title: Uncovering the Ancestry of B Chromosomes in Moenkhausia sanctaefilomenae (Teleostei, Characidae).
abstract: B chromosomes constitute a heterogeneous mixture of genomic parasites that are sometimes derived intraspecifically from the standard genome of the host species, but result from interspecific hybridization in other cases. The mode of origin determines the DNA content, with the B chromosomes showing high similarity with the A genome in the first case, but presenting higher similarity with a different species in the second. The characid fish Moenkhausia sanctaefilomenae harbours highly invasive B chromosomes, which are present in all populations analyzed to date in the Parana and Tietê rivers. To investigate the origin of these B chromosomes, we analyzed two natural populations: one carrying B chromosomes and the other lacking them, using a combination of molecular cytogenetic techniques, nucleotide sequence analysis and high-throughput sequencing (Illumina HiSeq2000). Our results showed that i) B chromosomes have not yet reached the Paranapanema River basin; ii) B chromosomes are mitotically unstable; iii) there are two types of B chromosomes, the most frequent of which is lightly C-banded (similar to euchromatin in A chromosomes) (B1), while the other is darkly C-banded (heterochromatin-like) (B2); iv) the two B types contain the same tandem repeat DNA sequences (18S ribosomal DNA, H3 histone genes, MS3 and MS7 satellite DNA), with a higher content of 18S rDNA in the heterochromatic variant; v) all of these repetitive DNAs are present together only in the paracentromeric region of autosome pair no. 6, suggesting that the B chromosomes are derived from this A chromosome; vi) the two B chromosome variants show MS3 sequences that are highly divergent from each other and from the 0B genome, although the B2-derived sequences exhibit higher similarity with the 0B genome (this suggests an independent origin of the two B variants, with the less frequent, B2 type presumably being younger); and vii) the dN/dS ratio for the H3.2 histone gene is almost 4-6 times higher for B chromosomes than for A chromosome sequences, suggesting that purifying selection is relaxed for the DNA sequences located on the B chromosomes, presumably because they are mostly inactive.
authors.affiliation: Departamento de Morfologia, Instituto de Biociências de Botucatu, Universidade Estadual Paulista, Botucatu, São Paulo, Brazil.
authors.forename: Ricardo
authors.initials: R
authors.lastname: Utsunomia
authors.affiliation: Departamento de Morfologia, Instituto de Biociências de Botucatu, Universidade Estadual Paulista, Botucatu, São Paulo, Brazil.
authors.forename: Duílio Mazzoni Zerbinato de Andrade
authors.initials: DM
authors.lastname: Silva
authors.affiliation: Departamento de Genética, Universidad de Granada, Granada, Spain.
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Ruiz-Ruano
authors.affiliation: Departamento de Morfologia, Instituto de Biociências de Botucatu, Universidade Estadual Paulista, Botucatu, São Paulo, Brazil.
authors.forename: Cristian
authors.initials: C
authors.lastname: Araya-Jaime
authors.affiliation: Departamento de Morfologia, Instituto de Biociências de Botucatu, Universidade Estadual Paulista, Botucatu, São Paulo, Brazil.
authors.forename: José Carlos
authors.initials: JC
authors.lastname: Pansonato-Alves
authors.affiliation: Departamento de Morfologia, Instituto de Biociências de Botucatu, Universidade Estadual Paulista, Botucatu, São Paulo, Brazil.
authors.forename: Priscilla Cardim
authors.initials: PC
authors.lastname: Scacchetti
authors.affiliation: CAUNESP, Universidade Estadual Paulista, Jaboticabal, São Paulo, Brazil.
authors.forename: Diogo Teruo
authors.initials: DT
authors.lastname: Hashimoto
authors.affiliation: Departamento de Morfologia, Instituto de Biociências de Botucatu, Universidade Estadual Paulista, Botucatu, São Paulo, Brazil.
authors.forename: Claudio
authors.initials: C
authors.lastname: Oliveira
authors.affiliation: Institute of Molecular and Cellular Biology SB RAS, Nobosibirsk, Russia.
authors.forename: Vladmir A
authors.initials: VA
authors.lastname: Trifonov
authors.affiliation: Departamento de Ciências Biológicas, Faculdade de Ciências, Universidade Estadual Paulista, Bauru, São Paulo, Brazil.
authors.forename: Fábio
authors.initials: F
authors.lastname: Porto-Foresti
authors.affiliation: Departamento de Genética, Universidad de Granada, Granada, Spain.
authors.forename: Juan Pedro M
authors.initials: JP
authors.lastname: Camacho
authors.affiliation: Departamento de Morfologia, Instituto de Biociências de Botucatu, Universidade Estadual Paulista, Botucatu, São Paulo, Brazil.
authors.forename: Fausto
authors.initials: F
authors.lastname: Foresti
mesh_terms: D000818:Animals; D060126:Characidae / Q000235:genetics* / Q000469:parasitology*; D043171:Chromosomal Instability; D002874:Chromosome Mapping; D002875:Chromosomes / Q000737:chemistry / Q000235:genetics* / Q000469:parasitology*; D004247:DNA / Q000032:analysis / Q000235:genetics; D005260:Female; D059785:Karyotype; D008297:Male; D008938:Mitosis
chemical_list: D004247:DNA