Localization Of NORs Research Articles

Variability of NOR patterns in European water frogs of different genome composition and ploidy level.

We studied water frogs from a complex composed of two species: Pelophylax lessonae (Camerano, 1882) (genome LL, 2n = 26) and P. ridibundus (Pallas, 1771) (RR, 2 = 26), and their natural hybrid P. esculentus (Fitzinger, 1843) of various ploidy and genome composition (RL, 2n = 26, and RRL or RLL, 3n = 39). Tetraploids RRLL were found (4n = 52) in juveniles. We applied cytogenetic techniques: AgNO3, chromomycin A3, PI and fluorescent in situ hybridization with a 28S rDNA probe. Results obtained by silver staining corresponded well with those stained with CMA3, PI and FISH. As a rule, NORs are situated on chromosomes 10. The number of Ag-NORs visible on metaphase plates was the same as the number of Ag-nucleoli present in interphase nuclei of the same individual. In all analyzed metaphases, NORs exhibited variations in size after AgNO3 and CMA3 stainings. Sixty-six individuals (out of 407 analyzed) were polymorphic for the localization and number of NORs. Fifty-one diploids had NORs only on one chromosome of pair 10. Three triploids (LLR and RRL) displayed two NORs, and two other triploid RRL individuals displayed one, instead of expected three NORs. In ten individuals extra NORs were detected on chromosomes other than 10 (chromosomes 2 and 9).

Heterochromatin distribution and localization of NORs in the 2n = 48cytotypes of Nannospalax xanthodon and N. ehrenbergi

We compared the C-banding pattern and the NOR distribution in 3 populations of N. xanthodon and N. ehrenbergi with 48 chromosomes from Turkey, with the aim to reveal variations between and within species. We have found distinct variation in the C-banding and the NOR distribution pattern among the 3 populations compared; each of them possessed its own specific chromosomal features. However, it is not possible to distinguish between intra- and interspecific variation, and the observed patterns cannot be utilized for unequivocal species recognition.

New record on karyological analysis and first study of NOR localization of parthenogenetic brahminy blind snake, Ramphotyphlops braminus (Squamata, Typhlopidae) in Thailand

This is chromosomal analysis of the brahminy blind snake, Ramphotyphlops braminus (Daudin, 1803), a newly recorded species in northeastern Thailand. Mitotic chromosomes were prepared directly from intestinal epithelia cells of five brahminy blind snakes. Conventional staining and Ag-NOR banding techniques were applied to stain the chromosomes. The results showed that the triploid chromosome number was 3n = 42, while the fundamental number (NF) was 78. The types of chromosomes were 24 macrochromosomes (19 m + 5sm) and 18 microchromosomes (9 m + 3sm + 6 t). The region adjacent to the short arm near the telomere of one in macrochromosome pair 8 showed a clearly observable nucleolar organizer region/NOR. There were no irregularly sized chromosomes related to sex. The karyotype formula for R. braminus is as follows: 3n (42) = Lm 12 + Sm 7 + Ssm 5 + 18 microchromosomes.

First description of the karyotype and localization of major and minor ribosomal genes in Rhoadsiaaltipinna Fowler, 1911 (Characiformes, Characidae) from Ecuador.

Karyotypic features of Rhoadsia altipinna Fowler, 1911 from Ecuador were investigated by examining metaphase chromosomes through Giemsa staining, C-banding, Ag-NOR, and two-color-fluorescence in situ hybridization (FISH) for mapping of 18S and 5S ribosomal genes. The species exhibit a karyotype with 2n = 50, composed of 10 metacentric, 26 submetacentric and 14 subtelocentric elements, with a fundamental number FN=86 and is characterized by the presence of a larger metacentric pair (number 1), which is about 2/3 longer than the average length of the rest of the metacentric series. Sex chromosomes were not observed. Heterochromatin is identifiable on 44 chromosomes, distributed in paracentromeric position near the centromere. The first metacentric pair presents two well-defined heterochromatic blocks in paracentromeric position, near the centromere. Impregnation with silver nitrate showed a single pair of Ag-positive NORs localized at terminal regions of the short arms of the subtelocentric chromosome pair number 12. FISH assay confirmed these localization of NORs and revealed that minor rDNA clusters occur interstitially on the larger metacentric pair number 1. Comparison of results here reported with those available on other Characidae permit to hypothesize that the presence of a very large metacentric pair might represent a unique and derived condition that characterize one of four major lineages molecularly identified in this family.

The karyotype of the flathead sculpin Megalocottus platycephalus platycephalus (Pallas, 1814) (Pisces: Cottidae) from Odyan Bay, Sea of Okhotsk

This study deals with the karyotype of the flathead sculpin Megalocottus platycephalus platycephalus (Pallas, 1814) (family Cottidae) from Odyan Bay of the Sea of Okhotsk. The karyotype is stable: 2n = 42 (2 metacentric, 2 submeta-subtelocentric, 30 subtelocentric, and 8 acrocentric chromosomes), NF = 44 + 2. The nucleolar organizers (NOs) were identified using Ag-banding in the telomere parts of the short arms of two large subtelocentric chromosomes. Variations in the number of nucleolar organizer chromosomes and in the number of NO-staining blocks were found. Comparison of the karyotype of M. p. platycephalus with the karyotypes of previously studied species of the genus Myoxocephalus from the Sea of Japan and the Sea of Okhotsk revealed their significant similarity in the main features and difference in the number and localization of NORs.

Cytogenetic Analysis of Otiorhynchus bisulcatus (Fabricius, 1781) and O.(Zadrehus) atroapterus (De Geer, 1775) (Coleoptera, Curculionidae, Entiminae) using C Bands, NORs, and DAPI/CMA3 Staining

The structure of the karyotypes of two Otiorhynchus species belonging to separate subgenera, viz. Otiorhynchus s.str. bisulcatus and O. (Zadrehus) atroapterus, is compared and described for the first time. Both species have the same chromosome number (2n = 22), sex chromosome system of an achiasmate parachute type (Xy(p)), symmetric karyotype with the prevalence of metacentrics, similar meiotic behaviour, localization of NORs and positive DAPI signals. The main differences involve the morphology of autosomes and the X chromosome in the C-banding pattern and DAPI/CMA3 signals as well as in the presence of additional B chromosomes.

Localization of NORs in chromosomes of mouse cell lines by a combined 33258-Hoechst and Ag-staining technique.

Condensation of mouse C-heterochromatin is inhibited in cells of established mouse lines if treated with 33258 Hoechst. The fact that after such treatment these regions appear in mitotic chromosomes as longthreaded segments enabled us to localize, with the silver staining technique, the NORs outside the C-heterochromatin. The number of NORs per cell and their identification was determined.

Karyotypes and Chromosome Rearrangements in Two Tribes of Weevils (Coleoptera, Curculionidae: Sciaphilini and Brachydrini)

A description of karyotypes in two tribes of weevils, Sciaphilini and Brachyderini, was carried out with a discussion on the main trends of chromosomal evolution occurring in these groups. Some important cytological characteristics, such as chromosome morphology, sex determination type, pattern of male meiosis, B chromosome occurrence, as well as C-heterochromatin, NOR localization, and fluorochrome AT and GC specific staining are presented. The chromosome numbers and morphology in the two tribes of weevils are highly conserved. With the exception of one species, all possessed a diploid number of 22 chromosomes or triploid number of 33 chromosomes. Constitutive heterochromatin was observed in the pericentromeric regions of the majority ofthe chromosomes. In some species, additional constitutive heterochromatin was also observed in interstitial positions. The study of meiotic cells revealed the occurrence of total synapsis between autosomes, the presence of one terminal, interstitial or two chiasmata, reductional behaviour and regular segregation of all chromosomes, as well as the formation of associations of the Xy(p) type in sex chromosomes. Testicular cells impregnated with silver nitrate demonstrated NORs localized on autosomes and argentophilic material in the space between the X and y chromosomes. The use of CMA3/DAPI staining showed that centromeric heterochromatin is AT-rich, whereas CMA3 bands were probably conincident with NOR sites.

Cytogenetic characterization of alpaca (Lama pacos, fam. Camelidae) prometaphase chromosomes

The present study provides specific cytogenetic information on prometaphase chromosomes of the alpaca (Lama pacos, fam. Camelidae, 2n = 74) that forms a basis for future work on karyotype standardization and gene mapping of the species, as well as for comparative studies and future genetic improvement programs within the family Camelidae. Based on the centromeric index (CI) measurements, alpaca chromosomes have been classified into four groups: group A, subtelocentrics, from pair 1 to 10; group B, telocentrics, from pair 11 to 20; group C, submetacentrics, from pair 21 to 29; group D, metacentrics, from pair 30 to 36 plus sex chromosomes. For each chromosome pair, the following data are provided: relative chromosome length, centromeric index, conventional Giemsa staining, sequential QFQ/C-banding, GTG- and RBG-banding patterns with corresponding ideograms, RBA-banding and sequential RBA/silver staining for NOR localization. The overall number of RBG-bands revealed was 391. Nucleolus organizer-bearing chromosomes were identified as pairs 6, 28, 31, 32, 33 and 34. Comparative ZOO-FISH analysis with camel (Camelus dromedarius) X and Y painting probes was also carried out to validate X-Y chromosome identification of alpaca and to confirm close homologies between the sex chromosomes of these two species.

Cytogenetical and morphological features reveal significant differences among Venezuelan and Brazilian samples of Mugil curema (Teleostei: Mugilidae)

Karyotype of M. curema from the Gulf of Mexico and Brazil have been reported as possessing chromosome complement with 2n=28 and FN=48, whereas specimens from Venezuela has been reported as possessing a diploid number 2n=24 and a conserved FN (48). Although at first sight this variation suggests the presence of a chromosomal intraspecific (interpopulational) variability, the possibility that we are dealing with two different species was examined. This work revisit the karyotypes of M. curema from Venezuela and Brazil, including new data on C-banding, and NOR localization, and compares morphologic characteristics of samples from both localities. Thus, besides diploid number, the constitutive heterochromatin distribution and NORs location, mark other differences between M. curema Cytotype 1 (2n=28; FN=48) and Cytotype 2 (2n=24; NF=48). Moreover, morphologic comparison revealed differences in the scale counts and pectoral fin rays: 35 scales in the middle body line and 15 pectoral fin rays in specimens possessing the karyotype 2n=28, compared with 37-39 scales in the middle body line and 17 pectoral fin rays in specimens with the karyotype 2n=24. These differences lead us to suggest that both cytotypes are not related merely to geographic polytipic variations but could correspond to different species.

The karyology of ’Lacerta’ mosorensis Kolombatovic, 1886, and its bearing on phylogenetic relationships to other European Mountain lizards

The results are presented of a chromosomal study performed by means standard and banding staining methods in the Mosor rock lizard, ’Lacerta’ mosorensis, the last European mountain lizard to be karyotyped. It had a karyotype of 2n = 38 elements, 36 telocentric macrochromosomes + 2 microchromosomes, and NORs on peritelomeric regions of a medium‐small chromosome pair. C‐banding staining disclosed the presence of heteromorphic Z and W sex chromosomes. The W chromosome appeared to be completely heterochromatic and smaller than the Z one, which, instead, was mostly euchromatic. The results obtained show that ’L.’ mosorensis is karyologically unrelated to other European mountain lizards, whose karyotypes display a different chromosome number and/or localization of NORs.

Cytogenetics of two central Amazonian species of Colostethus (Anura, Dendrobatidae) with nidicolous tadpoles

A cytogenetic study of two central Amazonian species of Colostethus with nidicolous tadpoles indicated that Colostethus stepheni had 2n=24 chro- mosomes, whereas Colostethus nidicola had 2n=22 chromosomes. These species also differed in their NOR localization and C-banding pattern. These results sug- gest that karyotypic variation with a probable reduction in chromosome number and the presence of nidicolous tadpoles are independent events that may have occurred more than once during dendrobatid evolution.

Physical mapping of ribosomal DNA on several species of the subgenus Rosa

The localization of NORs by fluorescent in situ hybridization on metaphase spreads of five diploid (Rosa gigantea Coll., Rosa moschata Herrm., Rosa multiflora Thunb., Rosa rugosa Thunb. and Rosa sempervirens L., 2n=2x=14), one triploid (Rosa chinensis’semperflorens’ Koehne., 2n=3x=21) and one tetraploid (Rosa gallica ’versicolor’ L., 2n=4x=28) ancestral species of modern roses was studied. Two terminal hybridization signals were observed in all diploid species corresponding to a single NOR per genome in these species. Triploid R. chinensis showed three hybridization sites on the short arm of three morphologically similar chromosomes. Six hybridization sites, located at terminal positions of the short arms of three chromosome pairs, were observed in the tetraploid species. These signals corresponded to three pairs of NORs and all of them were located in chromosome pairs of different size. These observations, together with the analysis of meiotic pairing in PMCs, support the view that our specimen of R. chinensis is an autotriploid and that R. gallica’versicolor’ has an alloploidy nature.

Accentuated polymorphism of heterochromatin and nucleolar organizer regions in Astyanax scabripinnis (Pisces, Characidae): tools for understanding karyotypic evolution.

Astyanax scabripinnis has been considered a species complex because it presents high karyotypic and morphological variability among its populations. In this work, individuals of two A. scabripinnis populations from different streams in the same hydrographic basin were analyzed through C-banding and AgNOR. Although they present distinct diploid numbers, they show meta and submetacentric chromosome groups highly conserved (numerically and morphologically). Other chromosomal characteristics are also shared by both populations, as the pattern of constitutive heterochromatin distribution (large blocks in the telomeric regions of subtelocentric and acrocentric chromosomes) and some nucleolar chromosomes. Inter-individual variations both in the number and size of heterochromatic blocks, and in the number and localization of NORs were verified in the studied populations, characterizing them as polymorphics for these regions. The mechanisms involved in the dispersion of heterochromatin and NORs through the karyotypes, as well as the possible events related to the generation of polymorphism of those regions are discussed. Furthermore, relationships between these populations and within the context of the scabripinnis complex are also approached.

Cytogenetics of Edalorhina perezi(Anura, Leptodactylidae).

Specimens of Edalorhina perezi Jimenez de la Espada from the Brazilian Amazon were studied cytogenetically using Giemsa staining, silver staining and C-banding. The diploid complement of 2n=22 agreed with the chromosome number previously described for Edalorhina sp. Morphologically, the E. perezi karyotype resembled those of Physalaemus and Pleurodema species, but NOR localization and C-banding were unable to detect accurate homologies between E. perezi karyotype and those of the Physalaemus and Pleurodema species studied to date.

Nucleolar cycle and localization of NORs in early embryos of Parascaris univalens

Nucleolar cycle and localization of NORs in early embryos of Parascaris univalens

Chromosomal diversification in the gekkonid Tarentola mauritanica (Reptilia, Gekkonidae)

Abstract Chromosomes of various specimens belonging to four Italian and three African populations of Tarentola mauritanica were processed by Giemsa standard staining, by C‐, G‐, Ag‐NOR, DAPI‐banding methods and Alu I and Hae III endonuclease digestions. All specimens displayed a karyotype of 2n = 42 chromosomes, most of which were acrocentric and gradually decreasing in length. The karyotypes of the populations investigated proved different in the length of the short arms of acrocentric chromosomes, the number of dibrachial chromosomes and NOR localization. The presumptive chromosomal rearrangements are here indicated, and the implications of intraspecific diversification are discussed. Lastly, heterochromatin resistant to two common endonucleases may represent a relevant marker in the African Gekkoninae phylogenesis.

Karyotypes and Ag‐NORs of five Heteronemiidae (Insecta Phasmatodea) from Somalia

Abstract The karyotype and the NOR localization of five taxa of Heteronemiidae, belonging to the three genera known from Somalia are reported. The cytotaxonomy of stick insects in general and, in particular, of Heteronemiidae is rather poorly developed. The present paper aims to contribute to filling this gap. Diploid chromosome numbers are: Ramulus sansibarus, 44; R. lingulatus, R. affinis and Burria longixipha, 42; Palophus rothschildi, 32; the X chromosomes are the largest of the complement, and all taxa have an XX‐XO sex determination mechanism. In spite of the numerical similarity of the ramuline set, karyotypes differ markedly for chromosome constitution, their haploid N.F. ranging from 20 to 30, and for satellite/Ag‐NOR localizations. If R. libanicus (2n = 30, XX‐XY) is also considered, it can be seen that karyotype differences of taxa presently ascribed to the genus Ramulus are of the same magnitude as those of heterogenerically related species. The karyological features, together with morphologic...

Chromatid Separation Initiating from the NOR-bearing End of the Metaphase Chromosomes of Two Species of Aphis (Homoptera: Aphididae).

The localization of NORs in the somatic chromosomes of Aphis spiraecola Patch and A. craccivora Koch collected from the hosplants Solanum melongena and Dolichos lablab, respectively, was studied by the silver-staining method. In the interphase nuclei, frequently one or two, and rarely three silver-positive nucleoli appeared and continued to appear upto the early prophase. At metaphase, most of the plates revealed clearly the localization of NORs as tiny, round and deeply-stained dots at one terminal end of one pair of long chromosomes (pair no. 2) in the diploid complements (2n=8) of both the species. However, in a few slightly advanced metaphase plates in both the species, split NORs appearing as bifid structures were observed. The initiation of chromatid separation seemed to occur first from the NOR-bearing end in both the aphid species claimed to have holokinetic chromosomes.

Karyotyping and localization of nucleolar organizer regions in garlic, Allium sativum L.

The cytological features including chromosome counts and karyotypic features were investigated in a local cultivar of Allium sativum L. from Pakistan. Localization of NORs of chromosomes was also carried out. Actual lengths, relative lengths, short/long arm ratios of mitotic chromosomes were calculated from best five metaphase plates. Total relative length of chromosomes ranged from 7.5% to 5.0% and short/long arm ratios ranged from 1 and 0.5. Chromosomes 1 and 2 were median and the rest of the chromosomes was sub-median. N-banding was successfully used for identifying the bands at 4 NORs of chromosomes, whereas only two of them were darkly stained after silver nitrate staining.