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The Analysis of Pendolino (peo) Mutants Reveals Differences in the Fusigenic Potential among Drosophila Telomeres.

Cenci G, Ciapponi L, Marzullo M, Raffa GD, Morciano P, Raimondo D, Burla R, Saggio I, Gatti M - PLoS Genet. (2015)

Bottom Line: The Peo protein directly interacts with the terminin components, but peo mutations do not affect telomeric localization of HOAP, Moi, Ver and HP1a, suggesting that the peo-dependent telomere fusion phenotype is not due to loss of terminin from chromosome ends. peo mutants are also defective in DNA replication and PCNA recruitment.However, our results suggest that general defects in DNA replication are unable to induce TFs in Drosophila cells.We thus hypothesize that DNA replication in Peo-depleted cells results in specific fusigenic lesions concentrated in heterochromatin-associated telomeres.

View Article: PubMed Central - PubMed

Affiliation: Dipartimento di Biologia e Biotecnologie, Sapienza-Università di Roma, Roma, Italy; Istituto Pasteur Fondazione Cenci Bolognetti, Sapienza-Università di Roma, Roma, Italy.

ABSTRACT
Drosophila telomeres are sequence-independent structures that are maintained by transposition to chromosome ends of three specialized retroelements (HeT-A, TART and TAHRE; collectively designated as HTT) rather than telomerase activity. Fly telomeres are protected by the terminin complex (HOAP-HipHop-Moi-Ver) that localizes and functions exclusively at telomeres and by non-terminin proteins that do not serve telomere-specific functions. Although all Drosophila telomeres terminate with HTT arrays and are capped by terminin, they differ in the type of subtelomeric chromatin; the Y, XR, and 4L HTT are juxtaposed to constitutive heterochromatin, while the XL, 2L, 2R, 3L and 3R HTT are linked to the TAS repetitive sequences; the 4R HTT is associated with a chromatin that has features common to both euchromatin and heterochromatin. Here we show that mutations in pendolino (peo) cause telomeric fusions (TFs). The analysis of several peo mutant combinations showed that these TFs preferentially involve the Y, XR and 4th chromosome telomeres, a TF pattern never observed in the other 10 telomere-capping mutants so far characterized. peo encodes a non-terminin protein homologous to the E2 variant ubiquitin-conjugating enzymes. The Peo protein directly interacts with the terminin components, but peo mutations do not affect telomeric localization of HOAP, Moi, Ver and HP1a, suggesting that the peo-dependent telomere fusion phenotype is not due to loss of terminin from chromosome ends. peo mutants are also defective in DNA replication and PCNA recruitment. However, our results suggest that general defects in DNA replication are unable to induce TFs in Drosophila cells. We thus hypothesize that DNA replication in Peo-depleted cells results in specific fusigenic lesions concentrated in heterochromatin-associated telomeres. Alternatively, it is possible that Peo plays a dual function being independently required for DNA replication and telomere capping.

No MeSH data available.


Related in: MedlinePlus

Structure of Drosophila telomeres and subtelomeres.Schematic representation of Drosophila chromosome ends. From a distal to a proximal direction chromosome ends contain the terminin-associated region (red) that may extend for approximately 10 Kb (22), the HTT array that vary in length from 26 to 147 Kb [81] and may either repress (dark blue) or not repress (light blue) the expression of transgenes; the TAS sequences (light green) that comprise about 20 Kb [55, 81], or different types of chromatin: constitutive heterochromatin (Het, grey), or the 4th chromosome chromatin (4-ch, dark green) that has distinctive properties as well as properties shared by euchromatin and heterochromatin. The repressive properties of the YL, XR and 4L HTT have been inferred from those of the YS HTT; the properties of XL and 2L HTT are inferred from those 2L, 3L and 3R HTT. See text for detailed explanation.
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pgen.1005260.g012: Structure of Drosophila telomeres and subtelomeres.Schematic representation of Drosophila chromosome ends. From a distal to a proximal direction chromosome ends contain the terminin-associated region (red) that may extend for approximately 10 Kb (22), the HTT array that vary in length from 26 to 147 Kb [81] and may either repress (dark blue) or not repress (light blue) the expression of transgenes; the TAS sequences (light green) that comprise about 20 Kb [55, 81], or different types of chromatin: constitutive heterochromatin (Het, grey), or the 4th chromosome chromatin (4-ch, dark green) that has distinctive properties as well as properties shared by euchromatin and heterochromatin. The repressive properties of the YL, XR and 4L HTT have been inferred from those of the YS HTT; the properties of XL and 2L HTT are inferred from those 2L, 3L and 3R HTT. See text for detailed explanation.

Mentions: All Drosophila chromosomes of wild type strains terminate with HTT arrays of variable length (made of complete and incomplete HeT-A, TART and TAHRE elements) (reviewed in [5, 52, 53]) and are capped by the multiprotein terminin complex (reviewed in [6]). However Drosophila telomeres differ from each other in both the type of subtelomeric chromatin and in the properties of their HTT arrays (Fig 12). One of the most straightforward features that contradistinguish some of the Drosophila telomeres is their association with constitutive hetrochromatin. Approximately one-third of the Drosophila genome is made of constitutive heterochromatin; the entire Y chromosome, the short arm (XR) and the proximal 40% of the long arm (XL) of the X chromosome, the short arm (4L) and the proximal 70% of the long arm (4R) of the 4th chromosome, and the centric 25% of chromosomes 2 and 3 are heterochromatic [38, 54]. Thus the HTT arrays of YL, YS, XR and 4L are linked to constitutive heterochromatin (Fig 12). The HHT blocks of XL and those of the major autosomes are not directly associated with euchromatin but are instead juxtaposed to divergent clusters of subtelomeric repeats, known as telomere associated sequences (TAS) (reviewed in [55]). The TAS are not only different in sequence but are also occasionally absent from the subtelomeric regions, suggesting that their presence is not essential for proper telomere function [55]. Finally, the 4R telomere is joined to a special type of chromatin that has peculiar features, as well as features shared with both euchromatin and heterochromatin; for example the 4R distal chromatin is enriched in the 4th chromosome-specific Painting of four (Pof) protein and the heterochromatic markers HP1a and histone 3 methylated at lysine 9 (H3K9) (reviewed in [56]) (Fig 12).


The Analysis of Pendolino (peo) Mutants Reveals Differences in the Fusigenic Potential among Drosophila Telomeres.

Cenci G, Ciapponi L, Marzullo M, Raffa GD, Morciano P, Raimondo D, Burla R, Saggio I, Gatti M - PLoS Genet. (2015)

Structure of Drosophila telomeres and subtelomeres.Schematic representation of Drosophila chromosome ends. From a distal to a proximal direction chromosome ends contain the terminin-associated region (red) that may extend for approximately 10 Kb (22), the HTT array that vary in length from 26 to 147 Kb [81] and may either repress (dark blue) or not repress (light blue) the expression of transgenes; the TAS sequences (light green) that comprise about 20 Kb [55, 81], or different types of chromatin: constitutive heterochromatin (Het, grey), or the 4th chromosome chromatin (4-ch, dark green) that has distinctive properties as well as properties shared by euchromatin and heterochromatin. The repressive properties of the YL, XR and 4L HTT have been inferred from those of the YS HTT; the properties of XL and 2L HTT are inferred from those 2L, 3L and 3R HTT. See text for detailed explanation.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4481407&req=5

pgen.1005260.g012: Structure of Drosophila telomeres and subtelomeres.Schematic representation of Drosophila chromosome ends. From a distal to a proximal direction chromosome ends contain the terminin-associated region (red) that may extend for approximately 10 Kb (22), the HTT array that vary in length from 26 to 147 Kb [81] and may either repress (dark blue) or not repress (light blue) the expression of transgenes; the TAS sequences (light green) that comprise about 20 Kb [55, 81], or different types of chromatin: constitutive heterochromatin (Het, grey), or the 4th chromosome chromatin (4-ch, dark green) that has distinctive properties as well as properties shared by euchromatin and heterochromatin. The repressive properties of the YL, XR and 4L HTT have been inferred from those of the YS HTT; the properties of XL and 2L HTT are inferred from those 2L, 3L and 3R HTT. See text for detailed explanation.
Mentions: All Drosophila chromosomes of wild type strains terminate with HTT arrays of variable length (made of complete and incomplete HeT-A, TART and TAHRE elements) (reviewed in [5, 52, 53]) and are capped by the multiprotein terminin complex (reviewed in [6]). However Drosophila telomeres differ from each other in both the type of subtelomeric chromatin and in the properties of their HTT arrays (Fig 12). One of the most straightforward features that contradistinguish some of the Drosophila telomeres is their association with constitutive hetrochromatin. Approximately one-third of the Drosophila genome is made of constitutive heterochromatin; the entire Y chromosome, the short arm (XR) and the proximal 40% of the long arm (XL) of the X chromosome, the short arm (4L) and the proximal 70% of the long arm (4R) of the 4th chromosome, and the centric 25% of chromosomes 2 and 3 are heterochromatic [38, 54]. Thus the HTT arrays of YL, YS, XR and 4L are linked to constitutive heterochromatin (Fig 12). The HHT blocks of XL and those of the major autosomes are not directly associated with euchromatin but are instead juxtaposed to divergent clusters of subtelomeric repeats, known as telomere associated sequences (TAS) (reviewed in [55]). The TAS are not only different in sequence but are also occasionally absent from the subtelomeric regions, suggesting that their presence is not essential for proper telomere function [55]. Finally, the 4R telomere is joined to a special type of chromatin that has peculiar features, as well as features shared with both euchromatin and heterochromatin; for example the 4R distal chromatin is enriched in the 4th chromosome-specific Painting of four (Pof) protein and the heterochromatic markers HP1a and histone 3 methylated at lysine 9 (H3K9) (reviewed in [56]) (Fig 12).

Bottom Line: The Peo protein directly interacts with the terminin components, but peo mutations do not affect telomeric localization of HOAP, Moi, Ver and HP1a, suggesting that the peo-dependent telomere fusion phenotype is not due to loss of terminin from chromosome ends. peo mutants are also defective in DNA replication and PCNA recruitment.However, our results suggest that general defects in DNA replication are unable to induce TFs in Drosophila cells.We thus hypothesize that DNA replication in Peo-depleted cells results in specific fusigenic lesions concentrated in heterochromatin-associated telomeres.

View Article: PubMed Central - PubMed

Affiliation: Dipartimento di Biologia e Biotecnologie, Sapienza-Università di Roma, Roma, Italy; Istituto Pasteur Fondazione Cenci Bolognetti, Sapienza-Università di Roma, Roma, Italy.

ABSTRACT
Drosophila telomeres are sequence-independent structures that are maintained by transposition to chromosome ends of three specialized retroelements (HeT-A, TART and TAHRE; collectively designated as HTT) rather than telomerase activity. Fly telomeres are protected by the terminin complex (HOAP-HipHop-Moi-Ver) that localizes and functions exclusively at telomeres and by non-terminin proteins that do not serve telomere-specific functions. Although all Drosophila telomeres terminate with HTT arrays and are capped by terminin, they differ in the type of subtelomeric chromatin; the Y, XR, and 4L HTT are juxtaposed to constitutive heterochromatin, while the XL, 2L, 2R, 3L and 3R HTT are linked to the TAS repetitive sequences; the 4R HTT is associated with a chromatin that has features common to both euchromatin and heterochromatin. Here we show that mutations in pendolino (peo) cause telomeric fusions (TFs). The analysis of several peo mutant combinations showed that these TFs preferentially involve the Y, XR and 4th chromosome telomeres, a TF pattern never observed in the other 10 telomere-capping mutants so far characterized. peo encodes a non-terminin protein homologous to the E2 variant ubiquitin-conjugating enzymes. The Peo protein directly interacts with the terminin components, but peo mutations do not affect telomeric localization of HOAP, Moi, Ver and HP1a, suggesting that the peo-dependent telomere fusion phenotype is not due to loss of terminin from chromosome ends. peo mutants are also defective in DNA replication and PCNA recruitment. However, our results suggest that general defects in DNA replication are unable to induce TFs in Drosophila cells. We thus hypothesize that DNA replication in Peo-depleted cells results in specific fusigenic lesions concentrated in heterochromatin-associated telomeres. Alternatively, it is possible that Peo plays a dual function being independently required for DNA replication and telomere capping.

No MeSH data available.


Related in: MedlinePlus