Sex chromosome polymorphism and heterogametic males revealed by two cloned DNA probes in the ZW/ZZ fish Leporinus elongatus

Abstract

Abstract. In order to study the divergence of teleost sex chromosomes, subtractive cloning was carried out between genomic DNA ofmales and females ofthe rainbow trout (XX/XY) and of Leporinus elongatus (ZW /ZZ). Inserts cloned in a plasmid vector were individually tested on Southern blots of DNA of males and females for sex specificity. No sex-specific insert was obtained from trout, but two out of ten inserts cloned from L. elongatus showed sex-specific patterns in this species: one corresponds to a sequence present on both Z and W chromosomes, while the other is W specific. Sequences of these two inserts show neither clear homology with other known sequences, nor an open reading frame. They cross-hybridize with the genomic DNA of Leporinusfriderici, but without sex-specific patterns. Twenty-four L. elongatus adults were sexed by gonadal observation, chromosomed examination and Southern hybridization with one or the other insert. Ten males and 11 females had chromosomes and hybridization patterns typical of their sex. One ZW female was recognized as a male with the W-specific probe. This was also the case for two unusual ZW males, one having a male hybridization pattern with the other probe. These three atypical individuals may result from single genetic exchanges between four regions of the Z and the W, giving rise to three atypical W chromosomes. Finding males with such atypical heterochromosomes in a female heterogametic species may indicate that a gradual transition occurs between the heterogametic systems.

Sex chromosome composition revealed in Characidium fishes (Characiformes: Crenuchidae) by molecular cytogenetic methods

“…gomesi did not reveal any similarity among themselves or with any sequences deposited in GenBank to date (Table 3). This kind of dead-end result has been reported before when studying sequences present in the sex chromosomes of Leporinus elongatus (Nakayama et al 1994;Parisi-Maltempi et al 2007), Parodon hilarii Reinhardt, 1866 (Vicente et al 2003), Cydia pomonella L., 1758 (Fuková et al 2007) and Oryzias hubbsi Roberts, 1998 (Takehana et al 2012), for example. Of the seven distinct fragments analysed, only CgW9 evidenced similarity (∼73%) to a DNA transposon (Helitron-2 Dr) isolated from the genome of Danio rerio.…”

Particularities of reproduction and oogenesis in teleost fish compared to mammals

“…In fact, only some species exhibit morphologically differentiated sex chromosomes [6]. In the others, male or female heterogamety was first deduced from results of back crossing individuals obtained by hormonal sex reversion [7], like in tilapias Oreochromis mossambicus [8] and O. niloticus [9], or from artificial gynogenesis like in rainbow trout Oncorynchus mykiss [10].…”

Chromosome mapping of retrotransposable elementsRex1andRex3inLeporinusSpix, 1829 species (Characiformes: Anostomidae) and its relationships among heterochromatic segments and W sex chromosome

“…[26][27][28][29][30][31][32] In the present study, retrotransposable elements in the Rex family were also abundant in other heterochromatic regions in Leporinus chromosomes, such as terminal positions and some interstitial segments. This distribution reflects the pattern expected for transposable elements distribution described by Kidwell,7 related to a low rate of recombination.…”

“…25 Recent studies of Leporinus have isolated, characterized, and correlated repetitive elements in these species to study the evolution of sex chromosomes, as well as to discriminate hybrid species. [26][27][28][29][30][31][32] Other studies have shown that repetitive sequences such as 5S rDNA may have different distributions among Leporinus species with or without heteromorphic sex chromosomes. 33 The high heterochromatic content in the chromosomes of Leporinus species, especially the sex chromosomes, demonstrates the presence of high numbers of repetitive sequences in the genomes of these species.…”