BackgroundEsophageal cancer (EC) is a common malignancy with poor prognosis. Telomeres, composed of repetitive DNA sequences and shelterin complexes, play important roles in tumor biology. However, the prognostic value of telomere-related genes (TRGs) in EC remains unclear.MethodsTRGs were obtained from TelNet, and transcriptomic and clinical data were collected from The Cancer Genome Atlas (TCGA). Prognostic TRGs were identified using multivariate Cox regression analysis, Least Absolute Shrinkage and Selection Operator (LASSO), Random Forest (RF), and Support Vector Machine (SVM) algorithms to construct a risk model. Model performance was evaluated by Kaplan–Meier(K-M) and Receiver Operating Characteristic (ROC) analyses, and a nomogram integrating clinical variables was developed. Somatic mutations, immune infiltration, immunotherapy response, and drug sensitivity were compared between high- and low-risk groups. In addition, functional assays were performed to verify the biological role of the key gene PTGES3.ResultsSix TRGs significantly associated with prognosis were identified to establish a risk model. High-risk patients had worse survival, higher TP53 and TTN mutation rates, altered immune infiltration, poorer predicted immunotherapy response, and distinct drug sensitivity profiles. Knockdown of PTGES3 significantly suppressed EC cell migration, invasion, and clonogenic ability, supporting its oncogenic role.ConclusionA TRGs-based prognostic model effectively predicts survival in EC and reveals associations with somatic mutations, immune infiltration, and drug sensitivity. Functional validation of PTGES3 further supports its potential as a therapeutic target.Supplementary InformationThe online version contains supplementary material available at 10.1186/s13019-025-03727-w.

TRF1 is a subunit of the shelterin complex that binds to and protects the linear ends of chromosomes known as telomeres. Both genetic deletion and chemical inhibition of TRF1 have been shown to block the growth of lung carcinoma, glioblastoma, and renal cell carcinoma in mice without affecting mouse survival or tissue function, making TRF1 a potential therapeutic target in cancer1–3. Here, we report the discovery of a series of fragment hits that bind at the interface between the TRFH domain of TRF1 (TRF1TRFH) and a peptide of TIN2 (TIN2TBM), an interaction essential for the recruitment of TRF1 to shelterin, using X-ray crystallography (XChem) and ligand-observed NMR (LO-NMR) fragment screening. We discovered a first-in-class inhibitor of the TRF1:TIN2 interaction (compound 40) that binds to TRF1TRFH with a KD of 29 µM (95% CI: 20–41 µM), displaces a TIN2 probe with an IC50 of 67 µM (95% CI: 10–120 µM), and expels TRF1 from purified shelterin. Aided by a novel crystal system of TRF1TRFH, we characterised fragments binding in a hotspot at the TRF1:TIN2 interface; these will serve as a starting point for the structure-guided development of potent inhibitors of TRF1 protein:protein interactions to disrupt shelterin complex assembly.Supplementary InformationThe online version contains supplementary material available at 10.1038/s41598-025-23858-3.

A non-telomeric role of POT1a in regulating HSC metabolism via TIN2 localization

Background: Germline variants in the telomere-regulating genes (TRG) of the shelterin complex have recently been associated with long telomere length and increased risk of several tumors, including thyroid cancer (TC). We aimed to validate these findings in a different ancestral population. Patients and Methods: We conducted a cross-sectional study in a tertiary care hospital in Saudi Arabia. We included 189 patients with sporadic TC and 63 members of 26 families with at least two members with TC. Whole exome sequencing was performed on genomic DNA isolated from peripheral blood, and bioinformatics analysis focused on TRG variants. Results: In the 189 sporadic TC patients, 8 TRG variants were found in 39 patients (20.6%). These included 3 ACD variants in 30 patients (NM_001082486.2: c.22G>A, c.617A>C and c.824C>T), 2 variants in TERF1 in 4 patients (NM_003218.4: c.162_163insGAG and c.1126C>G) and 3 variants in TERT in 5 patients (NM_198253: c.769G>T, c.76A>G and c.1323_1325del). In 63 patients with a family history of TC (26 families), only two variants were found: a TERF1 variant in one patient (NM_017489.3: c.347C>T), and an ACD variant (NM_001082486.2: c.22G>A) in 2 affected members of a 4-member family with papillary TC and in another patient from an unrelated family. All the TRG variants found in this study were either variants of unknown significance or likely benign. The TRG variants described in the recent studies from the United States were absent in the current study and our local database of >18,000 exomes. Conclusions: Unlike the recently reported results from the United States, TRG variants do not seem to play a role in sporadic or familial TC samples from the Saudi Arabian population. These results suggest that the role of TRG variants may vary among different ethnic populations and call for validation of these findings in diverse populations.

TRF1, a component of the telomere shelterin complex, plays crucial roles in telomere protection, telomere length regulation, and stemness. Here, we describe a previously unknown connection between TRF1 and metabolism. Telomere attrition has been linked to obesity. Our study reveals that Trf1-deficient mice exhibit a leaner phenotype, reduced adiposity, and improved glucose tolerance, even when subjected to a high-fat diet, independently of telomere shortening. These findings uncover a previously unknown role of TRF1 in regulating metabolism.

TRF1 and TRF2 form distinct shelterin subcomplexes at telomeres

Abstract Background The telomere is essential for protecting the stability and chromosomal integrity of the human chromosome and has been proposed as a biological biomarker for cancer and ageing-related diseases. Telomeres have received a lot of interest in the last decade because of their possible role in human (in)fertility. Numerous investigations have been carried out in the past to look at the connections between the clinical outcome, male sperm parameters, telomere length (TL), and embryonic development. However, the results appear to be definitive regarding the potential relationship between male (in)fertility, sperm quality, and leukocyte telomere length (LTL) and/or sperm telomere length (STL). Objective The aim of this meta-analysis was to evaluate the clinical significance and sperm cell reliability for TL assessment (sperm/leukocytes) as a novel predictive biomarker in male (in)fertility, with an overview of general trends. Methods A comprehensive systematic search was carried out for relevant research. This evaluation comprised 34 scientific research publications that examined the association between sperm/LTL and sperm quality, male (in)fertility, DNA Fragmentation Index, reactive oxygen species (ROS), embryonic development, Shelterin complex participation, and protamine insufficiency. Results The meta-analysis revealed that altered sperm parameters with high DNA Fragmentation Index, increased level of ROS, protamine insufficiency, and short STL are all positively correlated with male (in)fertility. The receiver operating characteristic (ROC) analysis was performed to evaluate the effectiveness of the STL assay as a diagnostic tool. The optimal cut-off value for STL in determining male (in)fertility is 1.0, which demonstrates a sensitivity and specificity of 73%. However, there is limited consistency in the data regarding the effects of STL on clinical pregnancy rates and embryonic development. Short conclusion As per reported literatures, altered STL is positively correlated with sperm parameters, a high DNA Fragmentation Index, increased level of ROS, protamine insufficiency, and male (in)fertility. This correlation indicates a strong prognostic potential for male (in)fertility issues. With the evolving an advancing scientific knowledge, STL might be adopted as a novel biomarker for detecting sperm quality, male (in)fertility, and forecasting embryonic development in the near future. A larger cohort of infertile populations must be studied for a better correlation, even if this analysis may provide an overview of trends in the relationship between TL and infertility attributes. Trial registration Registered in the PROSPERO international prospective registry of systematic reviews (CRD42024569515).

Topoisomerase IIIα controls alternative lengthening of telomeres

Regulation of shelterin proteins TERF2IP and TRF2 by the MLL2-H3K4me3-p65 axis drives hyperglycemia-dependent endothelial senescence.

Telomere biology still remains a topic of interest in life sciences. Analysis of several thousand clinical samples from healthy individuals performed in recent years has shown that the telomere length (TL) in peripheral blood leukocytes correlates with the TL in cells of internal organ and reflects their condition. TLdecreases under the influence of damaging factors and can serve as an indicator of health status. Thetelomere shortening leads to the cell proliferation arrest and is considered as a marker of replicative aging of proliferating cells. A decrease in the TL in peripheral blood leukocytes is viewed as an indicator of organism aging. Recent studies have allowed to formulate the concept on the role of the CST-polymerase α/primase in the C-strand fill in after completion of 3'G overhang synthesis by telomerase during telomere replication. Thediscovery of the telomeric RNA (TERRA) and its role in the regulation of telomerase activity (TA) and alternative lengthening of telomeres, as well as the possibility of TERRA translation, has provided evidence of the complex epigenetic regulation of the TL maintenance. Analysis of the published data indicates that telomeres are dynamic structures, whose length undergoes significant changes under the influence of damaging factors. TL is determined not only by the chronological age, but also by the exposure to the exogenous and endogenous deleterious factors during the lifetime. A decrease in the TL due to inherited mutations in the genes coding for proteins involved in the telomere structure formation and telomere replication (primarily, proteins of the shelterin and CST complexes and telomerase) has been found in a number of hereditary diseases - telomeropathies. The assessment of TL and TA is of great importance for the diagnostics of telomeropathies and can be useful in the diagnostics of cancer. Analysis of TL can be used for monitoring the health status (e.g., in the case of exposure to ionizing radiation and space flight factors), as well as predicting individual's sensitivity to the action of various damaging agents. The application of modern advancement in genetic technologies in the analysis of TL and TA makes it available for the use in clinical and epidemiological studies, diagnostics of telomeropathies, and monitoring of astronauts' health.

Glioblastoma (GBM) is a kind of intractable brain tumor. The effect of surgical treatment, radiotherapy and chemotherapy is not ideal. TRF1 is one of the important components of shelterin complex, which plays an important role in human telomere protection. Previous studies have reported that inhibition of TRF1 expression can inhibit the growth and proliferation of GBM without causing serious physiological dysfunction. However, the specific mechanism of inhibition of GBM growth and proliferation caused by decreased TRF1 expression has not been fully elucidated. To further elucidate this mechanism, we knockdown TRF1 by siRNA. We detected the levels of cell senescence, autophagy through biological experiments. It has been found that the knockdown of TRF1 can cause significant increase in the aging, autophagy of GBM. In addition, SIRT-6 is a NAD<sup>+</sup>- dependent deacetylase. Previous studies have reported that SIRT-6 can maintain the stability of telomere function. Moreover, telomere dysfunction can cause the decrease of SIRT-6 expression. Therefore, we want to study the effect of SIRT-6 expression level on TRF1 knockdown induced aging, autophagy in GBM. The experimental results showed that the knockdown of TRF1 caused the decrease of SIRT-6 expression level, and the increase of SIRT-6 expression level could inhibit the aging, autophagy caused by TRF1 knockdown. This study provides a new direction for the treatment of GBM.

ABSTRACTReplicative senescence occurs in response to shortened telomeres and is triggered by ATM and TP53‐mediated DNA damage signaling that blocks replication. hTERT lengthens telomeres, which is thought to block damage signaling and the onset of senescence. We find that normal diploid fibroblasts expressing hTERT mutants unable to maintain telomere length do not initiate DNA damage signaling and continue to replicate, despite having telomeres shorter than senescent cells. The TRF1 and TRF2 DNA binding proteins of the shelterin complex stabilize telomeres, and we find that expression of different mutant hTERT proteins decreases levels of the Siah1 E3 ubiquitin ligase that targets TRF2 to the proteasome, by increasing levels of the CDC20 and FBXO5 E3 ligases that target Siah1. This restores the TRF2:TRF1 ratio to block the activation of ATM and subsequent activation of TP53 that is usually associated with DNA damage‐induced senescence signaling. All hTERT variants reduce DNA damage signaling, and this occurs concomitantly with telomeres assuming a more compact, denser conformation than senescent cells as measured by super‐resolution microscopy. This indicates that hTERT variants induce TRF2‐mediated telomere compaction that is independent of telomere length, and it plays a dominant role in regulating the DNA damage signaling that induces senescence and blocks replication of human fibroblasts. These observations support the idea that very short telomeres often seen in cancer cells may fail to induce senescence due to selective stabilization of components of the shelterin complex, increasing telomere density, rather than maintaining telomere length via the reverse transcriptase activity of hTERT.

Abstract Telomerase Reverse Transcriptase (TERT), the catalytic subunit of telomerase, is essential for telomere maintenance, elongating the G-strand of telomeric DNA using its associated RNA template (TR). Recruitment of TERT to telomeres is mediated by the shelterin component TPP1. While TERT is highly expressed in cancer cells, efforts to target its telomeric function have shown limited clinical efficacy. Recent studies have identified noncanonical roles for TERT, particularly in the DNA damage response (DDR), suggesting alternative therapeutic opportunities. Notably, TERT inhibitors sensitize cancer cells to radiotherapy, though the mechanisms underlying this effect remain unclear. To address this gap, we established a mutant TERT phenotyping system to study how TERT variants affect the DDR. Using a tetracycline-inducible shRNA-miR knockdown system in MCF7 and HeLa cells, we targeted endogenous TERT and complemented with transfected wildtype or mutant TERT, validating expression by Western blot. Cells expressing only transfected TERT were irradiated with 6 Gy to induce double-strand breaks (DSBs), and DDR effects were assessed by 53BP1 or γH2AX foci resolution, cell survival, and senescence onset. Knockdown of TERT led to persistent DNA damage foci, confirming a role for TERT in DSB repair. Foci resolution was restored by WT TERT but not by the catalytic mutant TERT D712A, V713I. Similarly, the TERT R132E, K78E mutant, defective in TPP1 binding, exhibited persistent foci, implicating TERT-TPP1 interactions in DDR. Supporting this, TPP1 mutants unable to bind TERT also caused persistent DNA damage foci. Combined with evidence that shelterin complexes, including TPP1, localize rapidly to nontelomeric DSBs after DNA damage, these results suggest that TPP1 recruits TERT to DSBs, analogous to its role at telomeres. Ongoing studies aim to elucidate how TERT's catalytic activity promotes DSB repair and to explore TERT as a target for sensitizing cancer cells to therapy. Citation Format: Leon L. Zhou, Stephen J. Kron. Defining roles of telomerase reverse transcriptase in DNA damage response [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 4199.

Abstract International Agency for Cancer Research categorizes Helicobacter pylori as a Class I carcinogen for its known role in gastric cancers, especially among the low-income groups of developing countries where stomach infections are very common. Chronic infection caused by these bacteria results in gastric inflammation that trigger molecular events ultimately leading to cellular transformation. CagA, a pathogenic gene of H. pylori can disrupt multiple molecular targets in human cells and may also interrupt with normal cell proliferation and survival. This study demonstrates the carcinogenic potential of H. pylori by interfering with the function of telomeric complex and contributing to cellular immortality. GEO datasets were used to identify genes that are differentially expressed and how their altered expression compromised the normalcy of shelterin, CST, and TERT-TERC complexes. This study also explores the role of selected proteins that hampers the functioning of double stranded break (DSB) repair at telomeres. Finally, we compare standard and traditional drugs that may interfere with telomerase activity in cancer cells. We found that CagA may trigger the hTERT activation via the AKT-pathway. The target proteins Cdh1 and Pik3ca showed higher binding affinity with phytochemicals then with the standard of care drugs and possible play a role in indirectly inhibiting telomerase. Despite advancements in stomach cancer treatment, the findings from this study attempts to make a useful contribution in understanding H. pylori infection and resultant trigger of cancer hallmarks. Citation Format: Trupti Patel, Ujjayini Chakraborty. Identifying telomere-related molecular signatures in H. pylori infection and exploring plant-based potential telomerase inhibitors: An in-silico analysis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 5415.

Abstract The purpose of this study is to describe Chilean families having hereditary Gastric Cancer (GC) presenting pathogenic mutations in BRCA 2 (c.4740_4741dup NP_000050.3:p.Glu1581fs), ATM (c.3381_3384del NP_000042.3:p.Gln1128fs) and Protector of Telomers 1 (POT1, 1087C>T:p.Arg363Ter) genes. Only one hereditary diffuse GC (HDGC) Chilean family with a pathogenic CDH1 mutation has been reported, suggesting a low frequency of pathogenic mutation detection in this population. Whole exome sequencing (WES) was performed using the Agilent SureSelect Human All Exome V7 kit and sequenced in a NovaSeq6000 (Illumina, Inc.) S4 150PE aiming 100x. Alignment and variant calling were performed using Illumina Dragen v3.8. Variant calls were re-calibrated using GATK v4 variant recalibration and annotated with Illumina Nirvana and Annovar. Genotypification of the index patient and their family was performed using KASP-PCR. The index patient having a BRCA2 mutation had metastatic HDGC and his mother had asynchronous breast cancer and GC. The family presenting an ATM gene mutation had three GC-affected subjects, the index patient, and both parents. The index patient of the family having a POT1 mutation presented a CG at 47 yr., and two of her children died of CG at 24 yr. All families show an incomplete penetrance and variable expressivity. We are searching for the second hit in the index patient´s tumor samples. This is the first report of a POT1 gene mutation detected in a hereditary GC. POT1 belongs to the shelterin complex that protects telomeres. This mutation affects the binding to the shelterin complex, and it was previously reported in colorectal cancer. Beca Chile Postdoctorado 74190063, CONICYT-FONDAP 15130011 /ANID-FONDAP APOYO 1523A0008, NIH R01CA223978, R21CA199631, U54CA233306, and P30CA093373. Citation Format: Graciela Adriana Molina Fuentes, Ana Patricia Estrada-Florez, Paul Lott, Osvaldo Torres, Cedric Adelsdorfer, Alejandro H Corvalán, Luis Carvajal-Carmona. BRCA2, ATM, and POT1 genes mutations in Chilean hereditary gastric cancer families [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 1002.

Abstract Telomeres, nucleotide repeats and a six-protein complex called shelterin at chromosome ends, are critical for genomic integrity. Rare heterozygous pathogenic or likely pathogenic (P/LP) germline variants in shelterin complex genes have been associated with long telomeres and risk of certain cancers, including melanoma, lymphoproliferative diseases, glioma, papillary thyroid cancer, and sarcoma. Traditional phenotype-first studies of P/LP germline variants and disease are often limited by ascertainment of the most severely affected individuals. Genome-first approaches can reduce this bias by first assessing germline variants and then evaluating the associated diseases. Since most studies, to date, have focused on variants in POT1 and cancer, we sought to estimate associations between cancer and rare P/LP variants in the five less well studied shelterin genes (ACD, TERF1, TERF2, TERF2IP, and TINF2) in the UK Biobank (UKB) to understand their role in cancer etiology at the population level. Exome sequencing data on 469, 578 participants were retrieved from the UKB DNA Nexus platform. Variants with minor allele frequency <1%, exonic or splice site, genotype quality >30, depth >20, and allele fraction >0.3 were retained. Variant classification used Automated Germline Variant Pathogenicity (PMID: 38426335). Logistic regression analyses adjusted for age, sex, alcohol use, smoking, and BMI were used to calculate odds ratios (OR) and 95% confidence intervals (CI). There were 177 participants (97 female, 80 male, median age = 57.0 years, range = 40.0 - 69.0) with 59 unique P/LP germline variants (30 ACD, 9 TERF2, and 20 TINF2). Strikingly, there were no rare variants in TERF1 or TERF2IP. The population prevalence of individuals with P/LP germline variants in these five shelterin genes is estimated at 1:2, 514 (174/437, 486 unrelated individuals, 95% CI 2, 189-2, 953). Forty-eight individuals with P/LP germline variants were diagnosed with at least one cancer with a median age at first cancer of 59.3 years (range 19.4 - 80.6). Overall, P/LP variants were significantly associated with melanoma (OR 2.93, 95% CI 1.20-7.15, p = 0.018) and cancers of the urinary system (OR 2.78, 1.02-7.57, p = 0.045). By gene, P/LP variants were associated with cancers of the oral cavity/pharynx (ACD, OR 4.78, 95% CI 1.18-19.4, p = 0.030), soft tissue including heart (ACD, OR 8.90, 95% CI 1.24-63.9, p = 0.030), colon excluding the rectum (TERF2, OR 8.44 , 95%CI 1.05-68.0, p= 0.045), female genital system (TERF2, OR 12.98, 95% CI 1.43-117.8, p = 0.023), and melanoma (TINF2, OR 7.63, 2.35-24.75, p = 0.001).Rare P/LP germline variants in ACD, TERF2, and TINF2 may be associated with increased risk of certain cancers in the UKB. Analyses applying the genome-first approach other population-based cohorts and assessment of telomere length are underway to better understand the extent to which variation in shelterin genes contributes to cancer etiology. Citation Format: Akanksha Nagarkar, Hasset Nurelegne, Jung Kim, Kelvin C. de Andrade, Sharon A. Savage. Genome-first approach identifies shelterin complex gene variants and associated cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 4891.

Telomeres are the nucleoprotein structures at chromosome ends. Telomeres are particularly sensitive to oxidative stress, which can induce telomere damage, shortening, and premature cellular senescence. How oxidative damage influences telomere structure has not been defined. Here, we induce oxidative damage at telomeres using menadione, which damages mitochondria mimicking intrinsic oxidative stress. We find that oxidative stress induces at telomeres single-stranded DNA breaks, internal DNA loop structures, dissociation of the shelterin component TRF1, upregulation of TERRA long noncoding RNA, and increased DNA:RNA hybrid structures known as R-loops. R-loop formation is enhanced not only in cis at telomeres, which show increased TERRA transcription, but also in trans at telomeres at which TERRA transcription is not induced indicating post-transcriptional R-loop formation. Finally, we show that oxidative damage induced R-loop formation requires TRF2, whose R-loop promoting activity may be unleashed upon TRF1 dissociation from telomeres. Altogether, our findings uncover in response to oxidative stress major remodelling of telomeric DNA, RNA, and shelterin complexes, and they unravel a physiological role of TRF2’s ability to stimulate TERRA R-loop formation. We propose that the identified structural changes may facilitate DNA damage signalling and repair pathways to maintain telomere integrity during development and aging.

Telomeric repeats recruit the shelterin complex to prevent activation of the double-strand break response at chromosome ends. Thousands of TTAGGG repeats are present at each chromosome end to ensure telomere function. This abundance of G-rich repeats comes with the propensity to generate unusual DNA structures. The telomere loop (t-loop) structure, generated by strand invasion of the 3' overhang in the internal repeats, contributes to telomere function. G4-DNA is promoted by the stretches of G-rich repeats in a single-stranded form and may affect telomere replication and elongation by telomerase. The intramolecular homology can lead to the formation of internal loops (i-loops) via intramolecular recombination at sites of telomeric damage, which can promote the excision of telomeric repeats as extrachromosomal circular DNA. Shelterin promotes t-loops, counteracting the accumulation of pathological structures either directly or via the recruitment of specialized helicases. Here, we will discuss the current evidence for the formation of unusual DNA structures at telomeres and possible implications for telomere function.

Telomeres, the protective caps at the ends of chromosomes, play a crucial role in maintaining genomic stability. This review explores the structure and function of telomeres, the mechanisms of telomere shortening, and the role of telomerase in counteracting this process. Telomere shortening is a natural consequence of cell division and is associated with cellular aging, senescence, and apoptosis. The review delves into the molecular biology of telomeres, highlighting the significance of the shelterin complex in protecting telomeres from degradation and fusion. It also discusses the genetic and epigenetic factors influencing telomere length, the impact of oxidative stress and inflammation on telomere attrition, and potential interventions to preserve telomere length. The review concludes with recommendations for lifestyle changes and therapeutic strategies to mitigate telomere shortening and promote healthy aging.

TIN2 (TERF1 interacting nuclear factor 2) is a telomeric shelterin complex component, essential for telomere protection and early embryonic development in mammals. In humans, TIN2 isoforms arise from alternative splicing, but their specific roles in vivo remain unclear. Here, we explore TIN2 isoform functions in the laboratory mouse Mus musculus. Our comparative analysis of TIN2 protein sequences reveals that mouse TIN2 (TINF2) closely resembles the human TIN2L isoform, both of which harbor a C-terminal extended domain (CTED) absent from the human TIN2 small (TIN2S) isoform. To further characterize the functions of TIN2 isoforms, we generated a Tinf2 LD (long-form deficiency) allele in M. musculus encoding a short form of TINF2 lacking the CTED. Mice heterozygous or homozygous for this Tinf2 LD allele were viable, fertile, and showed no tissue abnormalities. Furthermore, protein product of Tinf2 LD allele localized to telomeres and maintained telomere integrity in mouse embryonic fibroblasts, demonstrating that the CTED is dispensable for telomere protection and normal development in mice. These findings indicate functional redundancy among TIN2 isoforms and underscore the utility of the Tinf2 LD model for uncovering isoform-specific mechanisms of telomere regulation.