| Summary: | <p>Abstract</p> <p>Background</p> <p>For anurans, knowledge of 5S rDNA is scarce. For <it>Engystomops </it>species, chromosomal homeologies are difficult to recognize due to the high level of inter- and intraspecific cytogenetic variation. In an attempt to better compare the karyotypes of the Amazonian species <it>Engystomops freibergi </it>and <it>Engystomops petersi</it>, and to extend the knowledge of 5S rDNA organization in anurans, the 5S rDNA sequences of Amazonian <it>Engystomops </it>species were isolated, characterized, and mapped.</p> <p>Results</p> <p>Two types of 5S rDNA, which were readily differentiated by their NTS (non-transcribed spacer) sizes and compositions, were isolated from specimens of <it>E. freibergi </it>from Brazil and <it>E. petersi </it>from two Ecuadorian localities (Puyo and Yasuní). In the <it>E. freibergi </it>karyotypes, the entire type I 5S rDNA repeating unit hybridized to the pericentromeric region of 3p, whereas the entire type II 5S rDNA repeating unit mapped to the distal region of 6q, suggesting a differential localization of these sequences. The type I NTS probe clearly detected the 3p pericentromeric region in the karyotypes of <it>E. freibergi </it>and <it>E. petersi </it>from Puyo and the 5p pericentromeric region in the karyotype of <it>E. petersi </it>from Yasuní, but no distal or interstitial signals were observed. Interestingly, this probe also detected many centromeric regions in the three karyotypes, suggesting the presence of a satellite DNA family derived from 5S rDNA. The type II NTS probe detected only distal 6q regions in the three karyotypes, corroborating the differential distribution of the two types of 5S rDNA.</p> <p>Conclusions</p> <p>Because the 5S rDNA types found in <it>Engystomops </it>are related to those of <it>Physalaemus </it>with respect to their nucleotide sequences and chromosomal locations, their origin likely preceded the evolutionary divergence of these genera. In addition, our data indicated homeology between Chromosome 5 in <it>E. petersi </it>from Yasuní and Chromosomes 3 in <it>E. freibergi </it>and <it>E. petersi </it>from Puyo. In addition, the chromosomal location of the type II 5S rDNA corroborates the hypothesis that the Chromosomes 6 of <it>E. petersi </it>and <it>E. freibergi </it>are homeologous despite the great differences observed between the karyotypes of the Yasuní specimens and the others.</p>
|
|---|
