Alongklod Tanomtong

Genomic Organization of Repetitive DNA Elements and Its Implications for the Chromosomal Evolution of Channid Fishes (Actinopterygii, Perciformes)

Channid fishes, commonly referred to as “snakeheads”, are currently very important in Asian fishery and aquaculture due to the substantial decline in natural populations because of overexploitation. A large degree of chromosomal variation has been found in this family, mainly through the use of conventional cytogenetic investigations. In this study, we analyzed the karyotype structure and the distribution of 7 repetitive DNA sequences in several Channa species from different Thailand river basins. The aim of this study was to investigate the chromosomal differentiation among species and populations to improve upon the knowledge of its biodiversity and evolutionary history. Rearrangements, such as pericentric inversions, fusions and polyploidization, appear to be important events during the karyotypic evolution of this genus, resulting in the chromosomal diversity observed among the distinct species and even among populations of the same species. In addition, such variability is also increased by the genomic dynamism of repetitive elements, particularly by the differential distribution and accumulation of rDNA sequences on chromosomes. This marked diversity is likely linked to the lifestyle of the snakehead fishes and their population fragmentation, as already identified for other fish species. The karyotypic features highlight the biodiversity of the channid fishes and justify a taxonomic revision of the genus Channa, as well as of the Channidae family as a whole, as some nominal species may actually constitute species complexes.

Genomic organization of repetitive DNAs highlights chromosomal evolution in the genus Clarias (Clariidae, Siluriformes)

BackgroundThe genus Clarias (Clariidae, Siluriformes) contains at least 61 species naturally spread over vast regions of Asia, India and Africa. However, Clarias species have also been introduced in many different countries and represent the most widespread catfishes in the world. These fishes are also known as “walking catfishes” due to their ability to move over land. A large degree of chromosomal variation has been previously found in this family, mainly using conventional cytogenetic investigations, with diploid chromosome numbers ranging between 48 and 100. In this study, we analyzed the karyotype structure and distribution of four repetitive DNA sequences (5S and 18S rDNAs and (CA)15 and (GA)15 microsatellites) in three Clarias species (C. batrachus, C. gariepinus, C. macrocephalus), as well as in a probable natural hybrid of the two latter species from different Thailand river basins.ResultsClarias gariepinus and C. macrocephalus had 2n = 56 and 2n = 54, respectively, as well as karyotypes composed mainly by metacentric and submetacentric chromosomes. Their karyotypes differed in the number and location of 5S and 18S rDNA sites and in the degree of microsatellite accumulation. An intermediate chromosomal pattern incorporating those of the parental species was found in the probable hybrid, confirming its interspecific origin. Clarias batrachus had 2n = 104 chromosomes and its karyotype was dominated by mainly acrocentric elements, indicating that unusual multiple centric fissions were involved in its karyotype differentiation. The karyotype of this species presented an unexpected dispersion of ribosomal DNAs, possessing 54 and 12 sites of 5S and 18S rDNAs, respectively, as well as a high accumulation and differential distribution of both microsatellite repeats, representing ‘hot spots’ for chromosomal rearrangement.ConclusionBoth conventional and molecular cytogenetic markers were useful tools for demonstrating remarkable evolutionary dynamism and highlighting multiple chromosomal rearrangements and hybridization events correlated with the notable karyotypic diversity of these walking catfishes.

Karyotype homology between Calotes versicolor and C. mystaceus (Squamata, Agamidae) from northeastern Thailand

Karyotypes of Calotes versicolor and Calotes mystaceus from Khon Kaen Province, northeastern Thailand were investigated. Chromosome preparations were conducted by squash technique from bone marrow. Conventional Giemsa staining and Ag-NOR banding technique were applied to stain the chromosomes. The results showed that the diploid number of C. versicolor and C. mystaceus were 34 in both the species, while the fundamental number (NF) was 46 in both sexes of these species. The types of chromosomes were: four large metacentric, two large submetacentric, four medium metacentric, two small metacentric and 22 microchromosomes in the genus Calotes. NORs of these species were located at the secondary constriction to the telomere on the long arm of the large submetacentric chromosome pair no. 2. No difference was found in karyotypes of chromosomes prepared from the male and female agamid lizards used in the present study. The karyotype formulae of C. versicolor and C. mystaceus were found to be the same and were presented as 2n (34) = Lm4 + Lsm2 + Mm4 + Sm2 + 22 microchromosomes.

Cytogenetics of the skinks (Reptilia, Scincidae) from Thailand; IV: newly investigated karyotypic features of Lygosoma quadrupes and Scincella melanosticta

Abstract This study analyzed the karyotype of Lygosoma quadrupes and Scincella melanosticta from northeastern Thailand. Mitotic chromosomes were prepared directly from intestinal epithelial cells of three L. quadrupes and nine S. melanosticta. The chromosomes were stained by conventional staining technique. The karyotype was determined for each species based on at least 20 well-spread cells. Both L. quadrupes and S. melanosticta showed the same diploid number of 2n = 30, but differed in identical chromosome morphology. No sex chromosome heteromorphisms were evident in L. quadrupes; in contrast, S. melanosticta showed the ZZ/ZW sex determination system. The respective karyotype formulae of L. quadrupes and S. melanosticta were deduced as:

Cytogenetics of the skinks (Reptilia, Scincidae) from Thailand; III: the first karyological study of Sphenomorphus maculatus and Jarujinia bipedalis

Abstract This is a karyological study of male and female Sphenomorphus maculatus from Khon Kaen Province in Northeastern Thailand, and female Jarujinia bipedalis from Kanchanaburi Province in Central Thailand. Chromosomes of two species were prepared by the squash technique from the bone marrow and testis. Conventional staining and Ag-NOR banding techniques were applied to stain the chromosome with Giemsa’s solution and silver nitrate solution, respectively. The results showed that the diploid chromosome number of Sphenomorphus maculatus and Jarujinia bipedalis was 30 and the fundamental number (NF) was 44. There were eight large metacentric, two medium metacentric, four small metacentric and 16 microchromosomes in Sphenomorphus maculatus and eight large metacentric, six small metacentric, two small telocentric and 14 microchromosomes in Jarujinia bipedalis. There was no irregularly sized chromosome related to sex in either species. For Sphenomorphus maculatus, NORs are located at the telomere on the long arms of the second pair of the metacentric chromosome. The karyotype formulae were deduced as: 2n (30) = Lm8 + Mm2 + Sm4 + 16 microchromosomes and 2n (30) = Lm8 + Sm6 + St2 + 14 microchromosomes for Sphenomorphus maculatus and Jarujinia bipedalis, respectively.

Chromosomes in a genome-wise order: evidence for metaphase architecture

BackgroundOne fundamental finding of the last decade is that, besides the primary DNA sequence information there are several epigenetic “information-layers” like DNA-and histone modifications, chromatin packaging and, last but not least, the position of genes in the nucleus.ResultsWe postulate that the functional genomic architecture is not restricted to the interphase of the cell cycle but can also be observed in the metaphase stage, when chromosomes are most condensed and microscopically visible. If so, it offers the unique opportunity to directly analyze the functional aspects of genomic architecture in different cells, species and diseases. Another aspect not directly accessible by molecular techniques is the genome merged from two different haploid parental genomes represented by the homologous chromosome sets. Our results show that there is not only a well-known and defined nuclear architecture in interphase but also in metaphase leading to a bilateral organization of the two haploid sets of chromosomes. Moreover, evidence is provided for the parental origin of the haploid grouping.ConclusionsFrom our findings we postulate an additional epigenetic information layer within the genome including the organization of homologous chromosomes and their parental origin which may now substantially change the landscape of genetics.

Standardized karyotype of the three-spot gourami, Trichogaster trichopterus (Perciformes, Belontidae) from Thailand by conventional and Ag-NOR staining technique

Standardized karyotype and idiogram of the three-spot gourami (Trichogaster trichopterus) from local market in Roi-Et province, northeast Thailand, were studied. Kidney cell samples were taken from ten male and ten female fishes. The mitotic chromosome preparations were prepared by blood cell culture as well as directly from kidney cells. Conventional and Ag-NOR staining techniques were applied to stain the chromosomes. The results showed that diploid chromosome number of T. trichopterus was 2n = 46, the fundamental numbers (NF) were 46 in both male and female. The types of autosomes were 12 large telocentric, 32 medium telocentric and 2 small telocentric chromosomes. The region adjacent to the telomere of chromosome pair 2 showed clearly observable secondary constriction / NORs. The karyotype formula for T. trichopterus could be deduced as:

Chromosomes of Asian cyprinid fishes: cytogenetic analysis of two representatives of small paleotetraploid tribe Probarbini

{2}n\left( {\hbox{diploid}} \right){46} = {\hbox{L}}_{{12}}^{\rm{t}} + {\hbox{M}}_{{32}}^{\rm{t}} + {\hbox{S}}_2^{\rm{t}}