Telomere-Associated Protein TIN2 Is Essential for Early Embryonic Development through a Telomerase-Independent Pathway

ABSTRACT TIN2 is a negative regulator of telomere elongation that interacts with telomeric DNA repeat binding factor 1 (TRF1) and affects telomere length by a telomerase-dependent mechanism. Here we show that inactivation of the mouse TRF1-interacting protein 2 (TIN2) gene results in early embryonic lethality. We further observed that the embryonic lethality of TIN2 mutant mice was not affected by inactivation of the telomerase reverse transcriptase gene, indicating that embryonic lethality is not the result of telomerase-dependent changes in telomere length or function. Our findings suggest that TIN2 has a role independent of telomere length regulation that is essential for embryonic development and cell viability.

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Telomere length regulation during cloning, embryogenesis and ageing

Reproduction Fertility and Development ◽

10.1071/rd04112 ◽

2005 ◽

Vol 17 (2) ◽

pp. 85 ◽

Cited By ~ 27

Author(s):

S. Schaetzlein ◽

K. L. Rudolph

Keyword(s):

Telomere Length ◽

Molecular Mechanisms ◽

De Novo ◽

Postnatal Life ◽

Bovine Embryos ◽

Telomeric Dna ◽

Cell Therapies ◽

Telomere Elongation ◽

Length Regulation ◽

Cloned Bovine

Telomeres are nucleoprotein complexes at the end of eukaryotic chromosomes with an essential role in chromosome capping. Owing to the end-replication problem of DNA polymerase, telomeres shorten during each cell division. When telomeres become critically short, they loose their capping function, which in turn induces a DNA damage-like response. This mechanism inhibits cell proliferation at the senescence stage and there is evidence that it limits the regenerative capacity of tissues and organs during chronic diseases and ageing. The holoenzyme telomerase synthesises telomeric DNA de novo, but, in humans, it is active only during embryogenesis, in immature germ cells and in a subset of stem/progenitor cells during postnatal life. Telomere length can be maintained or increased by telomerase, a process that appears to be regulated by a variety of telomere-binding proteins that control telomerase recruitment and activity at the telomeres. During embryogenesis, telomerase is strongly activated at the morula/blastocyst transition. At this transition, telomeres are significantly elongated in murine and bovine embryos. Early embryonic telomere elongation is telomerase dependent and leads to a rejuvenation of telomeres in cloned bovine embryos. Understanding of the molecular mechanisms underlying this early embryonic telomere elongation programme is of great interest for medical research in the fields of regeneration, cell therapies and therapeutic cloning.

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Control of Human Telomere Length by TRF1 and TRF2

Molecular and Cellular Biology ◽

10.1128/mcb.20.5.1659-1668.2000 ◽

2000 ◽

Vol 20 (5) ◽

pp. 1659-1668 ◽

Cited By ~ 486

Author(s):

Agata Smogorzewska ◽

Bas van Steensel ◽

Alessandro Bianchi ◽

Stefan Oelmann ◽

Matthias R. Schaefer ◽

...

Keyword(s):

Telomere Length ◽

Negative Regulator ◽

Loop Model ◽

Telomeric Dna ◽

Telomere Elongation ◽

Original Length ◽

Population Doublings ◽

Ttaggg Repeat

ABSTRACT Telomere length in human cells is controlled by a homeostasis mechanism that involves telomerase and the negative regulator of telomere length, TRF1 (TTAGGG repeat binding factor 1). Here we report that TRF2, a TRF1-related protein previously implicated in protection of chromosome ends, is a second negative regulator of telomere length. Overexpression of TRF2 results in the progressive shortening of telomere length, similar to the phenotype observed with TRF1. However, while induction of TRF1 could be maintained over more than 300 population doublings and resulted in stable, short telomeres, the expression of exogenous TRF2 was extinguished and the telomeres eventually regained their original length. Consistent with their role in measuring telomere length, indirect immunofluorescence indicated that both TRF1 and TRF2 bind to duplex telomeric DNA in vivo and are more abundant on telomeres with long TTAGGG repeat tracts. Neither TRF1 nor TRF2 affected the expression level of telomerase. Furthermore, the presence of TRF1 or TRF2 on a short linear telomerase substrate did not inhibit the enzymatic activity of telomerase in vitro. These findings are consistent with the recently proposed t loop model of telomere length homeostasis in which telomerase-dependent telomere elongation is blocked by sequestration of the 3′ telomere terminus in TRF1- and TRF2-induced telomeric loops.

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Cdc13 N-Terminal Dimerization, DNA Binding, and Telomere Length Regulation

Molecular and Cellular Biology ◽

10.1128/mcb.00515-10 ◽

2010 ◽

Vol 30 (22) ◽

pp. 5325-5334 ◽

Cited By ~ 23

Author(s):

Meghan T. Mitchell ◽

Jasmine S. Smith ◽

Mark Mason ◽

Sandy Harper ◽

David W. Speicher ◽

...

Keyword(s):

Dna Binding ◽

Telomere Length ◽

Functional Characterization ◽

Point Mutations ◽

Telomeric Dna ◽

Dna Binding Domains ◽

Binding Domains ◽

Length Regulation ◽

Telomere Length Regulation

ABSTRACT The essential yeast protein Cdc13 facilitates chromosome end replication by recruiting telomerase to telomeres, and together with its interacting partners Stn1 and Ten1, it protects chromosome ends from nucleolytic attack, thus contributing to genome integrity. Although Cdc13 has been studied extensively, the precise role of its N-terminal domain (Cdc13N) in telomere length regulation remains unclear. Here we present a structural, biochemical, and functional characterization of Cdc13N. The structure reveals that this domain comprises an oligonucleotide/oligosaccharide binding (OB) fold and is involved in Cdc13 dimerization. Biochemical data show that Cdc13N weakly binds long, single-stranded, telomeric DNA in a fashion that is directly dependent on domain oligomerization. When introduced into full-length Cdc13 in vivo, point mutations that prevented Cdc13N dimerization or DNA binding caused telomere shortening or lengthening, respectively. The multiple DNA binding domains and dimeric nature of Cdc13 offer unique insights into how it coordinates the recruitment and regulation of telomerase access to the telomeres.

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Yeast Est2p Affects Telomere Length by Influencing Association of Rap1p with Telomeric Chromatin

Molecular and Cellular Biology ◽

10.1128/mcb.01648-07 ◽

2008 ◽

Vol 28 (7) ◽

pp. 2380-2390 ◽

Cited By ~ 11

Author(s):

Hong Ji ◽

Christopher J. Adkins ◽

Bethany R. Cartwright ◽

Katherine L. Friedman

Keyword(s):

Saccharomyces Cerevisiae ◽

Telomere Length ◽

Specific Binding ◽

Telomerase Activity ◽

Negative Regulator ◽

Wild Type ◽

Telomeric Dna ◽

Telomere Length Homeostasis

ABSTRACT In Saccharomyces cerevisiae, the sequence-specific binding of the negative regulator Rap1p provides a mechanism to measure telomere length: as the telomere length increases, the binding of additional Rap1p inhibits telomerase activity in cis. We provide evidence that the association of Rap1p with telomeric DNA in vivo occurs in part by sequence-independent mechanisms. Specific mutations in EST2 (est2-LT) reduce the association of Rap1p with telomeric DNA in vivo. As a result, telomeres are abnormally long yet bind an amount of Rap1p equivalent to that observed at wild-type telomeres. This behavior contrasts with that of a second mutation in EST2 (est2-up34) that increases bound Rap1p as expected for a strain with long telomeres. Telomere sequences are subtly altered in est2-LT strains, but similar changes in est2-up34 telomeres suggest that sequence abnormalities are a consequence, not a cause, of overelongation. Indeed, est2-LT telomeres bind Rap1p indistinguishably from the wild type in vitro. Taken together, these results suggest that Est2p can directly or indirectly influence the binding of Rap1p to telomeric DNA, implicating telomerase in roles both upstream and downstream of Rap1p in telomere length homeostasis.

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A RAP1-interacting protein involved in transcriptional silencing and telomere length regulation

Trends in Genetics ◽

10.1016/0168-9525(92)90388-k ◽

1992 ◽

Vol 8 (7) ◽

pp. 231

Keyword(s):

Telomere Length ◽

Transcriptional Silencing ◽

Interacting Protein ◽

Length Regulation ◽

Telomere Length Regulation

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The Role of Rif1 in telomere length regulation is separable from its role in origin firing

10.1101/2020.04.24.060491 ◽

2020 ◽

Author(s):

Calla B. Shubin ◽

Carol W. Greider

Keyword(s):

Telomere Length ◽

Protein Phosphatase ◽

Protein Phosphatase 1 ◽

Origin Firing ◽

Replication Complex ◽

Telomere Elongation ◽

Length Regulation ◽

Telomere Length Regulation ◽

Telomere Lengthening

AbstractTo examine the established link between DNA replication and telomere length, we tested whether firing of telomeric origins would cause telomere lengthening. We found that RIF1 mutants that block Protein Phosphatase 1 (PP1) binding activated telomeric origins but did not elongate telomeres. In a second approach, we found overexpression of ΔN-Dbf4 and Cdc7 increased DDK activity and activated telomeric origins, yet telomere length was unchanged. We tested a third mechanism to activate origins using the sld3-A mcm5-bob1 mutant that deregulates the pre-replication complex, and again saw no change in telomere length. Finally, we tested whether mutations in RIF1 that cause telomere elongation would affect origin firing. We found that neither rif1-Δ1322 nor rif1HOOK affected firing of telomeric origins. We conclude that telomeric origin firing does not cause telomere elongation, and the role of Rif1 in regulating origin firing is separable from its role in regulating telomere length.

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Telomeres and Cancer

Life ◽

10.3390/life11121405 ◽

2021 ◽

Vol 11 (12) ◽

pp. 1405

Author(s):

Hueng-Chuen Fan ◽

Fung-Wei Chang ◽

Jeng-Dau Tsai ◽

Kao-Min Lin ◽

Chuan-Mu Chen ◽

...

Keyword(s):

Telomere Length ◽

Molecular Mechanisms ◽

Telomere Maintenance ◽

Cancer Development ◽

Telomere Elongation ◽

Metabolism Pathway ◽

Length Regulation ◽

Telomere Length Regulation ◽

Genome Protection

Telomeres cap the ends of eukaryotic chromosomes and are indispensable chromatin structures for genome protection and replication. Telomere length maintenance has been attributed to several functional modulators, including telomerase, the shelterin complex, and the CST complex, synergizing with DNA replication, repair, and the RNA metabolism pathway components. As dysfunctional telomere maintenance and telomerase activation are associated with several human diseases, including cancer, the molecular mechanisms behind telomere length regulation and protection need particular emphasis. Cancer cells exhibit telomerase activation, enabling replicative immortality. Telomerase reverse transcriptase (TERT) activation is involved in cancer development through diverse activities other than mediating telomere elongation. This review describes the telomere functions, the role of functional modulators, the implications in cancer development, and the future therapeutic opportunities.

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The role of Rif1 in telomere length regulation is separable from its role in origin firing

eLife ◽

10.7554/elife.58066 ◽

2020 ◽

Vol 9 ◽

Cited By ~ 1

Author(s):

Calla B Shubin ◽

Carol W Greider

Keyword(s):

Telomere Length ◽

Protein Phosphatase ◽

Protein Phosphatase 1 ◽

Origin Firing ◽

Replication Complex ◽

Telomere Elongation ◽

Length Regulation ◽

Telomere Length Regulation ◽

Telomere Lengthening

To examine the established link between DNA replication and telomere length, we tested whether firing of telomeric origins would cause telomere lengthening. We found that RIF1 mutants that block Protein Phosphatase 1 (PP1) binding activated telomeric origins but did not elongate telomeres. In a second approach, we found overexpression of ∆N-Dbf4 and Cdc7 increased DDK activity and activated telomeric origins, yet telomere length was unchanged. We tested a third mechanism to activate origins using the sld3-A mcm5-bob1 mutant that de-regulates the pre-replication complex, and again saw no change in telomere length. Finally, we tested whether mutations in RIF1 that cause telomere elongation would affect origin firing. We found that neither rif1-∆1322 nor rif1HOOK affected firing of telomeric origins. We conclude that telomeric origin firing does not cause telomere elongation, and the role of Rif1 in regulating origin firing is separable from its role in regulating telomere length.

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Murine Pif1 Interacts with Telomerase and Is Dispensable for Telomere Function In Vivo

Molecular and Cellular Biology ◽

10.1128/mcb.01866-06 ◽

2006 ◽

Vol 27 (3) ◽

pp. 1017-1026 ◽

Cited By ~ 48

Author(s):

Bryan E. Snow ◽

Maria Mateyak ◽

Jana Paderova ◽

Andrew Wakeham ◽

Caterina Iorio ◽

...

Keyword(s):

Telomere Length ◽

Chromosomal Rearrangements ◽

Dna Helicase ◽

Negative Regulator ◽

Wild Type ◽

Genetic Redundancy ◽

Telomeric Dna ◽

Dna Helicases

ABSTRACT Pif1 is a 5′-to-3′ DNA helicase critical to DNA replication and telomere length maintenance in the budding yeast Saccharomyces cerevisiae. ScPif1 is a negative regulator of telomeric repeat synthesis by telomerase, and recombinant ScPif1 promotes the dissociation of the telomerase RNA template from telomeric DNA in vitro. In order to dissect the role of mPif1 in mammals, we cloned and disrupted the mPif1 gene. In wild-type animals, mPif1 expression was detected only in embryonic and hematopoietic lineages. mPif1 − / − mice were viable at expected frequencies, displayed no visible abnormalities, and showed no reproducible alteration in telomere length in two different null backgrounds, even after several generations. Spectral karyotyping of mPif1 − / − fibroblasts and splenocytes revealed no significant change in chromosomal rearrangements. Furthermore, induction of apoptosis or DNA damage revealed no differences in cell viability compared to what was found for wild-type fibroblasts and splenocytes. Despite a novel association of mPif1 with telomerase, mPif1 did not affect the elongation activity of telomerase in vitro. Thus, in contrast to what occurs with ScPif1, murine telomere homeostasis or genetic stability does not depend on mPif1, perhaps due to fundamental differences in the regulation of telomerase and/or telomere length between mice and yeast or due to genetic redundancy with other DNA helicases.

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