title: First insights on the retroelement Rex1 in the cytogenetics of frogs.
abstract: BACKGROUND
  While some transposable elements (TEs) have been found in the sequenced genomes of frog species, detailed studies of these elements have been lacking. In this work, we investigated the occurrence of the Rex1 element, which is widespread in fish, in anurans of the genus Physalaemus. We isolated and characterized the reverse transcriptase (RT)-coding sequences of Rex1 elements of five species of this genus.
  
  
  RESULTS
  The amino acid sequences deduced from the nucleotide sequences of the isolated fragments allowed us to unambiguously identify regions corresponding to domains 3-7 of RT. Some of the nucleotide sequences isolated from Physlaemus ephippifer and P. albonotatus had internal deletions, suggesting that these fragments are likely not active TEs, despite being derived from a Rex1 element. When hybridized with metaphase chromosomes, Rex1 probes were revealed at the pericentromeric heterochromatic region of the short arm of chromosome 3 of the P. ephippifer karyotype. Neither other heterochromatin sites of the P. ephippifer karyotype nor any chromosomal regions of the karyotypes of P. albonotatus, P. spiniger and P. albifrons were detected with these probes.
  
  
  CONCLUSIONS
  Rex1 elements were found in the genomes of five species of Physalaemus but clustered in only the P. ephippifer karyotype, in contrast to observations in some species of fish, where large chromosomal sites with Rex1 elements are typically present.
authors.affiliation: Departamento de Biologia Estrutural e Funcional, Instituto de Biologia, Universidade Estadual de Campinas, 13083-863 Campinas São Paulo, Brazil.
authors.forename: Juliana
authors.initials: J
authors.lastname: Nascimento
authors.affiliation: Laboratorio de Genética Evolutiva, Instituto de Biología Subtropical (CONICET-UNaM), Facultad de Ciencias Exactas Químicas y Naturales, Universidad Nacional de Misiones, Félix de Azara 1552, CPA N3300LQF Posadas, Misiones Argentina.
authors.forename: Diego
authors.initials: D
authors.lastname: Baldo
authors.affiliation: Departamento de Biologia Estrutural e Funcional, Instituto de Biologia, Universidade Estadual de Campinas, 13083-863 Campinas São Paulo, Brazil.
authors.forename: Luciana Bolsoni
authors.initials: LB
authors.lastname: Lourenço
keywords: Chromosome; Leptodactylidae; Repetitive DNA; Retrotransposon; in situ hybridization