Location Of Nucleolus Organizer Regions Research Articles

Cytogenetic characterization of the greater amberjack, Seriola dumerili (Pisces: Carangidae), by different staining techniques and fluorescence in situ hybridization

A cytogenetic analysis by several staining techniques was carried out on specimens of Seriola dumerili from the Tyrrhenian coast of Sicily. The karyotype was found to be composed of 48 chromosomes in all the specimens examined. All chromosomes are subtelo- and acrocentrics, except for one pair of small-sized submetacentric chromosomes. After Ag-staining, nucleolus organizer regions (NORs) can be observed on the short arms of a medium-sized subtelocentric chromosome pair, and after chromomycin A3-staining a bright fluorescent signal is evident at the same sites. The 18S rDNA mapping by fluorescence in situ hybridization confirms this unique NOR location. The constitutive heterochromatin is mainly restricted to centromeres and the fluorochrome-staining by chromomycin A3 and 4′,6-diamidino-2-phenylindole revealed a uniform base composition along the chromosomal arms; therefore stock/population-specific marker chromosomes cannot be identified. Such cytogenetic features, however, rule out the presence of morphologically differentiated sex-chromosomes in the greater amberjack.

Chromosome-banding study of the Alaska blackfish, Dallia pectoralis (Euteleostei: Esocae), with implications for karyotype evolution and relationship of esocoid fishes

Chromosomes of Dallia pectoralis from two widely separated locations in Alaska (Yukon River system and Colville River) were analyzed by Giemsa staining, C-banding, and Chromomycin A3 fluorescence. The karyotype was redescribed more precisely. The diploid number 2n = 78 was found, but a significant number of cells with 74–77 chromosomes in individuals from the Yukon River indicate chromosomal polymorphism in the species. The diploid chromosome number of individuals from Colville River was constant (2n = 74). Colville River individuals had one more pair of metacentrics than Yukon River individuals with 2n = 76. The distribution of heterochromatin was nearly the same, and the number and location of nucleolar organizer regions (NORs) was identical. The variation (71–79) may be attributable to the association of NOR-bearing chromosomes or to chromosomal distinction between populations in the two rivers. The results suggest close relationships among all the species of Umbra, a closer relationship between Novumbra and Dallia than either bears to Umbra, and a possible closer relationship between Umbra and Esox than between Esox and Novumbra plus Dallia.

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

During early embryogenesis of the nematode Parascaris univalens (2n=2) the processes of chromatin diminution and segregation of the germ and somatic cell lineages take place simultaneously. In this study we analyzed the nucleolar cycle in early embryos, both in germinal and somatic blastomeres, by means of silver staining and antibodies against the nucleolar protein fibrillarin. We observed an identical nucleolar cycle in both types of blastomeres, hence, the chromatin diminution process has no effect on the nucleolar cycle of somatic blastomeres. We report the existence of outstanding differences between this cycle and those previously reported during early embryogenesis of other species. There is a true nucleolar cycle in early embryos that shows a peculiar nucleolar disorganization at prophase, and a preferential localization of prenucleolar bodies only on the euchromatic regions during nucleologenesis. Moreover, fibrillarin does not form a perichromosomal sheath in metaphase or anaphase holocentric chromosomes, probably owing to their special centromeric organization. The number and location of nucleolus organizer regions (NORs) in the chromosomal complement have been determined using silver impregnation, chromomycin A3/ distamycin A staining, and fluorescent in situ hybridization using an rDNA probe. There are only two NORs, one per chromosome, and these are located in the middle of the euchromatic central regions. This location implies that no rDNA sequences are lost in blastomeres after chromatin diminution. Moreover, the constant presence of two nucleoli in somatic blastomeres suggests that NORs are not affected during the fragmentation of euchromatic regions when this process occurs.

Cytogenetic Properties of Nine Species of Golden Moles (Insectivora: Chrysochloridae)

Standard karyotypes and the location of nucleolar organizer regions are reported for nine species of chrysochlorids representing five genera ( Amblysomus, Calcochloris, Chlorotalpa, Chrysochloris , and Chrysospalax ). Intraspecific karyotypic variation is negligible except in Amblysomus hottentotus , which displays three allopatric cytotypes characterized by differences in diploid number (30, 34, 36) and fundamental number (56, 60, 62, 68) as well as the number and location of nucleolar organizer regions. With the exception of Calcochloris , a monotypic genus with 2n = 28, most genera display 2n = 30, but differ in fundamental number and locations of nucleolar organizer regions. Evidence that the three cytotypes in A. hottentotus represent distinct biological species is presented. Cladisdc reladonships based on chromosomal properties support the recognition of Chlorotalpa and Calcochloris as discrete genera and the subgeneric recognition of the taxon Neamblysomus for the species A . ( N .) gunningi and A . ( N .) julianae . Limited banding studies indicate that centric fissions, tandem fusions, pericentric inversions, and heterochromatic additions may have played a role in the chromosomal evolution of chrysochlorids. Karyotypic evolution in the Chry-sochloridae appears to be similar in mode and tempo to that in other fossorial Insectivora, in contrast to subterranean rodents, which are characterized by greater chromosomal diversity and karyotypic orthoselection.

Cytogenetic peculiarities in the Algerian hedgehog: silver stains not only NORs but also heterochromatic blocks

Hedgehogs belong to one of the several mammalian taxa in which karyotype differences are based on variations in heterochromatin content. Furthermore, the number and location of nucleolar organizer regions (NORs) can also vary widely. In the present study these cytogenetic features were investigated in the Algerian hedgehog, Erinaceus (Aethechinus) algirus. The heterochromatin and NOR distribution patterns in the karyotype of this species are new among hedgehogs, whereas the euchromatic regions, including their G-band pattern, are similar to those reported by others. In addition, silver staining revealed a cytogenetic feature exclusive to the heterochromatic blocks of E. algirus: their silver staining with standard cytogenetic procedures. Because no similar phenomenon has been described previously in a mammalian species, several hypotheses about the significance and specificity of silver staining to NOR sites are discussed. Finally, the existence of different types of heterochromatin in the species analysed here, lead us to propose that what hedgehogs have inherited from their common ancestor is a mechanism which permits the accumulation of heterochromatin on specific chromosomes, rather than the heterochromatin itself.

A Monophyletic ZW Sex Chromosome System in Leporinus (Anostomidae, Characiformes).

Leporinus is a fish group rich in species which occurs from Central America to the River Plate basin in South America. From a cytologic viewpoint, this group is characterized by the occurrence of both homogametic and heterogametic species, a fact that renders it highly interesting for the study of sex chromosome evolution. In the present paper we report new occurrences of ZW sex chromosomes in L. trifasciatus from the Amazon region and L. conirostris from the basin of Eastern Brazil. Considerations about the origin and distribution of these sex chromosomes within the genus are also presented. The material was analyzed by standard Giemsa staining, by silver nitrate staining for the localization of nucleolar organizer regions, and by C banding for heterochromatin identification. The two species presented 2n=54 for both sexes as well as a large subtelocentric chromosome, the largest in the complement, exclusively detected in females, characterizing a W chromosome in both species. The heterochromatin data obtained permit us to assume that this system involves the same chromosomes not only in the species reported here but also in four others reported in previous studies. Thus the ZW system seems to have arisen only once in Leporinus and currently represent a unit of species more related to one another and cytologically distinct from the remaining species in the genus.

Chromosome polymorphism of Atlantic salmon (Salmo salar) from the River Dzwina, Baltic Sea Basin: arm length and NOR location variation of the eighth chromosome

A population of Atlantic salmon from the River Dzwina was karyotyped using conventional staining and banding techniques. The chromosome number was 2n = 58, and the chromosome arm number (NF) was 74. Variation in the size of the long arm of the eighth chromosome pair was observed. The presence of constitutive heterochromatin on this arm was confirmed by C-banding. Silver banding revealed variability in the location of nucleolus organizer regions (NORs) on this arm. Four cytotypes and three phenotypes of the NOR-bearing chromosome were found. The polymorphism of the eighth metacentric pair of chromosomes observed in Atlantic salmon was probably due to deletion and paracentric inversion of the arm involved.

Nucleolar chromosome variants inSternopygus macrurus(Pisces, Sternopygidae) from three Brazilian river basins

SUMMARYThe karyotypes, location of nucleolus organizer regions (NOR) and constitutive heterochromatin pattern of Sternopygus macrurus (Pisces, Gymnotoidei) of natural populations from the Amazon River, Sao Francisco River and Tiete River (the last belonging to the Upper Parana River system) are reported. All specimens had 2n = 46 chromosomes and presented small differences in karyotypic formulae, but populations of each river basin had a different fixed NOR phenotype. The loss of the satellite and a gradual deletion of the heterochromatin block adjacent to the NOR may be the origin of the variants. The possible mechanism of fixation of the NOR phenotypes, and the implications of the occurrence of intraspecific differences in fixed NOR phenotype in this species are discussed.

Phase specific Ag-staining of nucleolar organizer regions (NORs) and kinetochores in the Australian ant Myrmecia croslandi.

Detailed localization of NORs on metaphase chromosomes of the Australian ant Myrmecia croslandi were examined using rDNA: DNA in situ hybridization. In individuals with 2K=1M(1+2)+1SM 1+1M2 (2n=3) NORs are located at the proximal region of the short arm heterochromatin block in 1M(1+2), and at the chromosomal gap in the heterochromatic short arm of M2. These findings were supported by cytological evidence that nucleoli appeared exactly at the expected NOR sites. There was no silver staining at any of the metaphase NORs in this ant, but rather the kinetochores stained faintly.

Cytogenetics of bisexual/unisexual species of <i>Poecilia</i>

Chromosomes of the Amazon molly, Poecilia formosa, a unisexual species of hybrid origin, were investigated by C-banding, silver staining, and fluorescent staining with DAPI, quinacrine dihydrochloride, and chromomycin A3. Analysis of heterochromatin distribution indicates that chromosomes similar to the W chromosome of P. latipinna are not present in the unisexual species. Therefore, morphologically differentiated sex chromosomes do not form the basis of the unisexuality in P. formosa. The number and location of nucleolar organizer regions vary in P. formosa and do not correlate well with those of the parental species.

Identification of nucleolus organizer chromosomes in goat (Capra hircus)

SUMMARYSequential RBA/Ag-NOR- and GBG/Ag-NOR-banding techniques were employed on a total of fourteen Saanen and Maltese goats (Capra hircus, 2n = 60) reared in Southern Italy in order to identify which chromosomes carry nucleolus organizer regions (NORs). The procedure allowed the location of NORs at the telomeres of chromosomes 2, 3, 5, 6 and 28 of G-and R-banded goat karyotypes, which were arranged according to the ISCNDA (1989). The indirect comparison of goat, cattle and river buffalo nucleolar organizer (NO) chromosomes revealed the following common homologous NO-chromosomes: (a) 2, 3 and 6 between goat and cattle; (b) 6 (8) and 28 (4p) between goat and river buffalo; (c) 6 (8) among the three species.

Cytogenet Genome Res of bisexual/unisexual species of <i>Poecilia</i>

Three populations of the North American cyprinodont fish Poecilia latipinna, considered to be one of the progenitor species of the gynogenetic unisexual P. formosa, were analyzed by C-banding and Ag-staining. C-bands were found to be polymorphic, and Ag-staining showed a high degree of variability in both the number and location of nucleolus organizer regions. The C-banding and Ag-staining patterns allow, to a certain extent, to distinguish individual specimens from each of these populations. Females of the three populations were found to have a heteromorphic chromosome pair, which was frequently identifiable with Giemsa staining and always after C-banding. This pair could be interpreted as sex chromosomes of the ZW/ZZ type.

Chromosome Studies of European Leuciscine Fishes (Pisces Cyprinidae). Karyotype ofAspius Aspius

SUMMARYKaryotype of European leuciscine cyprinid species Aspius aspius from various river basins of Europe have been described. It consists of 7 pairs of metacentric, 14 pairs of submetacentric and 4 pairs of subtelocentric to acrocentric chromosomes including the «marker» leuciscine subtelocentric pair. According to its morphology, the karyotype is substantially the same as found in many other species of European leuciscine cyprinids. The only significant and remarkable difference is the localization of nucleolar organizer regions (NORs) as visualized by both silver staining and C-banding. Contrary to other species of European leuciscins, chromosomal NORs are located on the longer arms of the smallest pair of acrocentrics. This finding as well as the intraspecific karyotype variability of A. aspius has been discussed on the basis of our data as well as previous reports.

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.

Nucleolar organizer regions are associated with silver-stained chromatid cores in meiotic chromosomes of grasshoppers

Silver staining was employed to study the expression and localization of nucleolar organizer regions (NORs) and the localization and development of chromatid cores during the meiotic divisions of the grasshopper Chorthippus jucundus. NORs appear as silver-stained dots on the short arms of the L2 and L3 chromosomes and are always associated with chromatid cores. This observation provides an excellent chromosome marker to analyze the behaviour of chromatid cores during meiosis. Since both structures (NORs and chromatid cores) show a close interrelationship, we have obtained further evidence on the changes of organization that meiotic chromosomes undergo between metaphase I and anaphase I.Key words: nucleolar organizer region, meiosis, chromatid cores, chromosome structure, silver staining.

Chromosome Banding Studies in European Esocoid Fishes: Localization of Nucleolar Organizer Regions in Umbra krameri and Esox lucius

Chromosome Banding Studies in European Esocoid Fishes: Localization of Nucleolar Organizer Regions in Umbra krameri and Esox lucius

Differences in the location of nucleolus organizer regions in European vespertilionid bats

The karyotypes of European vespertilionid bats are distinguished by only a few, easily detectable differences in their G-banding patterns. Most rearrangements can be identified as Robertsonian translocations. Yet, there are surprising differences in the location of active nucleolus organizer regions (NORs), as revealed by silver staining. The ancestral position of the NOR is considered to be a secondary constriction on chromosome 15, as is the case in the genera Eptesicus, Nyctalus, and Vespertilio and in three of four Pipistrellus species. The remaining genera show multiple NOR sites located on minute short arms close to the centromere. In P. pipistrellus, differences in the location of the NORs correlate with the geographical origin of the animals. Some Myotis species possess NORs on numerous chromosomes and show great interindividual variability. In addition, two sibling species, M. brandtii and M. mystacinus, show completely different NOR locations.

Localization of NORs in the nucleolus-DNA body complex of the oocyte from the nemertine Amphiporus lactifloreus.

The nucleus of the premeiotic oocyte from the hoplonemertine Amphiporus lactifloreus contains a characteristic DNA-rich body that rapidly generates a peculiar nucleolar apparatus previously described as the nucleolus-DNA body complex. During early vitellogenesis, the nucleolar complex is centrally located in the nucleus and consists of many spherical and ribbon-shaped components-the nucleolar spherulae and lamellae-which produce hundreds of small peripheral nucleoli and several granular bodies as vitellogenesis progresses. Distributions of the nucleolar organizer regions (NORs) in various nucleolar components were studied by silver staining, and results were compared with previous findings obtained by cytochemical and autoradiographic techniques.The core of each spherula in the nucleolus-DNA body complex is strongly Ag-positive, and so, later on, is a minor part of each peripheral nucleolus. In contrast, the cortices of the nucleolar spherulae, in which slightly decondensed chromatin is distributed uniformly, and the nucleolar lamellae produced through self-peeling of the spherulae, do not react with silver. Thus, the NOR proteins identified by silver deposits correspond to numerous loci at which the most decondensed, transcriptionally active chromatin is made visible by the osmium-ammine reaction. These results are discussed in relation to the functional evolution of the initial DNA body of the oocyte from A. lactifloreus, the transcriptional abilities of its by-products, and the general process of the amplification of ribosomal genes.

Chromosome banding and phylogenetics of the golden mouse, Ochrotomys nuttalli

The number and location of nucleolus organizer regions, and G- and C-band karyotypes of Ochrotomys nuttalli were compared with those of other seemingly closely related New World peromyscine rodents. Although Ochrotomys was once considered a subgenus of Peromyscus, it shares few apparent G-band homologies with any peromyscine. The presumed homologous karyotypic elements shared between Ochrotomys and other peromyscine genera also are shared with Neotoma (the probable sister group of peromyscines) and these elements are hypothesized to be primitive for the group. The largest autosome in Ochrotomys appears to be shared with a distantly related species, Sigmodon hispidus, and this chromosome might be represented as two acrocentric autosomes (tandem fission products) in peromyscines and Neotoma. If this hypothesis is correct, the peromyscines as currently recognized likely are polyphyletic. The unusually extensive rearrangement of the Ochrotomys karyotype relative to peromyscines appears to represent a case of karyotypic megaevolution.

Conservation of nucleolus organizer regions during evolution in sheep, goat, cattle and aoudad.

There are ten nucleolus organizer regions (NORs) in domestic sheep (Ovis aries L.). cattle (Bos taurus L.), goat (Capra hircus L.) and aoudad (Ammotragus lervia Blyth) and these are located terminally on chromosomes with homologous (G-banding patterns. The similarity in number of nucleolus organizer regions in these species may indicate that their ribosomal DNA regions are infrequently involved in exchange events which could lead to different numbers of active nucleolus organizer regions. Other possible explanations of the conservation of number of nucleolus organizer regions in these species are discussed. The homology of NOR location in these species supports the idea that the Bovidae karyotype tends to be fairly stable apart from changes due to centric fusion events.