The key role of repeated DNAs in sex chromosome evolution in two fish species with ZW sex chromosome system

Abstract

Despite substantial progress, there are still several gaps in our knowledge about the process of sex chromosome differentiation. The degeneration of sex-specific chromosome in some species is well documented, but it is not clear if all species follow the same evolutionary pathway. The accumulation of repetitive DNA sequences, however, is a common feature. To better understand this involvement, fish species emerge as excellent models because they exhibit a wide variety of sex chromosome and sex determining systems. Besides, they have much younger sex chromosomes compared to higher vertebrates, making it possible to follow early steps of differentiation. Here, we analyzed the arrangement of 9 repetitive DNA sequences in the W chromosomes of 2 fish species, namely Leporinus reinhardti and Triportheus auritus, which present well-differentiated ZZ/ZW sex system, but differ in respect to the size of the sex-specific chromosome. Both W chromosomes are almost fully heterochromatic, with accumulation of repeated DNAs in their heterochromatic regions. We found that microsatellites have strongly accumulated on the large W chromosome of L. reinhardti but not on the reduced-size W chromosome of T. auritus and are therefore important players of the W chromosome expansion. The present data highlight that the evolution of the sex chromosomes can diverge even in the same type of sex system, with and without the degeneration of the specific-sex chromosome, being more dynamic than traditionally appreciated.

The Asian arowana (Scleropages formosus) genome provides new insights into the evolution of an early lineage of teleosts

“…However, in the current study, an elongated W chromosome was observed in the karyotype of arowana females. A similar phenomenon was reported earlier in other fish species and plants, including tongue sole 42 , Leporinus reinhardti 48 and papaya 49 . The apparent size increase of these W chromosomes could either be due to early accumulation of repeats that was shown to precede the transposon-driven decrease of size in heterogametic sex chromosomes 50 or to a higher proportion of insertion to deletions or to a recent translocation of an autosomal fragment onto the proto-W chromosome 47 .…”

Cytogenetic and Molecular Data Demonstrate that the Bryconinae (Ostariophysi, Bryconidae) Species from Southeastern Brazil Form a Phylogenetic and Phylogeographic Unit

“…To date, the cytogenetic data of Neotropical fishes have shown some major trends: karyotypic stability in Anostomidae [ 57 , 58 ], Prochilodontidae [ 58 , 59 – 61 ], and Curimatidae [ 57 , 62 ], and the existence of species complexes in the genera Astyanax [ 63 ] and Hoplias [ 64 ]. However, the cytogenetic pattern observed in bryconine from Brazilian southeastern coastal basins represents the first case in which synapomorphies of chromosomal banding show monophyly of well-defined morphological species.…”

Nuclear Integrants of Organellar DNA Contribute to Genome Structure and Evolution in Plants

“…The gathering of such novel sequences in sex chromosomes can promote recombination suppression of the sex chromosomes; when recombination is suppressed, such sequences can accumulate rapidly in the recombination-free region. The lack of recombination and release from purifying selection avoids their deletion from the recombination-suppressed region [87,88].…”