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Setting boundaries for genome-wide heterochromatic DNA deletions through flanking inverted repeats in Tetrahymena thermophila.

ABSTRACT: Eukaryotic cells pack their genomic DNA into euchromatin and heterochromatin. Boundaries between these domains have been shown to be set by boundary elements. In Tetrahymena, heterochromatin domains are targeted for deletion from the somatic nuclei through a sophisticated programmed DNA rearrangement mechanism, resulting in the elimination of 34% of the germline genome in ?10,000 dispersed segments. Here we showed that most of these deletions occur consistently with very limited variations in their boundaries among inbred lines. We identified several potential flanking regulatory sequences, each associated with a subset of deletions, using a genome-wide motif finding approach. These flanking sequences are inverted repeats with the copies located at nearly identical distances from the opposite ends of the deleted regions, suggesting potential roles in boundary determination. By removing and testing two such inverted repeats in vivo, we found that the ability for boundary maintenance of the associated deletion were lost. Furthermore, we analyzed the deletion boundaries in mutants of a known boundary-determining protein, Lia3p and found that the subset of deletions that are affected by LIA3 knockout contained common features of flanking regulatory sequences. This study suggests a common mechanism for setting deletion boundaries by flanking inverted repeats in Tetrahymena thermophila.

SUBMITTER: Lin CG

PROVIDER: S-EPMC6547420 | biostudies-literature | 2019 Jun

REPOSITORIES: biostudies-literature

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A small family of elements with long inverted repeats is located near sites of developmentally regulated DNA rearrangement in Tetrahymena thermophila.

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Genome-Wide gene expression of Tetrahymena thermophila conjugation

Project description:Eleven genome wide microarrays containing the predicted coding sequences (putative genes) for the ciliated protozoan Tetrahymena thermophila used to study gene expression in conjugation cells (C-0, C-15m, C-2, C-4, C-6, C-8, C-10, C-12, C-14, C-16, C-18). Combined these eleven microarrays with 50 microarrays described in Miao et al (2009) and other 6 microarrays, we constructed the Tetrahymena gene network (TGN) using three methods: the Pearson correlation coefficient, the Spearman correlation coefficient and the context likelihood of relatedness (CLR) algorithm. The accuracy and coverage of the three networks were evaluated using four conserved protein complexes in yeast, and the CLR network was found to be the best network, with a Z-score threshold 3.49. Then the TGN was partitioned, and 55 modules were found. In addition, analysis for the arbitrarily determined 1200 hubs showed that these hubs could be sorted into six groups according to expression profiles. We also investigated human disease orthologs in Tetrahymena that are missing in yeast and found evidence indicating that some of these were involved in the same process in Tetrahymena as in human.

2011-06-13 | GSE26650 | GEO

Genome-Wide gene expression of Tetrahymena thermophila conjugation

2011-06-13 | E-GEOD-26650 | biostudies-arrayexpress

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A Parallel G Quadruplex-Binding Protein Regulates the Boundaries of DNA Elimination Events of Tetrahymena thermophila.

Project description:Guanine (G)-rich DNA readily forms four-stranded quadruplexes in vitro, but evidence for their participation in genome regulation is limited. We have identified a quadruplex-binding protein, Lia3, that controls the boundaries of germline-limited, internal eliminated sequences (IESs) of Tetrahymena thermophila. Differentiation of this ciliate's somatic genome requires excision of thousands of IESs, targeted for removal by small-RNA-directed heterochromatin formation. In cells lacking LIA3 (?LIA3), the excision of IESs bounded by specific G-rich polypurine tracts was impaired and imprecise, whereas the removal of IESs without such controlling sequences was unaffected. We found that oligonucleotides containing these polypurine tracts formed parallel G-quadruplex structures that are specifically bound by Lia3. The discovery that Lia3 binds G-quadruplex DNA and controls the accuracy of DNA elimination at loci with specific G-tracts uncovers an unrecognized potential of quadruplex structures to regulate chromosome organization.

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Inverted low-copy repeats and genome instability--a genome-wide analysis.

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