The integrity of eukaryote genomes is derived in part from telomeres, the specialized nucleoprotein complexes that physically cap the chromosome terminus to distinguish it from a double-strand break to facilitate its complete replication. Loss of essential capping proteins or the telomere maintenance enzyme, telomerase, results in activation of DNA damage checkpoints and end-to-end chromosome fusions that culminate in massive genome instability. Defects in telomerase and/or telomere maintenance lead to proliferation-related human diseases, while correct telomerase regulation is essential to impede carcinogenesis. Elucidating how constituents of the telomere complex safeguard the genome is essential for understanding mechanisms that underlie human disease. Here we propose to exploit the many advantages of the Arabidopsis model system to investigate essential components of the telomere cap in a genetically tractable higher eukaryote. The prevailing view has been that telomeres are capped by two distinct complexes, shelterin in vertebrates and CST (Cdc13, Stn1, Ten1) in yeast. In the previous funding period, we discovered a new telomere complex in Arabidopsis comprised of STN1 and TEN1 orthologs and a novel telomere protein, CTC1. This new CST complex is required for telomere integrity in both plants and humans. The plant and human CTC1 orthologs share the same overall domain structure and non-specific ssDNA binding, distinct from yeast Cdc13. However, Arabidopsis CST plays a more pivotal role in chromosome end protection, akin to yeast CST. Thus, studies of Arabidopsis CST may provide a critical evolutionary bridge to elucidate mechanisms of telomere replication and chromosome end protection in higher eukaryotes. The central hypothesis of this renewal application that CTC1 is a multifunctional scaffold that protects chromosome ends and promotes telomeric DNA replication.
Aim 1 will investigate interactions within the CST complex and explore the functional relevance of the TEN1- STN1 association for chromosome end protection.
Aim 2 will assess the role of CST in telomere protection versus telomeric DNA replication.
Aim 3 will test the hypothesis that POT1a recruits telomerase to the chromosome terminus via interactions with CTC1 and TER1. Finally, Aim 4 will employ forward genetic approaches and an innovative genetic screen possible only in Arabidopsis to isolate shelterin and CST- interacting factors and new telomere proteins. The studies will help to reconcile how CST and shelterin work together to promote telomere integrity. Altogether, the results generated from these four Aims will synergize to yield a much broader understanding of how telomeres stabilize higher eukaryotic genomes.

Public Health Relevance

Telomeres are essential for genome integrity and as a consequence, understanding how the telomere complex safeguards genome stability will be crucial for elucidating the fundamental mechanisms that regulate cell proliferation and impede carcinogenesis. Studies in model organisms have established the paradigms for human telomere biology, and continue to uncover novel telomere components and regulatory mechanisms. In this tradition, we will exploit the genetic tractability of Arabidopsis and its extraordinary tolerance to telomere dysfunction to investigate a new telomere capping complex in multicellular organisms.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM065383-11
Application #
8390480
Study Section
Nuclear and Cytoplasmic Structure/Function and Dynamics Study Section (NCSD)
Program Officer
Carter, Anthony D
Project Start
2002-05-01
Project End
2014-11-30
Budget Start
2012-12-01
Budget End
2013-11-30
Support Year
11
Fiscal Year
2013
Total Cost
$321,778
Indirect Cost
$95,003
Name
Texas A&M University
Department
Biochemistry
Type
Schools of Earth Sciences/Natur
DUNS #
078592789
City
College Station
State
TX
Country
United States
Zip Code
77845
Lee, Jung Ro; Xie, Xiaoyuan; Yang, Kailu et al. (2016) Dynamic interactions of Arabidopsis TEN1: stabilizing telomeres in response to heat stress. Plant Cell :
Nelson, Andrew D L; Shippen, Dorothy E (2015) Evolution of TERT-interacting lncRNAs: expanding the regulatory landscape of telomerase. Front Genet 6:277
González-García, Mary-Paz; Pavelescu, Irina; Canela, Andrés et al. (2015) Single-cell telomere-length quantification couples telomere length to meristem activity and stem cell development in Arabidopsis. Cell Rep 11:977-89
Beilstein, Mark A; Renfrew, Kyle B; Song, Xiangyu et al. (2015) Evolution of the Telomere-Associated Protein POT1a in Arabidopsis thaliana Is Characterized by Positive Selection to Reinforce Protein-Protein Interaction. Mol Biol Evol 32:1329-41
Boltz, Kara A; Jasti, Madhu; Townley, Jennifer M et al. (2014) Analysis of poly(ADP-Ribose) polymerases in Arabidopsis telomere biology. PLoS One 9:e88872
Renfrew, Kyle B; Song, Xiangyu; Lee, Jung Ro et al. (2014) POT1a and components of CST engage telomerase and regulate its activity in Arabidopsis. PLoS Genet 10:e1004738
Leehy, Katherine A; Lee, Jung Ro; Song, Xiangyu et al. (2013) MERISTEM DISORGANIZATION1 encodes TEN1, an essential telomere protein that modulates telomerase processivity in Arabidopsis. Plant Cell 25:1343-54
Shakirov, Eugene V; Shippen, Dorothy E (2012) Selaginella moellendorffii telomeres: conserved and unique features in an ancient land plant lineage. Front Plant Sci 3:161
Nelson, Andrew D L; Shippen, Dorothy E (2012) Blunt-ended telomeres: an alternative ending to the replication and end protection stories. Genes Dev 26:1648-52
Cifuentes-Rojas, Catherine; Nelson, Andrew D L; Boltz, Kara A et al. (2012) An alternative telomerase RNA in Arabidopsis modulates enzyme activity in response to DNA damage. Genes Dev 26:2512-23

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