Pair Of NORs Research Articles

Comparative study of four Mystus species (Bagridae, Siluriformes) from Thailand: insights into their karyotypic diversity

Karyotypes of four catfishes of the genus Mystus Scopoli, 1777 (family Bagridae), M. atrifasciatus Fowler, 1937, M. mysticetus Roberts, 1992, M. singaringan (Bleeker, 1846) and M. wolffii (Bleeker, 1851), were analysed by conventional and Ag-NOR banding as well as fluorescence in situ hybridization (FISH) techniques. Microsatellite d(GC)15, d(CAA)10, d(CAT)10 and d(GAA)10 repeat probes were applied in FISH. The obtained data revealed that the four studied species have different chromosome complements. The diploid chromosome numbers (2n) and the fundamental numbers (NF) range between 52 and 102, 54 and 104, 56 and 98, or 58 and 108 in M. mysticetus, M. atrifasciatus, M. singaringan or M. wolffii, respectively. Karyotype formulae of M. mysticetus, M. atrifasciatus, M. singaringan and M. wolffii are 24m+26sm+4a, 26m+24sm+2a, 24m+18sm+14a and 30m+22sm+6a, respectively. A single pair of NORs was identified adjacent to the telomeres of the short arm of chromosome pairs 3 (metacentric) in M. atrifasciatus, 20 (submetacentric) in M. mysticetus, 15 (submetacentric) in M. singaringan, and 5 (metacentric) in M. wolffii. The d(GC)15, d(CAA)10, d(CAT)10 and d(GAA)10 repeats were abundantly distributed in species-specific patterns. Overall, we present a comparison of cytogenetic and molecular cytogenetic patterns of four species from genus Mystus providing insights into their karyotype diversity in the genus.

Comparative study of four Mystus species (Bagridae, Siluriformes) from Thailand: insights into their karyotypic diversity.

Karyotypes of four catfishes of the genus Mystus Scopoli, 1777 (family Bagridae), M. atrifasciatus Fowler, 1937, M. mysticetus Roberts, 1992, M. singaringan (Bleeker, 1846) and M. wolffii (Bleeker, 1851), were analysed by conventional and Ag-NOR banding as well as fluorescence in situ hybridization (FISH) techniques. Microsatellite d(GC)15, d(CAA)10, d(CAT)10 and d(GAA)10 repeat probes were applied in FISH. The obtained data revealed that the four studied species have different chromosome complements. The diploid chromosome numbers (2n) and the fundamental numbers (NF) range between 52 and 102, 54 and 104, 56 and 98, or 58 and 108 in M. mysticetus, M. atrifasciatus, M. singaringan or M. wolffii, respectively. Karyotype formulae of M. mysticetus, M. atrifasciatus, M. singaringan and M. wolffii are 24m+26sm+4a, 26m+24sm+2a, 24m+18sm+14a and 30m+22sm+6a, respectively. A single pair of NORs was identified adjacent to the telomeres of the short arm of chromosome pairs 3 (metacentric) in M. atrifasciatus, 20 (submetacentric) in M. mysticetus, 15 (submetacentric) in M. singaringan, and 5 (metacentric) in M. wolffii. The d(GC)15, d(CAA)10, d(CAT)10 and d(GAA)10 repeats were abundantly distributed in species-specific patterns. Overall, we present a comparison of cytogenetic and molecular cytogenetic patterns of four species from genus Mystus providing insights into their karyotype diversity in the genus.

The First Karyological Analysis of the Sixbar Grouper Epinephelus sexfasciatus (Valenciennes, 1828) (Perciformes, Epinephelinae)

This study examines for the first time of karyotypic analysis and chromosomal characteristic of nucleolar organizer regions/NORs of Epinephelus sexfasciatus. The fish samples were collected from Andaman Sea, Phuket province, southern Thailand. The chromosomes were investigated using conventional Giemsa’s staining and Ag-NORs banding techniques. Fish chromosome preparations were conducted by squash technique from kidney. The results showed that the diploid chromosome number of E. sexfasciatus was 2n=48 and the fundamental number (NF, number of chromosome arms) was 48. The type of chromosomes included 24 large telocentric and 24 medium telocentric chromosomes. After Ag-NOR banding technique, single pair of NORs was observed on the short arm of medium telocentric chromosome pair 23. The idiogram shows gradually decreasing length of the chromosomes. A size difference of the largest and the smallest chromosomes is approximately two folds. The karyotype formula could be infered as: 2n(48) = 2n(48)= Lt24+Mt24.

Cytotaxonomic Studies in Four Species of Genus Puntius (Hamilton, 1822) from Central India

The cytotaxonomic analyses of four species of genus Puntius, viz. P. chola, P. conchonius, P. sophore and P. ticto from central India was carried out for the first time. The metaphase chromosomes were prepared from kidney and gill tissues. The diploid chromosome number and karyotype formula (KF) were found to be 50 & 2m + 4sm + 2st + 42t in P. chola; 50 & 14m + 28sm + 8st in P. conchonius; 48 & 4m + 2st + 42t in P. sophore and 50 & 14m + 24sm + 8st + 4t in P. ticto. Based on KF, the fundamental arm number were determined as 56, 92, 52 and 88, respectively, for these species. The karyomorphological features indicated that P. conchonius and P. ticto are closely related and the same holds true for P. chola and P. sophore. The chromosomes of all the four species exhibited constitutive heterochromatic blocks at their centromeric position, as detected by Cbanding technique. Variations in number of NORs were observed with presence of single pair of NORs in P. chola and P. conchonius, whereas in P. sophore and P. ticto multiple NORs were observed. Thus, based on the karyological features it can be hypothesized that P. conchonius and P. ticto may be in advanced stage of karyo-evolution.

A study on the karyotype, Ag-NORs and C-banding inEpinephelus bleekeri

Epinephelus bleekeri is important in commercial fisheries of tropical and subtropical seas.It has been broadly cultured in many Asian countries,such as China,Japan,Vietnam and Malaysia.Despite many studies on its culture techniques,the detailed cytogenetic data of this species is still lacking.To add E.bleekeri cytogenetic data and lay the foundation for grouper chromosome evolution and breeding studies,the karyotype of E.bleekeri was studied in this paper using multiple methods,including Giemsa staining,Ag-NORs and C-banding.The following results were obtained: E.bleekeri had a diploid chromosome number of 48 and its karyotype formula was 48t,NF=48,and sex chromosome was not observed;the con-stitutive heterochromatin was observed at the centromeric region on most chromosomes;but only a single pair of NORs was detected at the paracentromeric region of chromosome pair No.24.Based upon above results,it is concluded that E.bleekeri was relatively primitive among genus Epinephelus.

Botanical aspects of Heteropterys umbellata (Malpighiaceae): a cytological and palynological approach

The genus Heteropterys is one of the major genera in Malpighiaceae. However, few cytological and palynological studies were reported. The present work described for the first time the chromosome number, heterochromatin pattern, meiotic behavior, pollen viability and palynological aspects of Heteropterys ubellata, a very spread species. One large Brazilian population was evaluated using conventional techniques for meiotic studies and acetolyse to access the pollen morphology. The species showed 2n = 20 chromosomes, normal meiotic development and viable pollens. Great blocks of heterochromatin were observed around the centromers. DAPI staining was positive for centroeric heterochroatin, hile CMA3 ark as observed just at terinal regions of one pair of hoologues chromosomes. This result and the presence of one chromosome pair attached to the nucleoli during the pachytene and diakinesis suggested the presence of only one pair of NORs. Palynological analysis revealed that pollen grains are apolar, 6 porate and with colpoids associated to all pores. The pollen content was positive for the starch test, and the exine was rugulate with little psilate regions.

Nucleotide Sequences and Chromosomal Localization of 45S and 5S rDNA inNeolissochilus hexagonolepis(Pisces, Cyprinidae), Using Dual-Color Fish

Dual-color fluorescence in situ hybridization (FISH) was performed to study the simultaneous localization of major (45S) and minor (5S) family ribosomal RNA genes on chromosomes of Neolissochilus hexagonolepis. The partial 45S (18S, ITS 1, 5.8S, ITS 2 and 28S) and complete 5S (coding and NTS) rDNA units were amplified, sequenced, analyzed, and mapped on the metaphase chromosomes. The complete 18S, 5.8S and partial 28S rDNAs were 1849 bp, 157 bp and 1819 bp long, respectively. Internal transcribed spacers, namely ITS 1 (828 bp) and ITS 2 (359 bp), showed significant nucleotide variations from other fish species listed in NCBI database. The 5S rDNA contained an identical coding region of 120 bp and a highly divergent, non-transcribed 81-bp spacer. The specimens of N. hexagonolepis showed six bright fluorescent signals of 18S, while the 5S signals were present only on one pair of chromosomes. Subsequent analyses between conventional Ag-NORs and 18S rDNA FISH strongly suggested the possible inactivation of one pair of NORs that was localized at a telomeric position of a submetacentric chromosome. The sequencing and chromosomal localization of 45S and 5S rDNAs may serve as a useful genetic marker in taxonomic classification as well as in phylogenetic and evolutionary studies.

Karyological Characterization of Four Marine Fish Species, Genera Trachinotus and Selene (Perciformes: Carangidae), from the Southeast Brazilian Coast

Specimens of 4 marine fish species 3 from genus Trachinotus, T. carolinus, T. falcatus, T. goodei, and 1 from genus Selene, S. vomer belonging to the family Carangidae (Perciformes) were analyzed. All the specimens analyzed inhabit the South/Southeast coast of Brazil, and were sampled from the locality Sao Sebastiao, SP. The 4 species presented 2n=48 chromosomes, being the chromosome formula for Selene vomer 46A+2ST, T. carolinus 8MSM+40A, T. falcatus 38A+10MSM and T. goodei 4MSM+44A chromosomes. The 4 species presented 1 pair of NORs. Small blocks of heterochromatin were found in these 4 species. The karyotypic characteristics of these species were discussed in comparison with other species and populations of Perciformes already analysed.

NOR-Chromosome morphology and evidence for rDNA selection in phylactolaemates

Silver-stained chromosome spreads from the phylactolaemate ectoprocts Fredericella indica, Fredericella browni, Plumatella repens, Pectinatella magnifica and Asajirella gelatinosa show that each of these species has a single pair of NORs. In the first four species each NOR is immediately adjacent to the centromere of a large metacentric chromosome. Giemsa-stained preparations from Cristatella mucedo show centromeric gapping in a similar large metacentric, indicating the same type of NOR-chromosome. In Asajirella gelatinosa the two NORs are on a pair of smaller chromosomes, and are not immediately adjacent to a centromere. A close NOR-centromere association would inhibit meiotic crossing over in the NOR region. Since in phylactolaemates reproduction is primarily asexual, often by formation of statoblasts, there is potential intraclonal selection for favorable ribosomal DNA (rDNA) mutations, including from simultaneous germination of otherwise genetically identical statoblasts within a limited area and competition between cell lines within statoblasts. Inhibition of meiotic crossing over within the NOR would maintain its integrity during periods when intraclonal selection would not be occurring. This suggests that a more rapid rate of rDNA evolution is possible in phylactolaemates than in most other organisms, and is consistent with a derivation of this group from the morphologically similar phoronids, despite phylogenetic interpretations of rDNA sequence data that suggest the two groups are not closely related.

Chromosome study of swamp minnowEupallasella percnurus(Dybowski, 1916) from Poland

SUMMARYThe karyotype of swamp minnow, Eupallasella percnurus (= Phoxinus percnurus) from northern part of Poland was studied by conventional Giemsa staining and Ag-NOR technique. The diploid chromosome number 2n = 50, was composed of 5 pairs of metacentric, 15 pairs of submetacentric and 5 pairs of subtelo- to acrocentric chromosomes (NF = 90). Two pairs of NORs bearing chromosome were detected. They were located terminally on the short arms of one pair of medium sized submetacentric and on one pair of medium sized subtelocentric chromosomes. Most of the related species from the genus Phoxinus and Moroco had diploid chromosome number 2n = 50 and their karyotypes were also characterized by the biggest acrocentric pair. Most of the North American minnows species had one pair of NORs bearing chromosomes.

Karyotypes of Five Tetragonopterinae Species (Pisces, Characidae) from Argentina.

Karyotypic studies on five species (Characidae, Tetragonopterinae) from Argentina were carried out. Mitotic preparations from the kidney tissues were made by direct and short term culture methods. C-banding and silver staining was performed by conventional techniques. Astyanax bimaculatus, Gymnocorhimbus ternetzi and Moenkhausia sanctaefilomenae showed 2n = 50 chromosomes, with different karyotypic formulaes. Tetragonopterus argenteus showed 52 chromosomes and Astyanax schubarti 2n = 36 chromosomes. One pair of NORs was detected in most of species except in A. bimaculatus which showed numerical variation (1-6 carrier chromosomes) and size heteromorphism. The present paper reports the first cytogenetic study on the Tetragonopterinae from Argentina.

Cytogenetic analysis of gilthead seabream Sparus aurata (Pisces, Perciformes), a deletion affecting the NOR in a hatchery stock.

We have cytogenetically characterized a hatchery stock of gilthead seabream, Sparus aurata. The study included larvae, juveniles and adults. In S. aurata (diploid chromosome number 2n = 48), a pair of NORs is located at the ends of the short arms of the first submetacentric pair of chromosomes. In this stock we discovered a polymorphism which affects the NORs, and, by means of several cytogenetic and molecular techniques, we demonstrate that this polymorphism is due to the complete deletion of one of the two NORs in a high number of individuals. The significance of these cytogenetic characteristics for this species are discussed since they may be the source of aquaculture problems.

Structure and variation of the Nucleolus Organizer Region in turtles

Differential staining techniques were used to study the structure and variation of the NORs of 27 species of cryptodiran turtles. No species or individuals had more than a single pair of NORs. Extensive variation in NOR structure and chromosomal location was found among higher taxa and individual variation in NOR size was common. Thirty eight percent of all individuals studied were heterozygous for the size of the NOR. However, interspecific variation in chromosomal location and structure of the NOR within major taxa was relatively rare. It is concluded that ( I ) the pattern of variation of NORs is consistent with patterns of chromosomal evolution in turtles; (2) Turtles have only a single pair of NORs whereas other animals, such as some mammals, possess numerous NORs; (3) The heterochromatin associated with the NOR is involved in the structure of the nucleolus.