Cytogenetic characterization and mapping of the repetitive DNAs in Cycloramphus bolitoglossus (Werner, 1897): More clues for the chromosome evolution in the genus Cycloramphus (Anura, Cycloramphidae)

Abstract

Cycloramphus bolitoglossus (Werner, 1897) is a rare species with a low population density in the Serra do Mar region of Paraná and Santa Catarina, in southern Brazil. Currently, it has been assigned to the Near Threatened (NT) category in the Brazilian List of Endangered Animal Species. Here, we described the karyotype of this species for the first time and investigated the patterns of some repetitive DNA classes in the chromosomes using molecular cytogenetic approaches. We isolated, sequenced and mapped the 5S rDNA and the satellite DNA PcP190 of C. bolitoglossus, as well as mapped the telomeric sequences and seven microsatellites motifies [(GA)15, (CA)15, (GACA)4, (GATA)8, (CAG)10, (CGC)10, and (GAA)]10. Cycloramphus bolitoglossus has 2n = 26 chromosomes and a fundamental number (FN) equal to 52, with a highly conserved karyotype compared to other genus members. Comparative cytogenetic under the phylogenetic context of genus allowed evolutionary interpretations of the morphological changes in the homologs of pairs 1, 3, and 6 along with the evolutionary history of Cycloramphus. Two subtypes of 5S rDNA type II were isolated in C. bolitoglossus genome, and several comparative analysis suggests mixed effects of concerted and birth-and-death evolution acting in this repetitive DNA. The 5S rDNA II subtype “a” and “b” was mapped on chromosome 1. However, their different position along chromosome 1 provide an excellent chromosome marker for future studies. PcP190 satellite DNA, already reported for species of the families Hylidae, Hylodidae, Leptodactylidae, and Odontophrynidae, is scattered throughout the C. bolitoglossus genome, and even non-heterochromatic regions showed hybridization signals using the PcP190 probe. Molecular analysis suggests that PcP190 satellite DNA exhibit a high-level of homogenization of this sequence in the genome of C. bolitoglossus. The PcP190 satDNA from C. bolitoglossus represents a novel sequence group, compared to other anurans, based on its hypervariable region. Overall, the present data on repetitive DNA sequences showed pseudogenization evidence and corroborated the hypothesis of the emergence of satDNA from rDNA 5S clusters. These two arguments that reinforced the importance of the birth-and-death evolutionary model to explain 5S rDNA patterns found in anuran genomes.

Comparative cytogenetics among Boana species (Anura, Hylidae): focus on evolutionary variability of repetitive DNA

“…Thus, the association of this heteromorphic region as polymorphic or associated with sex should be further investigated in B. albopunctata . However, this pattern of microsatellite organization in the euchromatin was also observed in the karyotypes of other vertebrates, non-related to the sex, as in Cheloniidae ( Machado et al, 2020 ) and Cycloramphidae species ( Bueno et al, 2021 ). Still, the absence of available genomic information does not allow us to understand the structure and functions of these regions.…”

In-Depth Satellitome Analyses of 37 Drosophila Species Illuminate Repetitive DNA Evolution in the Drosophila Genus

“…Despite their importance for genome organization, function, and evolution, SatDNA have been historically neglected in the Drosophila genomes and eukaryotes in general. SatDNA have been mainly utilized as taxonomic markers based on the number and morphology of signal-bearing chromosomes and on the localization of signals in different species ( Picariello et al 2002 ; Bueno et al 2021 ; Cabral-de-Mello et al 2021 ), but this approach usually requires a priori knowledge of its sequences. In Drosophila, SatDNA investigations began later than in other animals such as frogs and mice, starting with the use of CsCl density gradients to characterize the most abundant sequences in D. virilis , D. melanogaster , and D. hydei genomes ( Laird and McCarthy 1968 ; Gall et al 1971 ; Gall and Atherton 1974 ; Barnes et al 1978 ; Renkawitz 1979 ).…”

Comparative Distribution of Repetitive Sequences in the Karyotypes of Xenopus tropicalis and Xenopus laevis (Anura, Pipidae)

“…This includes the sex chromosomes, which are homomorphic in most amphibian species [10,11]. In this sense, repetitive DNA can be used as chromosomal Genes 2021, 12, 617 2 of 19 markers for comparative cytogenetic analysis [12,13] or for the identification of the sex chromosomes, as the accumulation of repetitive sequences is one of the first signs of sex chromosome differentiation according to the canonical pathway on the evolution of the sex chromosomes [14].…”