Active Nucleolar Organizer Regions Research Articles

Melatonin Level and Activity of Nucleolar Organizer Regions in the Prognosis of Infertility in Women with Ovarian Endometriosis

Introduction. Endometriosis is a multifactorial disease, affecting about 10 % of women of reproductive age. The purpose of the work is predicting the development of infertility in women with ovarian endometriosis by determining urine melatonin levels and activity indicators of nucleolar organizer regions in endometrioid ovarian heterotopias.Materials and methods. In the Clinic of South Ural State Medical University from 2018 to 2020, 2 groups of women with ovarian endometriosis were studied: group 1 — with infertility (n = 22); group 2 — without it (n = 27). The level of urinary 6-SMT and the activity of ribosomal synthesis were determined.Results. The level of 6-SMT is reduced in patients with stage I ovarian endometriosis. At stagesII and III, the level of 6-SMTis lower in women with infertility than without it: Stage II — (38.82±1.49) ng/ml and (93.04±3.64) ng/ml (p < 0.001); Stage III — (42.84±1.85) ng/ml and (58.06±1.65) ng/ml (p = 0.340). The activity of ribosomal synthesis in epithelial cells of endometrioid heterotopias increases at stage III. In fibroblasts of the stroma of endometrioid heterotopias, the activity of ribosomal synthesis is higherin women with stage III infertility, and in histiocytes— in women with stage II infertility. A logistic stepwise regression analysis was carried out and the most important predictors influencing the development of infertility were identified.Discussion. The decrease in melatonin in women with ovarian endometriosis, suffering from infertility, as well as in stage I ovarian endometriosis is consistent with the research of M. I. Yarmolinskaya et al. (2019). In the presence of infertility, activation of connective tissue histiocytes begins in the early stages. The results obtained may reflect the immunomodulatory effect of melatonin, which is expressed inincreased functional activity of connective tissue histiocytes and fibroblasts.Conclusion. Using mathematical analysis, the most important indicators that influence the reproductive prognosis in women with ovarian endometriosis (activity of nucleolar organizer regions, urine 6-SMT level) were determined, which makes it possible to create a model for calculating an individual reproductive prognosis.

Comparative analysis of karyotypes of Вovidae family from the evolutionary aspect

Aim. The aim of the study was to analyze chromosome sets of specific species of agricultural animals of Bovidae family using the techniques of differentiated G- and Ag-banding of chromosomes and to demonstrate the role of their variability in the evolution. Methods. The culture of lymphocytes and chromosome preparations were pre- pared by the method of Moorhead et al (1960). The preparations of metaphase chromosomes were analyzed by the G-banding methods of Barch M J et al (1997) and by Ag-banding method of Zhu JJ et al (2019). The chromosomal aberrations were classified according to the recommendations of the International System for Chromosome No- menclature of Domestic Bovids (2001). The dendrogram of phylogenetic relations between mammalian species was built using “STATISTICA 6.1”. Results. The comparative study of the chromosomal sets of cattle Bos taurus, domestic sheep Ovis aries and river buffalo Bubalus bubalis bubalis was conducted using G- and Ag-banding methods. The homology of the structural organization of chromosomes and the evolutionary changes in karyotypes of Bovidae family were analyzed, highlighting their sex chromosomes and the chromosomes with specific local- ized groups of gene linkage. A considerable homology of chromosome sites was found in the representatives of the investigated species by the G-banding profiles. To study the phylogenetic interrelations, the index of the number of active nucleolus organizer regions (NOR) in the chromosomes during the metaphase stage was used. Conclu- sions. The comparison of the morphology of chromosomes of agricultural animals of Bovidae family, Bos taurus, Ovis aries, and Bubalus bubalis bubalis confirms the association between the homology of some chromosomal sites and the formation of metacentric chromosomes due to the linkage of acrocentric ones. The species-specific morphological differences in sex chromosomes of the investigated animals were found in terms of the length and presence of pericentric inversions. The phylogenetic relations between the species of Bovidae family demonstrate that the value of distances, determined based on the variability of the number of active NOR, reflects the degree of their phylogenetic similarity.

Polymorphism of nucleolar organizer regions in different Ukrainian cattle breeds

Aim. To study the activity of nucleolar organizer regions (NORs) in different Ukrainian cattle breeds in terms of their apparent activity status in silver stain and possible relation with milk productivity. Methods. Chromosome prepara- tions using lymphocytes from the peripheral blood of 90 cows of different breeds were used in the study. NOR activity was determined by visual evaluation of concentrations of silver precipitation on NORs in individual chromosomes. A 50 % silver nitrate solution was used to stain chromosome preparations. NORs were detected as dark spots on telomeres of the corresponding chromosomes. Results. The cytological analysis of chromosome preparations from lymphocytes of first lactation cows detected NOR polymorphism in Ukrainian Red-and-Motley dairy cattle (URM), Ukrainian Black-and-White dairy breed (UBW), and hybrid cows, obtained by crossing Ukrainian Red-and-Motley dairy breed and Montbeliarde bulls (URM × M). First lactation cows of URM and UBM had higher or the same inci- dence of cells with four (29.8 and 30 %) and five (17.1 and 19.5 %) NORs, while in URM × M cows the incidence of cells with the same number of NORs was almost twice lower; cells with 7 and 8 NORs exceeded a similar index for other investigated breeds almost twice (2.5 against 4.5 % and 2.0 against 4.2 %). The highest level of chromosomal aberrations (CA) was observed in the group of animals with medium number (2 to 3 NORs per cell), and the lowest – in the group with a high number of NORs (from 6 to 7) with a reliable intergroup difference (p < 0.01). NOR activity was the highest in the group of animals of local origin (URM × M) with a milk yield over 7,000 kg in 305 days of the first lactation and the lowest in the UBW cows with a milk yield of 4–5,000 kg during the first lactation. Conclusions. We determined the differences in the activity of nucleolar organizers between the investigated groups of cows of dairy breed. URM × M hybrids reliably (р ≤ 0.05) exceeded dairy UBW cows by this index. No statistically significant different was found between other investigated groups of animals by this trait. Higher dairy productivity was found in the animals with higher frequency of NORs in the chromosomes of metaphase cells. In our opinion, the number of active NORs demonstrates relative variability between their number and the rate of protein synthesis, required to implement the productivity traits of the investigated animals.

Активность зон ядрышковых организаторов у женщин с эндометриозом яичников и бесплодием

Objective. To determine the activity of ribosomal synthesis and its connection with the level of melatonin in women with ovarian endometriosis and infertility. Patients and methods. The study included 49 women with ovarian endometriosis, who were divided into 2 groups: group 1 – 22 women with ovarian endometriosis and infertility, group 2 – 27 women with ovarian endometriosis without infertility. Medical history was collected from all women, who underwent therapeutic and diagnostic laparoscopy, the chronobiological type, the level of 6-sulfatoxymelatonin (aMT6s) in a first morning urine sample and the activity of nucleolar organizer regions in the foci of endometrioid heterotopias of the ovaries were determined. Results. It was found that the level of urinary 6-sulfatoxymelatonin was significantly reduced in patients with ovarian endometriosis and infertility compared to patients with endometriosis without infertility. In group 1, its level was 40.29 ± 7.25 ng/mL, in group 2 – 78.46 ± 15.46 ng/mL (p = 0.044). In patients with ovarian endometriosis and infertility, there was a moderate increase in the activity of ribosomal synthesis due to an increase in the number of intranucleolar inclusions against the background of decreased level of melatonin. In patients of group 2, with a decrease in the level of melatonin, ribosomal synthesis was activated by increasing the number of extranucleolar inclusions. This characterizes the high activity of ribosome synthesis in the cell. Conclusion. In women with ovarian endometriosis and infertility, against the background of low melatonin level, there was an increase in the activity of ribosomal synthesis in the cells of ovarian endometriotic formations. Key words: nucleolar organizer regions activity, melatonin, ovarian endometriosis

Double Robertsonian translocations in an infertile patient with macrocytic anemia: a case report

BackgroundConstitutional heterologous double Robertsonian translocations (DRT) between chromosomes 13/14 and chromosomes 14/15 with 44 chromosomes are extremely rare. In this case report, we present the karyotype analysis of metaphases prepared from bone marrow, peripheral blood and cultured skin tissue cells. These showed only 44 chromosomes with DRT involving chromosomes 13, 14 and 15. To our knowledge this is the first reported case with DRT involving chromosomes 14 and 15.Case presentationThe patient is an 81-year-old infertile male with a history of persistent macrocytic anemia (MA). The patient presented with fatigue, paleness of the skin, shortness of breath, lightheadedness and occasional dizziness. Work-up for common causes of macrocytic anemias in this case were excluded: folate/vitamin B12 deficiency, hypothyroidism, liver diseases, hemolysis, bleeding, alcoholism, exposure, HIV infection, chemotherapy or blood loss, drug-toxicity effect, or myelodysplasia. This individual with DRT had only six nucleolus organizer regions (NORs), instead of the usual ten, of which 50% of the 6 NORs were inactive (n = 3).ConclusionIn this case, macrocytic anemia (MA) appeared to be due to reduction in active NORs in DRT. We postulate that the marked reduction in active NORs leads to reduction in active nucleoli formation, which may be limiting ribosomal RNA synthesis, contributing to MA. It is probable that reduction in NOR activity affected normal DNA synthesis and cellular functions.

Comparative cytogenetics of the ground frogs Eupsophus emiliopugini Formas, 1989 and E. vertebralis Grandison, 1961 (Alsodidae) with comments on their inter- and intraspecific chromosome differentiation.

South American frogs of the genus Eupsophus Fitzinger, 1843 comprise 10 species. Two of them, Eupsophus vertebralis Grandison, 1961 and E. emiliopugini Formas, 1989 belong to the Eupsophus vertebralis group, exhibiting 2n = 28. Fundamental number differences between these species have been described using conventional chromosome staining of few specimens from only two localities. Here, classical techniques (Giemsa, C-banding, CMA3/DAPI banding, and Ag-NOR staining), and fluorescence in situ hybridization (FISH, with telomeric and 28S ribosomal probes), were applied on individuals of both species collected from 15 localities. We corroborate differences in fundamental numbers (FN) between E. vertebralis and E. emiliopugini through Giemsa staining and C-banding (FN = 54 and 56, respectively). No interstitial fluorescent signals, but clearly stained telomeric regions were detected by FISH using telomeric probe over spreads from both species. FISH with 28S rDNA probes and Ag-NOR staining confirmed the active nucleolus organizer regions signal on pair 5 for both species. Nevertheless, one E. emiliopugini individual from the Puyehue locality exhibited 28S ribosomal signals on pairs 4 and 5. Interestingly, only one chromosome of each pair showed Ag-NOR positive signals, showing a nucleolar dominance pattern. Chromosomal rearrangements, rRNA gene dosage control, mobile NORs elements, and/or species hybridization process could be involved in this interpopulation chromosomal variation.

Recurrent variation in the active NOR sites in the monkey frogs of the genus Pithecopus Cope, 1866 (Phyllomedusidae, Anura).

Treefrogs of the genus Pithecopus Cope, 1866 exhibit expressive chromosomal homogeneity which contrasts with a high variation frequency of the nucleolus organizer region (NOR) related to the group. Currently, the genus contains eleven species and no chromosomal data are available on P. palliatus Peters, 1873, P. ayeaye Lutz, 1966 and P. megacephalus Miranda-Ribeiro, 1926. Here, we describe the karyotypes of these three species based on Giemsa staining, C-banding, silver impregnation and in situ hybridization (FISH). We were also analyze the evolutionary dynamic of the NOR-bearing chromosome in species of genus under a phylogenetic view. The results indicate that P. palliatus, P. ayeaye, and P. megacephalus have similar karyotypes, which are typical of the genus Pithecopus. In P. palliatus the NOR was detected in the pericentromeric region of pair 9p whereas in P. ayeaye and P. megacephalus we report cases of the multiple NOR sites in karyotypes. In P. ayeaye the NOR was detected in the pericentromeric region of pair 9p in both homologues and additional sites was detected in pairs 3q, 4p, and 8q, all confirmed by FISH experiments. Already in P. megacephalus the NOR sites were detected in pericentromeric region homologues of pair 8q and additionally in one chromosome of pair 13q. A comparative overview of all the Pithecopus karyotypes analyzed up to now indicates the recurrence of the NOR-bearing chromosome pairs and the position of the NORs sites on these chromosomes. We hypothesized that this feature is a result of a polymorphic condition present in the common ancestor of Pithecopus. In such case, the lineages derived from polymorphic ancestor have reached fixation independently after divergence of lineages, resulting in a high level of homoplasy observed in this marker. Our findings help to fill the gaps in the understanding of the karyotype of the genus Pithecopus and reinforce the role of the evolutionary dynamics of the rDNA genes in karyotype diversification in this group.

Recurrent variation in the active NOR sites in the monkey frogs of the genus Pithecopus Cope, 1866 (Phyllomedusidae, Anura)

Treefrogs of the genus Pithecopus Cope, 1866 exhibit expressive chromosomal homogeneity which contrasts with a high variation frequency of the nucleolus organizer region (NOR) related to the group. Currently, the genus contains eleven species and no chromosomal data are available on P. palliatus Peters, 1873, P. ayeaye Lutz, 1966 and P. megacephalus Miranda-Ribeiro, 1926. Here, we describe the karyotypes of these three species based on Giemsa staining, C-banding, silver impregnation and in situ hybridization (FISH). We were also analyze the evolutionary dynamic of the NOR-bearing chromosome in species of genus under a phylogenetic view. The results indicate that P. palliatus, P. ayeaye, and P. megacephalus have similar karyotypes, which are typical of the genus Pithecopus. In P. palliatus the NOR was detected in the pericentromeric region of pair 9p whereas in P. ayeaye and P. megacephalus we report cases of the multiple NOR sites in karyotypes. In P. ayeaye the NOR was detected in the pericentromeric region of pair 9p in both homologues and additional sites was detected in pairs 3q, 4p, and 8q, all confirmed by FISH experiments. Already in P. megacephalus the NOR sites were detected in pericentromeric region homologues of pair 8q and additionally in one chromosome of pair 13q. A comparative overview of all the Pithecopus karyotypes analyzed up to now indicates the recurrence of the NOR-bearing chromosome pairs and the position of the NORs sites on these chromosomes. We hypothesized that this feature is a result of a polymorphic condition present in the common ancestor of Pithecopus. In such case, the lineages derived from polymorphic ancestor have reached fixation independently after divergence of lineages, resulting in a high level of homoplasy observed in this marker. Our findings help to fill the gaps in the understanding of the karyotype of the genus Pithecopus and reinforce the role of the evolutionary dynamics of the rDNA genes in karyotype diversification in this group.

Protein metabolic changes and nucleolus organizer regions activity in the lymphocytes of neonatal calves during the development of respiratory diseases.

Background and Aim:Calfhood disease is an important problem in dairy farming that could cause significant effects on heifer survival and productivity and has economic and welfare effects. Total protein concentration in the blood serum could be one of the predictors of bovine respiratory disease (BRD) in newborn calves. The number of active nucleolus organizers could be used to assess the viability of the protein synthesis system in cells and tissues. We aimed for a comparative assessment of the dynamics of the main indicators of protein metabolism and nucleolus organizer regions (NORs) activity in the lymphocytes of healthy calves (Group I) and calves with BRD (Group II) during the 1st month after birthMaterials and Methods:This study included 30 calves of the red-motley Holstein breed. Venous blood samples were taken from all calves on the 1st, 7th, 14th, and 28th days after birth. Quantitative analysis of total protein (Serum total protein [STP]), immune globulin (Serum immune globulin [SIg]), urea, and creatinine in serum and transcriptionally active chromosome NORs in the interphase nuclei of lymphocytes was conducted using receiver operating characteristic analysis and factor analysis.Results:In Group I, the STP levels decreased during the 1st month of life, and in Group II, the STP levels were variable. The STP levels in both groups remained within the reference intervals. During the first 2 weeks after birth, the calves’ SIg fluctuated within the statistical error limits and did not significantly differ between the groups. On the 28th day, SIg increased in both the groups (by 42.8% for Group I and 33.7% for Group II). The creatinine concentration showed a decrease but did not go beyond the range of reference values. Urea concentration in Group I markedly decreased and remained below the reference values; it did not change in Group II over the entire observation period. The number of NORs in 1-day-old calves did not significantly differ between the groups and amounted to 2.43 in Group I and 2.59 in Group II. A significant increase in the number of active NORs was found in calves in both groups at the ages of 14 and 28 days. Early BRD predictors (at 1-14 days) could not be identified among the studied indicators. The urea and creatinine concentrations and the NOR activity on day 28 after birth could be late BRD predictors. Protein metabolism in the newborn calves’ organisms is regulated by three types of factors: Maintenance of a constant protein concentration in the plasma, protein decomposition, and de novo synthesis.Conclusion:There were no observed significant differences in the protein metabolism values and dynamics of indicators between healthy calves and calves with developed BRD. Alterations in the studied characteristics are the result, but not the cause of BRD. The increase in active NORs under BRD could be a favorable forecasting indicator. Protection against foreign protein and genetic material is a more important task for the organism than ensuring growth processes during the neonatal period.

Karyotype structure and NOR activity in Brazilian Smilax Linnaeus, 1753 species (Smilacaceae).

The genus Smilax Linnaeus, 1753 (Smilacaceae) is a large genus of dioecious plants distributed in tropical, subtropical and temperate regions. Some Smilax species have medicinal importance and their identification is important for the control of raw material used in the manufacture of phytotherapeutical products. The karyotypes of seven Brazilian Smilax species were investigated. Mitotic metaphases of roots from young plants were analysed in Feulgen-stained preparations. The karyotypes were asymmetric and modal with 2n = 2x = 32 chromosomes gradually decreasing in size. In S. goyazana A De Candolle & C De Candolle, 1878, a polyploid species, 2n = 4x = 64. In all the species, the large and medium-sized chromosomes were subtelocentric and submetacentric and the small chromosomes were submetacentric or metacentric. Their karyotypes were quite similar, with differences in the arm ratio of some chromosomes. S. fluminensis Steudel, 1841 differed from the other species by having a large metacentric chromosome 1. These findings suggest that evolution occurred without drastic changes in the chromosomal structure in the species analyzed. Terminal secondary constrictions were visualized on the short arm of some chromosomes, but they were detected only in one homologue of each pair. Due to the terminal location and the degree of chromosome condensation, secondary constrictions were not visualized in some species. The nucleolus organizer regions (NORs) were mapped by silver-staining and fluorescent in situ hybridization (FISH) in S. rufescens Grisebach, 1842 and S. fluminensis. Silver-staining and FISH signals were colocalized on the short arms of six chromosomes in S. rufescens and four chromosomes in S. fluminensis. In FISH preparations, one of the largest chromosomes had the secondary constrictions highly decondensed in some cells. This finding and the heteromorphism observed in Feulgen-stained chromosomes suggest that differential rRNA gene expression between homologous rDNA loci can occur in some cells, resulting in different degrees of ribosomal chromatin decondensation. The presence of a heteromorphic chromosome pair in S. rufescens, S. polyantha Grisebach, 1842 and S. goyazana suggests a chromosomal sex determination in these dioecious species.

Cytogenetic instability of chromosomal nucleolar organizer regions (NORs) in cloned mouse L929 fibroblasts.

Ribosomal DNA (rDNA) gene codes for 18S, 5.8S, and 28S rRNA form tandem repetitive clusters, which occupy distinct chromosomal loci called nucleolar organizer regions (NORs). The number and position of NORs on chromosomes are genetic characteristics of the species although within a cell, the NOR sizes can significantly vary due to loss or multiplication of rDNA copies. In the current study, we used mouse L929 fibroblasts, the aneuploid cells which differ in the FISH- and Ag-NOR numbers, to examine whether the parental NOR variability is inherited in clones. By statistical analysis, we showed that the cloned fibroblasts were able to restore the NOR numerical characteristics of the parental cells after long-term culturing. These results support the idea that mammalian cells may have mechanisms which control the number and activity of NORs at the population level. In L929 fibroblasts, we also regularly observed laterally asymmetry of FISH-NORs that evidenced in an unequal distribution of the mother rDNA copies between the daughter cells in mitosis.

“Space” Pea Pisum sativum L. and Wheat Triticum compactum Host. Plants as Objects of Cytogenetic Studies

The peculiarities of meiosis, C-heterochromatin (C-HC) distribution, and the activity of nucleolus organizer regions (NORs) of the chromosomes were studied in the Pisum sativum L. pea and Triticum compactum Host. club wheat grown from the seeds obtained in Lada space greenhouse on the board of RS ISS. It was noted that the analysis of meiosis detected no significant violations in the “space” plant cells, and the total amount of C-HC did not differ significantly from the control, despite the polymorphism of the chromosome C-banding pattern. Paracentric inversion on the chromosome 4A was found for the first time in the T. compactum, while no additional active NOR chromosomes were found.

Evolution of trans-Andean endemic fishes of the genus Cheirodon (Teleostei: Characidae) are associated with chromosomal rearrangements

BackgroundAmong Neotropical fishes, the family Characidae is highly diverse and speciose and its taxonomy is not completely resolved. In Chile, the family is represented by five species, all within the genus Cheirodon, of which C. pisciculus, C. galusdae, C. kiliani, and C. australe are endemic, while C. interruptus is introduced. We compared chromosomal markers in order to appreciate the taxonomy and evolution of these trans-Andean fishes.ResultsThe specimens were photographed in stereomicroscope to observe the ventral protrusive teeth and cusps for morphological analysis and species identification. All of the species analysed had equally diploid chromosome number 2n = 50, with karyotypes dominated by high number of acrocentric chromosomes as compared to those of other members of Cheirodontinae. The distribution of heterochromatin was inconspicuous and was similar in all the species. The number of active NORs (nucleolus organizer regions) was polymorphic, with the greater number of them in C. kiliani and C. galusdae. The location of 5S and 18S rDNA ranged in number and position, showing two sites in different chromosomes. The fluorescent in situ hybridization with telomeric probe did not reveal interstitial sites in all analysed species.ConclusionsThe comparative analysis of karyotypes and morphological markers revealed a biogeographic pattern of distribution, with the species that occur in the southern region forming one group and those in central and northern Chile forming another.

The Case of X and Y Localization of Nucleolus Organizer Regions (NORs) in Tragulus javanicus (Cetartiodactyla, Mammalia).

There are differences in number and localization of nucleolus organizer regions (NORs) in genomes. In mammalian genomes, NORs are located on autosomes, which are often situated on short arms of acrocentric chromosomes and more rarely in telomeric, pericentromeric, or interstitial regions. In this work, we report the unique case of active NORs located on gonоsomes of a eutherian mammal, the Javan mouse-deer (Tragulus javanicus). We have investigated the position of NORs by FISH experiments with ribosomal DNA (rDNA) sequences (18S, 5.8S, and 28S) and show the presence of a single NOR site on the X and Y chromosomes. The NOR is localized interstitially on the p-arm of the X chromosome in close proximity with prominent C-positive heterochromatin blocks and in the pericentromeric area of mostly heterochromatic Y. The NOR sites are active on both the X and Y chromosomes in the studied individual and surrounded by GC enriched heterochromatin. We hypothesize that the surrounding heterochromatin might have played a role in the transfer of NORs from autosomes to sex chromosomes during the karyotype evolution of the Javan mouse-deer.

Identification of a New Mullet Species Complex Based on an Integrative Molecular and Cytogenetic Investigation of Mugil hospes (Mugilidae: Mugiliformes).

Mullets are very common fishes included in the family Mugilidae, (Mugiliformes), which are characterized by both a remarkably uniform external morphology and internal anatomy. Recently, within this family, different species complexes were molecularly identified within Mugil, a genus which is characterized by lineages that sometimes show very different karyotypes. Here we report the results of cytogenetic and molecular analyses conducted on Mugil hospes, commonly known as the hospe mullet, from Ecuador. The study aims to verify whether the original described species from the Pacific Ocean corresponds to that identified in the Atlantic Ocean, and to identify species-specific chromosome markers that can add new comparative data about Mugilidae karyotype evolution. The karyotype of M. hospes from Ecuador is composed of 48 acrocentric chromosomes and shows two active nucleolar organizer regions (NORs). In situ hybridization, using different types of repetitive sequences (rDNAs, U1 snDNA, telomeric repeats) as probes, identified species-specific chromosome markers that have been compared with those of other species of the genus Mugil. Cytochrome c oxidase subunit I (COI) sequence analysis shows only 92–93% similarity with sequences previously deposited under this species name in GenBank, all of which were from the Atlantic Ocean. Phylogenetic reconstructions indicate the presence of three well-supported hospe mullet lineages whose molecular divergence is compatible with the presence of distinct species. Indeed, the first lineage includes samples from Ecuador, whereas the other two lineages include the Atlantic samples and correspond to M. brevirostris from Brazil and Mugil sp. R from Belize/Venezuela. Results here provided reiterate the pivotal importance of an integrative molecular and cytogenetic approach in the reconstruction of the relationships within Mugilidae.

C- and NOR-banding karyotype analysis of Nannospalax xanthodon (2n = 52, 2n = 60) and new locality for 2n = 52 cytotype from western Anatolia

This study investigated C-heterochromatin and NOR (nucleolar organizer region) characteristics of 2n = 52 and 2n = 60 chromosomal forms of Nannospalax xanthodon (blind mole rat), which are separated by the Sakarya River in Bilecik Province. In addition, a new locality was included to the geographical border of 2n = 52 NF = 70 cytotypes. According to the results of C-banding, centromeric heterochromatin was detected in three pairs of chromosomes and telomeric heterochromatin was detected in three pairs of chromosomes in the 2n = 52 form. Sex chromosomes are negative heterochromatins. In the 2n = 60 form, a telomeric heterochromatin region was found in seven pairs of chromosomes. The sex chromosomes have centromeric heterochromatin. According to the NOR distributions of chromosomes, in 2n = 52 cytotypes, NOR was detected in the telomeric regions of four bi-armed chromosomes, while in 2n = 60 types active NOR was detected in telomeric regions of three bi-armed chromosomes.

Chromosome Banding in Amphibia. XXXV. Highly Mobile Nucleolus Organizing Regions in Craugastor fitzingeri (Anura, Craugastoridae)

A 7-year cytogenetic study on the leaf litter frog Craugastor fitzingeri from Costa Rica and Panama revealed the existence of highly mobile nucleolus organizing regions (NORs) in their genomes. Silver (Ag)-staining of the active NORs demonstrated an exceptional interindividual pattern of NOR distribution at the telomeres of the chromosomes. All individuals examined showed a different and specific NOR location in their karyotypes. Furthermore, intraindividual variation in the NOR sites was found. This observation suggested the existence of mobile NORs in C. fitzingeri. Confirmation of this phenomenon was possible by systematic FISH analysis using an 18S + 28S rDNA probe. The extremely variable number and position of the NORs in C. fitzingeri is best explained by highly mobile NORs that move freely between the telomeres of the chromosomes. These transpositions must occur preferentially in premeiotic, meiotic, or postmeiotic stages, but also at a lower incidence in the somatic tissues of the animals. It is hypothesized that transposable (mobile) elements are closely linked to the NORs or are inserted into the major 18S + 28S rDNA spacers of C. fitzingeri. When such transposable elements spread by transpositions, they can carry with them complete or partial NORs. The present study provides detailed information on various differential chromosome banding techniques, in situ hybridization experiments, chromosomal hypermethylation patterns, determination of the genome size, and analyses of restriction fragment length polymorphisms of the DNA.

Nucleolar activity in Triticum x Thinopyrum hybrids with different ploidy level

The activity of nucleolar organizer regions (NORs) and the presence of ribosomal DNA (rDNA) zones were studied in two Triticum x Thinopyrum hybrids: a hexaploid hybrid with 2n = 42 chromosomes, named trigopiro SH16 INTA, and a decaploid hybrid with 2n = 56 chromosomes, named trigopiro Don Noé INTA. The use of the pTa71 probe revealed the presence of 10 rDNA signals in both hybrids, whereas the Ag-NORs technique showed 10 signals in SH16 and 8 in Don Noé. We concluded that all trigopiro SH16 INTA NORs are active and that the activity of one NOR pair of trigopiro Don Noé INTA is suppressed. Therefore, the amphiplasty phenomenon is present in trigopiro Don Noé INTA but not in trigopiro SH16 INTA.

Nucleolar organizer regions: genomic 'dark matter' requiring illumination.

Nucleoli form around tandem arrays of a ribosomal gene repeat, termed nucleolar organizer regions (NORs). During metaphase, active NORs adopt a characteristic undercondensed morphology. Recent evidence indicates that the HMG-box-containing DNA-binding protein UBF (upstream binding factor) is directly responsible for this morphology and provides a mitotic bookmark to ensure rapid nucleolar formation beginning in telophase in human cells. This is likely to be a widely employed strategy, as UBF is present throughout metazoans. In higher eukaryotes, NORs are typically located within regions of chromosomes that form perinucleolar heterochromatin during interphase. Typically, the genomic architecture of NORs and the chromosomal regions within which they lie is very poorly described, yet recent evidence points to a role for context in their function. In Arabidopsis, NOR silencing appears to be controlled by sequences outside the rDNA (ribosomal DNA) array. Translocations reveal a role for context in the expression of the NOR on the X chromosome in Drosophila Recent work has begun on characterizing the genomic architecture of human NORs. A role for distal sequences located in perinucleolar heterochromatin has been inferred, as they exhibit a complex transcriptionally active chromatin structure. Links between rDNA genomic stability and aging in Saccharomyces cerevisiae are now well established, and indications are emerging that this is important in aging and replicative senescence in higher eukaryotes. This, combined with the fact that rDNA arrays are recombinational hot spots in cancer cells, has focused attention on DNA damage responses in NORs. The introduction of DNA double-strand breaks into rDNA arrays leads to a dramatic reorganization of nucleolar structure. Damaged rDNA repeats move from the nucleolar interior to form caps at the nucleolar periphery, presumably to facilitate repair, suggesting that the chromosomal context of human NORs contributes to their genomic stability. The inclusion of NORs and their surrounding chromosomal environments in future genome drafts now becomes a priority.

Protective effect of wheat germ agglutinin on the course of mitosis in the roots of Triticum aestivum seedlings exposed to cadmium

Effect of pretreatment with 28 nM wheat germ agglutinin (WGA) on cell divisions in the root apical meristem of 4-day-old seedlings of wheat (Triticum aestivum L.), distribution of cells among mitotic phases, cadmium-induced disruptions of normal progression through mitosis, and activity of nucleolar organizer regions (NOR) of the chromosomes was studied after 7-h-long exposure to 1 mM cadmium acetate. Pretreatment with WGA has a pronounced protective effect on divisions of root meristem cells exposed to cadmium. Progression of the cells through mitotic phases was normalized, abnormal mitoses became much less numerous, and the share of binuclear cells decreased. Activity of NOR remained at the control level that much depended on the ability of WGA to prevent reduction in cytokinin content under cadmium stress.