Sex Chromosome Differentiation in the Frog Genus Pseudis Involves Satellite DNA and Chromosome Rearrangements

Abstract

The genus Pseudis comprises six frogs of the family Hylidae and only P. tocantins had heteromorphic sex chromosomes detected by classical cytogenetics. In this species, the W chromosome is larger than the Z chromosome and has a large heterochromatic block located between the centromere and the nucleolus organizer region (NOR) in the long arm. This large heterochromatic band is enriched for the PcP190 satellite DNA (satDNA), whereas the Z chromosome bears a smaller C-band adjacent to the centromere in the long arm that is not detected by PcP190 probes. To assess sex chromosome differentiation in the genus Pseudis, we investigated the PcP190 satDNA in P. bolbodactyla, P. cardosoi, P. minuta, and P. paradoxa and in one species of Lysapsus, which is the sister genus of Pseudis. PcP190 sequences were isolated, sequenced, and the diversity of this class of satDNA was analyzed. To evaluate whether sex-related variations in PcP190 satDNA were present, we used in situ hybridization (for P. bolbodactyla, P. paradoxa, P. cardosoi, and P. minuta) and Southern blotting analysis (for all species). We found a low level of sex chromosome heteromorphism in P. bolbodactyla, as a PcP190 cluster was detected in the short arm of one of the homologs of pair 7 exclusively in females. In P. paradoxa, P. minuta, and P. cardosoi, PcP190 satDNA is not sex-related, although a cluster of PcP190 sequences could be recognized in the NOR-bearing chromosomes 7 of P. paradoxa and P. minuta and their homologous chromosome 5 of P. cardosoi. By tracking cytogenetic data in a species tree, we may hypothesize that the positioning of the PcP190 site adjacently to the NOR (as observed in the long arm of the W chromosome of P. tocantins) is a derived condition with respect to the location of the PcP190 site apart from the NOR, in the short arm of the NOR-bearing chromosomes 7 (as present in P. bolbodactyla, P. paradoxa, and P. minuta) or 5 (as present in P. cardosoi) and we discuss about the emergence of PcP190 satDNA as a sex-related trait.

Satellite DNA Mapping in Pseudis fusca (Hylidae, Pseudinae) Provides New Insights into Sex Chromosome Evolution in Paradoxical Frogs

“…Regarding NOR patterns, Pseudis sp. is similar to all other species of Pseudis with 2n = 24 [9], since in all of them the NOR is located in the long arm of chromosome 7 (which is the sex chromosome pair in P. tocantins [9] and P. bolbodactyla [11]). In P. cardosoi , the NOR-bearing chromosome is classified as chromosome 5, which is considered homeologous to chromosome 7 of the other species of Pseudis [48].…”

“…The PcP190 sequences obtained from Pseudis fusca are very similar to those classified previously as PcP-2 [10,11]. By sequencing PcP190 sequences from P. fusca , we increased the number of complete CR and HR sequences to 16 and 45, respectively, enabling a comparative analysis of similarity between CRs and HRs of a single type of PcP190 satDNA.…”

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)

“…All the monomers isolated in the same cloned sequence share an even higher mean level of similarity (95.54%). We recognized conserved (CR) and hypervariable (HR) regions, based on the classification of Gatto et al [ 25 ] ( Fig 5 ).…”

Extensive Cryptic Diversity Within the Physalaemus cuvieri–Physalaemus ephippifer Species Complex (Amphibia, Anura) Revealed by Cytogenetic, Mitochondrial, and Genomic Markers

“…After 4 h, they were euthanized with an overdose of 2% lidocaine (50 mg/g body weight—cutaneous administration) and had the intestines and testis removed. Chromosome preparations were obtained from these tissue samples following King and Rofe (1976), with modifications described in Gatto et al (2018), or following Schmid (1978). This protocol was approved by the Committee for Ethics in Animal Use of the University of Campinas (CEUA/UNICAMP) (permit number 3454-1).…”