STN1 protects chromosome ends in Arabidopsis thaliana

Abstract

Telomeres shield the natural ends of chromosomes from nucleolytic attack, recognition as double-strand breaks, and inappropriate processing by DNA repair machinery. The trimeric Stn1/Ten1/ Cdc13 complex is critical for chromosome end protection in Saccharomyces cerevisiae, while vertebrate telomeres are protected by shelterin, a complex of six proteins that does not include STN1 or TEN1. Recent studies demonstrate that Stn1 and Ten1 orthologs in Schizosaccharomyces pombe contribute to telomere integrity in a complex that is distinct from the shelterin components, Pot1 and Tpp1. Thus, chromosome-end protection may be mediated by distinct subcomplexes of telomere proteins. Here we report the identification of a STN1 gene in Arabidopsis that is essential for chromosome-end protection. AtSTN1 encodes an 18-kDa protein bearing a single oligonucleotide/oligosaccharide binding fold with significant sequence similarity to the yeast Stn1 proteins. Plants null for AtSTN1 display an immediate onset of growth and developmental defects and reduced fertility. These outward phenotypes are accompanied by catastrophic loss of telomeric and subtelomeric DNA, high levels of end-to-end chromosome fusions, increased G-overhang signals, and elevated telomere recombination. Thus, AtSTN1 is a crucial component of the protective telomere cap in Arabidopsis, and likely in other multicellular eukaryotes.telomere ͉ anaphase bridges ͉ oligonucleotide/oligosaccharide binding fold ͉ G-overhang

Human TEN1 Maintains Telomere Integrity and Functions in Genome-wide Replication Restart

“…Moreover, co-overexpression of Stn1 and Ten1 is sufficient to provide telomere protection in the absence of Cdc13, again suggesting the existence of a functional Stn1-Ten1 subcomplex (43). In Arabidopsis, CTC1 localizes to ϳ50% of telomeres, whereas TEN1 is only found at 10 -15% (44,45). This finding suggests the existence of CTC1 subcomplexes that do not contain TEN1.…”

“…This finding suggests the existence of CTC1 subcomplexes that do not contain TEN1. Additionally, Arabidopsis TEN1 inhibits telomerase processivity, whereas CTC1 and STN1 have no effect (29,44,45). Here we show that depletion of TEN1 leads to phenotypes similar to those seen after CTC1 or STN1 depletion; however, the severity of a subset of phenotypes is enhanced.…”

Human Stn1 protects telomere integrity by promoting efficient lagging-strand synthesis at telomeres and mediating C-strand fill-in

“…In yeasts and plants, homologs of CST appear to ensure telomere stability by capping chromosome ends [3,[11][12][13][14][15][16][17][18][19][20][21][22]. In vertebrates, the capping function is achieved by shelterin proteins.…”

“…In plants, Ctc1/ Stn1/Ten1 plays a major role in chromosome end protection. Ctc1-and Stn1-null mutants in Arabidopsis suffer dramatic telomere shortening, end-to-end chromosomal fusions, increased G-overhangs, and elevated extrachromosomal telomeric circles [3,12].…”

“…In yeasts and plants, homologs of CST are critical for ensuring telomere stability [3,[11][12][13][14][15][16][17][18][19][20][21][22]. In budding yeast, the Cdc13/Stn1/Ten1 complex associates exclusively with the G-overhang and plays important roles in restricting excessive C-strand resection from telomere ends, mediating C-strand fill-in, and regulating telomerase activity [14][15][16][17][18][19][20][21][22].…”