Abstract
The paradoxical frog Pseudis tocantins is the only species in the Hylidae family with known heteromorphic Z and W sex chromosomes. The Z chromosome is metacentric and presents an interstitial nucleolar organizer region (NOR) on the long arm that is adjacent to a pericentromeric heterochromatic band. In contrast, the submetacentric W chromosome carries a pericentromeric NOR on the long arm, which is adjacent to a clearly evident heterochromatic band that is larger than the band found on the Z chromosome and justify the size difference observed between these chromosomes. Here, we provide evidence that the non-centromeric heterochromatic bands in Zq and Wq differ not only in size and location but also in composition, based on comparative genomic hybridization (CGH) and an analysis of the anuran PcP190 satellite DNA. The finding of PcP190 sequences in P. tocantins extends the presence of this satellite DNA, which was previously detected among Leptodactylidae and Hylodidae, suggesting that this family of repetitive DNA is even older than it was formerly considered. Seven groups of PcP190 sequences were recognized in the genome of P. tocantins. PcP190 probes mapped to the heterochromatic band in Wq, and a Southern blot analysis indicated the accumulation of PcP190 in the female genome of P. tocantins, which suggests the involvement of this satellite DNA in the evolution of the sex chromosomes of this species.
Highlights
In vertebrates, sex determination may be triggered by genetic factors or environmental factors
PcP190 probes mapped to the heterochromatic band in Wq, and a Southern blot analysis indicated the accumulation of PcP190 in the female genome of P. tocantins, which suggests the involvement of this satellite DNA in the evolution of the sex chromosomes of this species
In the comparative genomic hybridization (CGH) experiments, a strong female-specific hybridization signal was observed at the heterochromatic block in the long arm of the W chromosome of Pseudis tocantins (Fig 1)
Summary
Sex determination may be triggered by genetic factors (genetic sex determination, GSD) or environmental factors (environment sex determination, ESD) (reviewed in [1] and [2]). Sex chromosomes are present in organisms with GSD, resulting in male heterogamety (as observed in mammals) or female heterogamety (common in birds and snakes). In amphibians, both male and female heterogamety are present (reviewed in [3] and [4]), but heteromorphic sex chromosomes may be recognized in only a few species [4, 5]. Approximately 40 species display heteromorphic sex chromosomes, which include cases of multiple sex chromosome systems (e.g., [6]) and 00/0W system [7], besides the usual XX/XY. The anurans are an interesting group for studying the evolution of sex chromosomes
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