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Genes encoding ribosomal RNA (rDNA) are essential for cell survival and are particularly sensitive to factors leading to genomic instability. Their repetitive character makes them prone to inappropriate recombinational events arising from collision of transcriptional and replication machineries, resulting in unstable rDNA copy numbers. In this review, we summarize current knowledge on the structure and organization of rDNA, its role in sensing changes in the genome, and its linkage to aging. We also review recent findings on the main factors involved in chromatin assembly and DNA repair in the maintenance of rDNA stability in the model plants Arabidopsis thaliana and the moss Physcomitrella patens, providing a view across the plant evolutionary tree.

Abstract Replication protein A (RPA) is essential for many facets of DNA metabolism. The RPA gene family expanded in Arabidopsis thaliana with five phylogenetically distinct RPA1 subunits (RPA1A-E), two RPA2 (RPA2A and B), and two RPA3 (RPA3A and B). RPA1 paralogs exhibit partial redundancy and functional specialization in DNA replication (RPA1B and RPA1D), repair (RPA1C and RPA1E), and meiotic recombination (RPA1A and RPA1C). Here, we show that RPA subunits also differentially impact telomere length set point. Loss of RPA1 resets bulk telomeres at a shorter length, with a functional hierarchy for replication group over repair and meiosis group RPA1 subunits. Plants lacking RPA2A, but not RPA2B, harbor short telomeres similar to the replication group. Telomere shortening does not correlate with decreased telomerase activity or deprotection of chromosome ends in rpa mutants. However, in vitro assays show that RPA1B2A3B unfolds telomeric G-quadruplexes known to inhibit replications fork progression. We also found that ATR deficiency can partially rescue short telomeres in rpa2a mutants, although plants exhibit defects in growth and development. Unexpectedly, the telomere shortening phenotype of rpa2a mutants is completely abolished in plants lacking the RTEL1 helicase. RTEL1 has been implicated in a variety of nucleic acid transactions, including suppression of homologous recombination. Thus, the lack of telomere shortening in rpa2a mutants upon RTEL1 deletion suggests that telomere replication defects incurred by loss of RPA may be bypassed by homologous recombination. Taken together, these findings provide new insight into how RPA cooperates with replication and recombination machinery to sustain telomeric DNA.

Background Neuroblastoma, a neuroendocrine tumor originating from the sympathetic ganglia, is one of the most common malignancies in childhood. RTEL1 is critical in many fundamental cellular processes, such as DNA replication, DNA damage repair, genomic integrity, and telomere stability. Single nucleotide polymorphisms (SNPs) in the RTEL1 gene have been reported to confer susceptibility to multiple cancers, but their contributing roles in neuroblastoma remain unclear. Methods We conducted a study on 402 neuroblastoma cases and 473 controls to assess the association between four RTEL1 SNPs (rs3761124 T>C, rs3848672 T>C, rs3208008 A>C and rs2297441 G>A) and neuroblastoma susceptibility. Results Our results show that rs3848672 T>C is significantly associated with an increased risk of neuroblastoma [CC vs. TT/TC: adjusted odds ratio (OR)=1.39, 95% confidence interval (CI)=1.02-1.90, P =0.038]. The stratified analysis further indicated that boy carriers of the rs3848672 CC genotype had a higher risk of neuroblastoma, and all carriers had an increased risk of developing neuroblastoma of mediastinum origin. Moreover, the rs2297441 AA genotype increased neuroblastoma risk in girls and predisposed children to neuroblastoma arising from retroperitoneal. Conclusion Our study indicated that the rs3848672 CC and rs2297441 AA genotypes of the RTEL1 gene are significantly associated with an increased risk of neuroblastoma in Chinese children in a gender- and site-specific manner.

Gliomas are the most common primary intracranial tumor worldwide. The maintenance of telomeres serves as an important biomarker of some subtypes of glioma. In order to investigate the biological role of RTEL1 in glioma. Relative telomere length (RTL) and RTEL1 mRNA was explored and regression analysis was performed to further examine the relationship of the RTL and the expression of RTEL1 with clinicopathological characteristics of glioma patients. We observed that high expression of RTEL1 is positively correlated with telomere length in glioma tissue, and serve as a poor prognostic factor in TERT wild-type patients. Further in vitro studies demonstrate that RTEL1 promoted proliferation, formation, migration and invasion ability of glioma cells. In addition, in vivo studies also revealed the oncogene role of RTEL1 in glioma. Further study using RNA sequence and phospho-specific antibody microarray assays identified JNK/ELK1 signaling was up-regulated by RTEL1 in glioma cells through ROS. In conclusion, our results suggested that RTEL1 promotes glioma tumorigenesis through JNK/ELK1 cascade and indicate that RTEL1 may be a prognostic biomarker in gliomas.

Background Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is a novel coronavirus that caused an ongoing pandemic of a pathology termed Coronavirus Disease 19 (COVID-19). Several studies reported that both COVID-19 and RTEL1 variants are associated with shorter telomere length, but a direct association between the two is not generally acknowledged. Here we demonstrate that up to 8.6% of severe COVID-19 patients bear RTEL1 ultra-rare variants, and show how this subgroup can be recognized. Methods A cohort of 2246 SARS-CoV-2-positive subjects, collected within the GEN-COVID Multicenter study, was used in this work. Whole exome sequencing analysis was performed using the NovaSeq6000 System, and machine learning methods were used for candidate gene selection of severity. A nested study, comparing severely affected patients bearing or not variants in the selected gene, was used for the characterisation of specific clinical features connected to variants in both acute and post-acute phases. Results Our GEN-COVID cohort revealed a total of 151 patients carrying at least one RTEL1 ultra-rare variant, which was selected as a specific acute severity feature. From a clinical point of view, these patients showed higher liver function indices, as well as increased CRP and inflammatory markers, such as IL-6. Moreover, compared to control subjects, they present autoimmune disorders more frequently. Finally, their decreased diffusion lung capacity for carbon monoxide after six months of COVID-19 suggests that RTEL1 variants can contribute to the development of SARS-CoV-2-elicited lung fibrosis. Conclusion RTEL1 ultra-rare variants can be considered as a predictive marker of COVID-19 severity, as well as a marker of pathological evolution in pulmonary fibrosis in the post-COVID phase. This notion can be used for a rapid screening in hospitalized infected people, for vaccine prioritization, and appropriate follow-up assessment for subjects at risk. Trial Registration NCT04549831 ( www.clinicaltrial.org )

Gastric cancer (GC) is one of the most common cancers worldwide, with increasing incidence and mortality rates. It is typically diagnosed at advanced stages, leading to a poor prognosis. GC is a highly heterogeneous disease and its progression is associated with complex interplay between genetic and environmental factors. Identifying novel genes and pathways involved in GC development is crucial for improving the therapeutic outcome. Regulator of Telomerase Length 1 (RTEL1) has been found to maintain telomere stability through its helicase activity, facilitating telomere reconstruction and repair. However, the precise role of RTEL1 in human cancers, particularly in GC, is not yet fully understood. In this study, we observed significantly increased RTEL1 expression in GC tissues, which was associated with a poor prognosis. Functionally, RTEL1 promotes GC cell proliferation both in vitro and in vivo. Additionally, RTEL1 appears to regulate multiple signaling pathways, with a particular promoting effect on the cell cycle progression. Notably, CDC23 and TRIP13 are potential downstream target genes of RTEL1, which may mediate its tumor-promoting effects in GC. These findings suggest that RTEL1 plays a critical role in GC tumorigenesis and could be a promising target for the therapy and prognosis of GC.

Background The telomere biology disorders (TBDs) include a range of multisystem diseases characterized by mucocutaneous symptoms and bone marrow failure. In dyskeratosis congenita (DKC), the clinical features of TBDs stem from the depletion of crucial stem cell populations in highly proliferative tissues, resulting from abnormal telomerase function. Due to the wide spectrum of clinical presentations and lack of a conclusive laboratory test it may be challenging to reach a clinical diagnosis, especially if patients lack the pathognomonic clinical features of TBDs. Methods Clinical sequencing was performed on a cohort of patients presenting with variable immune phenotypes lacking molecular diagnoses. Hypothesis-free whole-exome sequencing (WES) was selected in the absence of compelling diagnostic hints in patients with variable immunological and haematological conditions. Results In four patients belonging to three families, we have detected five novel variants in known TBD-causing genes ( DKC1 , TERT and RTEL1 ). In addition to the molecular findings, they all presented shortened blood cell telomeres. These findings are consistent with the displayed TBD phenotypes, addressing towards the molecular diagnosis and subsequent clinical follow-up of the patients. Conclusions Our results strongly support the utility of WES-based approaches for routine genetic diagnostics of TBD patients with heterogeneous or atypical clinical presentation who otherwise might remain undiagnosed.

[This corrects the article on p. 449 in vol. 8, PMID: 28507545.].

In sporadic idiopathic pulmonary fibrosis (sIPF) and pulmonary fibrosis caused by a mutation in telomere (TRG-PF) or surfactant related genes (SRG-PF), there are a number of aberrant cellular processes known that can lead to fibrogenesis. We investigated whether RNA expression of genes involved in these processes differed between sIPF, TRG-PF, and SRG-PF and whether expression levels were associated with survival. RNA expression of 28 genes was measured in lung biopsies of 26 sIPF, 17 TRG-PF, and 6 SRG-PF patients. Significant differences in RNA expression of TGFBR2 (p = 0.02) and SFTPA2 (p = 0.02) were found between sIPF, TRG-PF, and SRG-PF. Patients with low (

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