title: Fragile sites, dysfunctional telomere and chromosome fusions: What is 5S rDNA role?
abstract: Repetitive DNA regions are known as fragile chromosomal sites which present a high flexibility and low stability. Our focus was characterize fragile sites in 5S rDNA regions. The Ancistrus sp. species shows a diploid number of 50 and an indicative Robertsonian fusion at chromosomal pair 1. Two sequences of 5S rDNA were identified: 5S.1 rDNA and 5S.2 rDNA. The first sequence gathers the necessary structures to gene expression and shows a functional secondary structure prediction. Otherwise, the 5S.2 rDNA sequence does not contain the upstream sequences that are required to expression, furthermore its structure prediction reveals a nonfunctional ribosomal RNA. The chromosomal mapping revealed several 5S.1 and 5S.2 rDNA clusters. In addition, the 5S.2 rDNA clusters were found in acrocentric and metacentric chromosomes proximal regions. The pair 1 5S.2 rDNA cluster is co-located with interstitial telomeric sites (ITS). Our results indicate that its clusters are hotspots to chromosomal breaks. During the meiotic prophase bouquet arrangement, double strand breaks (DSBs) at proximal 5S.2 rDNA of acrocentric chromosomes could lead to homologous and non-homologous repair mechanisms as Robertsonian fusions. Still, ITS sites provides chromosomal instability, resulting in telomeric recombination via TRF2 shelterin protein and a series of breakage-fusion-bridge cycles. Our proposal is that 5S rDNA derived sequences, act as chromosomal fragile sites in association with some chromosomal rearrangements of Loricariidae.
authors.affiliation: Department of Genetics, Federal University of Paraná, Curitiba, Paraná, Brazil.
authors.forename: Alain Victor
authors.initials: AV
authors.lastname: Barros
authors.affiliation: Department of Genetics, Federal University of Paraná, Curitiba, Paraná, Brazil.
authors.forename: Michele Andressa Vier
authors.initials: MA
authors.lastname: Wolski
authors.affiliation: Department of Structural Biology, Molecular and Genetics, State University of Ponta Grossa, Ponta Grossa, Paraná, Brazil.
authors.forename: Viviane
authors.initials: V
authors.lastname: Nogaroto
authors.affiliation: Department of Structural Biology, Molecular and Genetics, State University of Ponta Grossa, Ponta Grossa, Paraná, Brazil.
authors.forename: Mara Cristina
authors.initials: MC
authors.lastname: Almeida
authors.affiliation: Department of Genetics and Evolution, Federal University of São Carlos, São Carlos, São Paulo, Brazil.
authors.forename: Orlando
authors.initials: O
authors.lastname: Moreira-Filho
authors.affiliation: Department of Genetics, Federal University of Paraná, Curitiba, Paraná, Brazil; Department of Structural Biology, Molecular and Genetics, State University of Ponta Grossa, Ponta Grossa, Paraná, Brazil. Electronic address: vicarimr@pq.cnpq.br.
authors.forename: Marcelo Ricardo
authors.initials: MR
authors.lastname: Vicari
mesh_terms: D000818:Animals; D043171:Chromosomal Instability; D043283:Chromosome Fragile Sites; D004171:Diploidy; D019143:Evolution, Molecular; D050939:Gene Fusion / Q000235:genetics*; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D009690:Nucleic Acid Conformation; D012341:RNA, Ribosomal, 5S / Q000502:physiology*; D011995:Recombination, Genetic / Q000502:physiology*; D016615:Telomere / Q000235:genetics / Q000378:metabolism*
chemical_list: D012341:RNA, Ribosomal, 5S
keywords: 5S rRNA structure; FISH; Pseudogene; Robertsonian fusion; Telomeric instability