NOR and heterochromatin analysis in two cartilaginous fishes by C-, Ag- and RE (restriction endonuclease)-banding

Abstract

Selachian chromosomes were investigated for the first time by C-, Ag- and RE (restriction endonuclease)-band-ing. A pair of NOR-bearing acrocentric chromosomes, as well as a third extra site, were demonstrated in two species of Torpedo. In situ digestion with restriction endonucleases revealed a peculiar arrangement of constitutive heterochromatin: in Torpedo ocellata the centromere never appeared C-banded, and was always digested by AluI, PstI, DdeI and HaeIII; in Torpedo marmorata, instead, heterochromatin was present in the centromere, and was not digested by the same enzymes. The occurrence of different types of centromeric heterochromatin suggests an involvement of highly repeated DNA fractions in the Robertsonian phenomena that occurred in chromosome rearrangements in the genus Torpedo.

Molecular and Chromosomal Markers for Evolutionary Considerations in Torpediniformes (Chondrichthyes, Batoidea)

“…An interstitial and/or paracentromeric labeling on four bi-armed chromosomes was also evident (Figure 3). is interstitial FISH pattern might represent further evidence supporting the hypothesis that karyotype evolution in Torpediniformes occurred by a progressive reduction of chromosome number due to centric fusions [26,36]. In fact, species that underwent karyotype rearrangements as a result of Robertsonian fusions also show nontelomeric sites of the (TTAGGG) sequences in addition to the telomeric ones [37,38].…”

“…In this species, large amounts of highly repeated DNA [59], high heterogeneity in the genome composition [26], and a characteristic distribution of heterochromatin, that is never centromeric [36], have all been found.…”

“…FISH performed with the HpaI-like SINE probe on the T. torpedo chromosome revealed hybridization signals at the centromeric and/or the paracentromeric region on several biarmed chromosomes, while conspicuous �uorescent signals at the centromeric and/or telomeric level on the acrocentric ones were produced (Figure 4(a)), providing a hybridization pattern that is not coincident with that evidenced by C-banding [36]. Such a result is similar to that evidenced by Perez et al [43] on Atlantic salmon and rainbow trout karyotypes where the members of this SINE family are located only in the euchromatic regions of the chromosomes.…”

Sex-Related Genomic Sequences in Cartilaginous Fish: An Overview

“…The metaphasic plates were obtained according to the technique described by Stingo et al [1995], from spleen and gills of 3 coral catsharks (2 females and 1 male) from Singapore. The genomic DNA was isolated and amplified by PCR using the same primers as above [Rocco et al, 2009].…”

The chicken as a model to study microchromosomes in birds: a review

“…According to Rodionov [68], it might be tempting to consider them as ancestral chromosomes although they are very rare in fish and batracians. Indeed, they could have been inherited from a common ancestor of the vertebrates, as they can be encountered in primitive orders such as cartilaginous fish [59,75], salamanders [55] or monotreme [79]. Moreover [54].…”