粒酶的细胞中，端粒的替代延长（ALT）途径可以通过基于重组的机制来维持端粒。在出芽酵母卡斯泰利瑙莫伏酵母中，ALT途径的有效激活导致衰老的绕过并支持长期生长。我们发现，卡斯泰利瑙莫伏酵母ALT细胞中的端粒结构在大量代中以缩短的均匀长度稳定维持。这与一个亚端粒序列TelKO元件向所有端粒的扩散相关。野生型菌株的基因组测序揭示了TelKO元件的变体，其长度不同，并且不同的ALT菌株通过不同的TelKO元件变体的扩散得以维持。虽然短的均匀端粒结构占主导，但通过添加长的重复TelKO元件阵列会发生零星的端粒延长事件。端粒结合蛋白Rap1在体外可以结合TelKO序列，这表明TelKO元件在为缩短的ALT端粒提供稳定性方面具有功能作用。我们的结果表明，通过将远端亚端粒TelKO序列纳入端粒染色质帽，可以实现稳定维持和端粒功能。
