Identification of two new repetitive elements and chromosomal mapping of repetitive DNA sequences in the fish Gymnothorax unicolor (Anguilliformes: Muraenidae)

Abstract

Muraenidae is a species-rich family, with relationships among genera and species and taxonomy that have not been completely clarified. Few cytogenetic studies have been conducted on this family, and all of them showed the same diploid chromosome number (2n=42) but with conspicuous karyotypic variation among species. The Mediterranean moray eel Gymnothorax unicolor was previously cytogenetically studied using classical techniques that allowed the characterization of its karyotype structure and the constitutive heterochromatin and argyrophilic nucleolar organizer regions (Ag-NORs) distribution pattern. In the present study, we describe two new repetitive elements (called GuMboI and GuDdeI) obtained from restricted genomic DNA of G. unicolor that were characterized by Southern blot and physically localized by in situ hybridization on metaphase chromosomes. As they are highly repetitive DNA sequences, they map in heterochromatic regions. However, while GuDdeI was localized in the centromeric regions, the GuMboI fraction was distributed on some centromeres and was co-localized with the nucleolus organizer region (NOR). Comparative analysis with other Mediterranean species such as Muraena helena pointed out that these DNA fractions are species-specific and could potentially be used for species discrimination. As a new contribution to the karyotype of this species, we found that the major ribosomal genes are localized on acrocentric chromosome 9 and that the telomeres of each chromosome are composed of a tandem repeat derived from a poly-TTAGGG DNA sequence, as it occurs in most vertebrate species. The results obtained add new information useful in comparative genomics at the chromosomal level and contribute to the cytogenetic knowledge regarding this fish family, which has not been extensively studied.

Comparative cytogenetics of six Indo‐Pacific moray eels (Anguilliformes: Muraenidae) by chromosomal banding and fluorescence in situ hybridization

“…The telomeric (TTAGGG) n sequence is highly conserved among vertebrates, including fishes. Among muraenids, this repeated sequence has been found to be restricted to the ends of all chromosomal arms, both in the species investigated in this study and in the previously studied species, M. helena, G. unicolor and G. tile (Salvadori et al, 1995;Coluccia et al, 2010Coluccia et al, , 2011. Rarely, the (TTAGGG) n sequence could be identified in an interstitial position (interstitial telomeric DNA sequences, ITSs).…”

“…unicolor and G . tile (Salvadori et al , ; Coluccia et al , , ). Rarely, the (TTAGGG) n sequence could be identified in an interstitial position (interstitial telomeric DNA sequences, ITSs).…”

“…The application of this technique for chromosome studies in muraenids, however, is still limited. To date, FISH has been employed for the localization of ribosomal, centromeric and telomeric DNA sequences of the Mediterranean moray Muraena helena L. 1758, the brown moray Gymnothorax unicolor (Delaroche 1809), and the freshwater moray Gymnothorax tile (Hamilton 1822) (Salvadori et al, 1995;Pichiri et al, 2000;Coluccia et al, 2010Coluccia et al, , 2011.…”

On the future contents of a small journal of histochemistry

“…118–124 Cytogenetic techniques have been used to identify repetitive DNA sequences in the genome of humans and other vertebrates. 121,125,126 …”

Triple-color FISH Karyotype Analysis of Four Korean Wild Cucurbitaceae Species

“…It is useful for elucidating genome structure and identifying chromosomes (Leitch and Heslop-Harrison, 1992;Kato et al, 2005;Abd El-Twab and Kondo, 2006). With the use of rDNAs and known cytogenetic markers, studies have traced chromosomal rearrangement during evolution and clarified phylogenetic relationships (Devi et al, 2005;Coluccia et al, 2011;Miao et al, 2016). FISH has facilitated chromosomal characterization in wild cucurbits, allowing wild species to be further exploited in breeding programs (Leitch and Heslop-Harrison, 1992;Anamthawat-Jónsson, 2001;Xu et al, 2007;Koo et al, 2010;Sousa et al, 2012;Miao et al, 2016).…”