Early replication banding in Leporinus species (Osteichthyes, Characiformes) bearing differentiated sex chromosomes (ZW)

Abstract

There are few examples of differentiated sex chromosomes in fishes. In the genus Leporinus, seven species present a highly differentiated ZW system, derived from heterochromatinization process. Cytogenetic analyses carried out in three of these fish species, Leporinus obtusidens, L. elongatus and L. reinhardti, through RBG-banding, showed late replication bands, coincident with heterochromatic regions in both Z and W chromosomes. A similar interstitial early replication segment was observed in the complex heterochromatic region along the Wq arms in the three species, which might correspond to a pseudoautosomal segment (SD, sex determining locus). Asynchrony related to the replication pattern among different Z chromosomes was not observed. When the identification of nuclear organizer regions by silver nitrate was performed over chromosomal preparations previously exposed to 5-bromo-2'-deoxyuridine (BrdU), remarkable positive signals at interstitial and telomeric position were observed on the q arms of W chromosomes in the species L. elongatus and L. reinhardti. The absence of 18S ribosomal RNA gene loci in this region, formerly demonstrated by FISH, indicates that this argentophilic behavior is putatively due to heterochromatin decondensation caused by BrdU incorporation, favoring such Ag+ reaction. Early and late replication bands were also observed in the heterochromatic portions of Z and W chromosomes, indicating that euchromatic and heterochromatic regions are interspersed. The present data suggest a significant level of heterochromatic complexity in the sex chromosomes of each species. On the other hand, the replication pattern shared by them supports a monophyletic origin.

Physical mapping of 18S and 5S genes in pelagic species of the genera Caranx and Carangoides (Carangidae)

“…This condition, as well as reduced heterochromatin and localized pericentromeric positions, indicates conservation of chromosome structure (karyotypic stasis, sensu Molina and Galetti, 2007), which is widely disseminated within the Perciformes. The occurrence of reduced heterochromatization processes, such as those observed in Caranx and Carangoides, are thought to play a restrictive role in the karyotypic differentiation of species (Galetti et al, 2000;Galetti, 2004, 2007).…”

“…The carangids C. bartholomaei, C. latus, and C. lugubris, similarly to many other Perciformes species, have a karyotype of 48 chromosomes; this characteristic is considered to be basal and phylogenetically conserved within the order (Galetti et al, 2000;Molina and Galetti, 2007). In addition to conservation regarding the number of chromosomes, C. bartholomaei and C. latus share a similar karyotype (NF = 50).…”

Comparative cytogenetic analysis of marine needlefishes (Beloniformes) from southern Brazil

“…This diploid number is shared by approximately 60 % of marine Perciformes, and has been explained taking into account the occurrence of large populations and therefore intense gene flow due to extensive dispersion of eggs, larvae, or adults in the marine environment would thus reduce karyotype diversification (Molina and Galetti 2007).…”

Cytogenetic markers as diagnoses in the identification of the hybrid between Piauçu (Leporinus macrocephalus) and Piapara (Leporinus elongatus)

“…Besides the occurrence of normal homomorphic karyotypes in some Leporinus species, the occurrence of a ZZ/ZW sex chromosomes system was also observed (Galetti Jr. et al, 1981b;Foresti, 1986, 1987;Galetti Jr. et al, 1995;Molina and Galetti Jr., 2006). It involved a pair of large meta-and submetacentric chromosomes equivalent in size to the second pair, with the smaller metacentric chromosome corresponding to the Z and the submetacentric chromosome corresponding to the W chromosome (Galetti Jr. et al, 1981b;Galetti Jr. and Foresti, 1987).…”