Dataset Information

A non-canonical function of zebrafish telomerase reverse transcriptase is required for developmental hematopoiesis.

ABSTRACT: Although it is clear that telomerase expression is crucial for the maintenance of telomere homeostasis, there is increasing evidence that the TERT protein can have physiological roles that are independent of this central function. To further examine the role of telomerase during vertebrate development, the zebrafish telomerase reverse transcriptase (zTERT) was functionally characterized. Upon zTERT knockdown, zebrafish embryos show reduced telomerase activity and are viable, but develop pancytopenia resulting from aberrant hematopoiesis. The blood cell counts in TERT-depleted zebrafish embryos are markedly decreased and hematopoietic cell differentiation is impaired, whereas other somatic lineages remain morphologically unaffected. Although both primitive and definitive hematopoiesis is disrupted by zTERT knockdown, the telomere lengths are not significantly altered throughout early development. Induced p53 deficiency, as well as overexpression of the anti-apoptotic proteins Bcl-2 and E1B-19K, significantly relieves the decreased blood cells numbers caused by zTERT knockdown, but not the impaired blood cell differentiation. Surprisingly, only the reverse transcriptase motifs of zTERT are crucial, but the telomerase RNA-binding domain of zTERT is not required, for rescuing complete hematopoiesis. This is therefore the first demonstration of a non-canonical catalytic activity of TERT, which is different from "authentic" telomerase activity, is required for during vertebrate hematopoiesis. On the other hand, zTERT deficiency induced a defect in hematopoiesis through a potent and specific effect on the gene expression of key regulators in the absence of telomere dysfunction. These results suggest that TERT non-canonically functions in hematopoietic cell differentiation and survival in vertebrates, independently of its role in telomere homeostasis. The data also provide insights into a non-canonical pathway by which TERT functions to modulate specification of hematopoietic stem/progenitor cells during vertebrate development. (276 words).

SUBMITTER: Imamura S

PROVIDER: S-EPMC2561060 | biostudies-literature | 2008

REPOSITORIES: biostudies-literature

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A non-canonical function of zebrafish telomerase reverse transcriptase is required for developmental hematopoiesis.

Imamura Shintaro S Uchiyama Junzo J Koshimizu Eriko E Hanai Jun-Ichi J Raftopoulou Christina C Murphey Ryan D RD Bayliss Peter E PE Imai Yoichi Y Burns Caroline Erter CE Masutomi Kenkichi K Gagos Sarantis S Zon Leonard I LI Roberts Thomas M TM Kishi Shuji S

PloS one 20081010 10

Although it is clear that telomerase expression is crucial for the maintenance of telomere homeostasis, there is increasing evidence that the TERT protein can have physiological roles that are independent of this central function. To further examine the role of telomerase during vertebrate development, the zebrafish telomerase reverse transcriptase (zTERT) was functionally characterized. Upon zTERT knockdown, zebrafish embryos show reduced telomerase activity and are viable, but develop pancytop ...[more]

PMID: 18846223

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Project description:Background: Calcific aortic valve disease (CAVD) is the pathological remodeling of valve leaflets. The initial steps in the osteogenic reprogramming of the leaflet are not fully understood. Studies have shown that TERT overexpression primes mesenchymal stem cells to differentiate into osteoblasts, and we investigated whether TERT contributes to the osteogenic reprogramming of valve interstitial cells (VICs). Methods: Human control and CAVD aortic valve leaflets and patient-specific hVICs were used in in vivo and in vitro calcification assays. Loss of function experiments in hVICs and cells isolated from Tert-/- and Terc-/- mice were used for mechanistic studies. In silico modeling, proximity ligation and co-immunoprecipitation assays defined novel TERT interacting partners. Chromatin immunoprecipitation and CUT&TAG sequencing defined protein-DNA interactions. Results: TERT protein was highly expressed in calcified valve leaflets without changes in telomere length, DNA damage, or senescence markers, and these features were retained in isolated primary hVICs. TERT expression increased with osteogenic stimuli, while knock-down or genetic deletion of TERT prevented calcification. Mechanistically, TERT was required to initiate osteogenic reprogramming independent of its canonical telomere-extending activity and the lncRNA TERC. TERT’s osteogenic functions via binding with Signal Transducer and Activator of Transcription 5 (STAT5). Depletion and inhibition of STAT5 prevented calcification. STAT5 was found to bind the promoter region of Runt-Related Transcription Factor 2 (RUNX2), the master regulator of osteogenic reprogramming. Finally, we demonstrate that TERT and STAT5 are upregulated and colocalized in CAVD tissue. Conclusions: TERT's non-canonical activity is required to initiate VIC calcification. TERT partners with STAT5 to bind the RUNX2 gene promoter. These data identify a novel mechanism and potential therapeutic target to decrease vascular calcification.

Project description:BackgroundTelomerase is a reverse transcriptase that maintains the telomeres of linear chromosomes and preserves genomic integrity. The core components are a catalytic protein subunit, the telomerase reverse transcriptase (TERT), and an RNA subunit, the telomerase RNA (TR). Telomerase is unique in its ability to catalyze processive DNA synthesis, which is facilitated by telomere-specific DNA-binding domains in TERT called anchor sites. A conserved glutamine residue in the TERT N-terminus is important for anchor site interactions in lower eukaryotes. The significance of this residue in higher eukaryotes, however, has not been investigated.Methodology/principal findingsTo understand the significance of this residue in higher eukaryotes, we performed site-directed mutagenesis on human TERT (hTERT) Q169 to create neutral (Q169A), conservative (Q169N), and non-conservative (Q169D) mutant proteins. We show that these mutations severely compromise telomerase activity in vitro and in vivo. The functional defects are not due to abrogated interactions with hTR or telomeric ssDNA. However, substitution of hTERT Q169 dramatically impaired the ability of telomerase to incorporate nucleotides at the second position of the template. Furthermore, Q169 mutagenesis altered the relative strength of hTERT-telomeric ssDNA interactions, which identifies Q169 as a novel residue in hTERT required for optimal primer binding. Proteolysis experiments indicate that Q169 substitution alters the protease-sensitivity of the hTERT N-terminus, indicating that a conformational change in this region of hTERT is likely critical for catalytic function.Conclusions/significanceWe provide the first detailed evidence regarding the biochemical and cellular roles of an evolutionarily-conserved Gln residue in higher eukaryotes. Collectively, our results indicate that Q169 is needed to maintain the hTERT N-terminus in a conformation that is necessary for optimal enzyme-primer interactions and nucleotide incorporation. We show that Q169 is critical for the structure and function of human telomerase, thereby identifying a novel residue in hTERT that may be amenable to therapeutic intervention.

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A non-canonical function of zebrafish telomerase reverse transcriptase is required for developmental hematopoiesis.

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A non-canonical function of zebrafish telomerase reverse transcriptase is required for developmental hematopoiesis.

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