The hnRNP A1 homolog Hrb87F/Hrp36 is important for telomere maintenance in Drosophila melanogaster
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Unlike the telomerase-dependent mammalian telomeres, HeT-A, TART, and TAHRE (HTT) retroposon arrays regulate Drosophila telomere length. Cap prevents telomeric associations (TAs) and telomeric fusions (TFs). Our results suggest important roles of Hrb87F in telomeric HTT array and cap maintenance in Drosophila. All chromosome arms, except 2L, in Df(3R)Hrb87F homozygotes (Hrb87F-null) displayed significantly elongated telomeres with amplified HTT arrays and high TAs, all of which resolved without damage. Presence of FLAG-tagged Hrb87F (FLAG-Hrb87F) on cap and subtelomeric regions following hsFLAG-Hrb87F transgene expression in Df(3R)Hrb87F homozygotes suppressed TAs without affecting telomere length. A normal X-chromosome telomere expanded within five generations in Hrb87F-null background and displayed high TAs, but not when hsFLAG-Hrb87F was co-expressed. Tel 1 /Gaiano line or HP1 loss-of-function mutant-derived expanded telomeres carry Hrb87F on cap and HTT arrays while Hrb87F-null telomeres have HP1 and HOAP on caps and expanded HTT arrays. ISWI, seen only on cap on normal telomeres, was abundant on Hrb87F-null expanded HTT arrays. Extended telomeres derived from Tel 1 (Gaiano) or HP1-null mutation background interact with those from Hrb87F-null, since while the end association frequency was negligible in Df(3R)Hrb87F/+ nuclei, it increased significantly in co-presence of Tel 1 or HP1-null-based expanded telomere/s. Together, these suggest complex interactions between members of the proteome of telomere so that absence of any key member leads to telomere expansion and/or enhanced TAs/TFs. HTT expansion in Hrb87F-null condition is not developmental but a germline event presumably because absence of Hrb87F in germline may deregulate HTT retroposition/replication leading to telomere elongation.
KeywordsHTT array HeT-A hnRNP Chromosome 4 Telomere association ISWI HP1 HOAP NonA Telomere fusion
We thank Dr. Mary-Lou Pardue for HeT-A clone (pBS 23Zn ORF) and critical suggestions; Dr. G. Cenci for Gaiano-I/Gaiano-I, Gaiano-III/Gaiano-III, and Su(var)205 05 /CyO; Dr. Susan Haynes for Df(3R)Hrb87F; Dr. Ann Beyer for hsFLAG-Hrb87F; and Bloomington Stock Centre for other fly stocks. We thank Dr. H. Saumweber (Berlin, Germany) for P11 and Bj6 antibodies, Dr. D. Corona (Palermo, Italy) for ISWI antibody, and Dr. Cenci and L. Ciapponi (Rome, Italy) for HOAP antibody. Financial support by the Department of Science & Technology, Govt. of India (New Delhi), through the Ramanna Fellowship and the National Facility for Confocal Microscopy grants and by the Board of Research in Nuclear Sciences (Department of Atomic Energy, Govt. of India) through Raja Ramanna Fellowship to SCL is acknowledged. AKS thanks the Council of Scientific & Industrial Research (New Delhi) for Senior Research Fellowship and the Department of Biotechnology, Govt. of India, for Research Associateship.
Compliance with ethical standards
This study was funded by
Department of Biotechnology, Ministry of Science and Technology, Govt. of India
Department of Atomic Energy, Govt. of India
Department of Science and Technology, Ministry of Science and Technology
Conflict of interest
AKS declares that he has no conflict of interest.
SCL declares that he has no conflict of interest.
All applicable international, national, and/or institutional guidelines for the care and use of animals were followed.
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