Karyotype and cytogenetic mapping of 9 classes of repetitive DNAs in the genome of the naked catfish Mystus bocourti (Siluriformes, Bagridae)

Weerayuth Supiwong,Alongklod Tanomtong,Arunrat Chaveerach,Marcelo B Cioffi,Thomas Liehr,Krit Pinthong,Tawatchai Tanee,Nadezda Kosyakova

doi:10.1186/1755-8166-6-51

Abstract

BackgroundIn the present study, conventional and molecular cytogenetic studies were performed in the naked catfish Mystus bocourti (Siluriformes, Bagridae). Besides the conventional Giemsa staining, fluorescence in situ hybridization (FISH) using nine classes of repetitive DNAs namely 5S and 18S rDNAs, U2 snRNA, the microsatellites (CA)15 and (GA)15, telomeric repeats, and the retrotransposable elements Rex1, 3 and 6. was also performed.ResultsM. bocourti had 2n = 56 chromosomes with a karyotype composed by 11 m + 11 sm + 6 st/a and a fundamental number (NF) equal to 100 in both sexes. Heteromorphic sex chromosome cannot be identified. The U2 snRNA, 5S and 18S rDNA were present in only one pair of chromosomes but none of them in a syntenic position. Microsatellites (CA)15 and (GA)15 showed hybridization signals at subtelomeric regions of all chromosomes with a stronger accumulation into one specific chromosomal pair. FISH with the telomeric probe revealed hybridization signals on each telomere of all chromosomes and interstitial telomeric sites (ITS) were not detected. The retrotransposable elements Rex1, 3 and 6 were generally spread throughout the genome.ConclusionsIn general, the repetitive sequences were not randomly distributed in the genome, suggesting a pattern of compartmentalization on the heterochromatic region of the chromosomes. Little is known about the structure and organization of bagrid genomes and the knowledge of the chromosomal distribution of repetitive DNA sequences in M. bocourti represents the first step for achieving an integrated view of their genomes.

Highlights

In the present study, conventional and molecular cytogenetic studies were performed in the naked catfish Mystus bocourti (Siluriformes, Bagridae)
Physical mapping of repetitive sequences Simultaneous detection of 18S and 5S Ribosomal RNA (rRNA) by dualcolour fluorescence in situ hybridization (FISH) showed that both genes are located in the telomeric position of two distinct sm chromosomal pairs, not occupying a syntenic position
The same pattern was found for the U2 U2 spliceosomal small nuclear RNA (snRNA) gene, which was located in the short arm of one sm chromosomal pair (Figure 3)

Summary

Introduction

Conventional and molecular cytogenetic studies were performed in the naked catfish Mystus bocourti (Siluriformes, Bagridae). Besides the conventional Giemsa staining, fluorescence in situ hybridization (FISH) using nine classes of repetitive DNAs namely 5S and 18S rDNAs, U2 snRNA, the microsatellites (CA) and (GA), telomeric repeats, and the retrotransposable elements Rex and 6. Fishes of the Bagridae family belong to the order Siluriformes and are highly valued on the international fish market and represent promising species for aquaculture [1] They are distributed in both Africa and Asia, from Japan to Borneo, including Thailand. The species Mystus bocourti, commonly named as hi fin Mystus, is a medium-size bagrid, endemic to Chao Phraya and Mekong River basins [2] It can be distinguished from all other Mystus by its extraordinary high dorsal fin, involving great elongation of the non-serrate dorsal fin spine and first three or four soft rays [2] (Figure 1B). The molecular cytogenetic studies using fluorescence in situ hybridization (FISH) for mapping repetitive DNA sequences have provided important contributions to the characterization of the biodiversity and the evolution of several fish groups [6]

Methods

Results

Discussion

Conclusion