RIBOSOMAL GENE LOCALIZATION AND DISTRIBUTION (ARRANGEMENT) WITHIN THE NUCLEOLAR ORGANIZER REGION OF ZEA MAYS

Genetics ◽  
1975 ◽  
Vol 80 (3) ◽  
pp. 505-518
Author(s):  
Samuel A Ramirez ◽  
John H Sinclair
Keyword(s):  
Zea Mays ◽  
Organizer Region ◽  
Nucleolar Organizer Region ◽  
Nucleolar Organizer ◽  
B Chromosome ◽  
Ribosomal Gene ◽  
Ribosomal Genes ◽  
Rrna Genes ◽  
Gene Localization ◽  
Chromosome 6

ABSTRACT Cytogenetic and molecular hybridization techniques were used to examine the arrangement of rRNA genes at the nucleolar organizer region (NOR) of maize. TB-6a stocks involving a reciprocal translocation between a B chromosome and the NOR of chromosome 6 were used. The amount of rDNA in the different stocks used varied from 1.5 to 4 NOR equivalents depending on the number of B6 choromosomes present. Cytological measurements show that the medial break through the NOR results in an equal partitioning of the heterochromatic knob (the NOR) between chromosome 6 and the B chromosome to which it was translocated. DNA-rRNA hybridization experiments show a linear relationship between the amount of rRNA capable of hybridizing with DNA and the number of NOR equivalents present. The data confirm McClintock's conclusion that the heterochromatic knob, rather than the constricted portion, is the true NOR region. Further, they show that the number of ribosomal genes is correlated with the amount of cytologically visible NOR, suggesting a uniform distribution of genes throughout the locus.

INTRASPECIFIC VARIATION OF RIBOSOMAL GENE REDUNDANCY IN ZEA MAYS

Genetics ◽  
1975 ◽  
Vol 80 (3) ◽  
pp. 495-504
Author(s):  
Samuel A Ramirez ◽  
John H Sinclair
Keyword(s):  
Zea Mays ◽  
Intraspecific Variation ◽  
Nuclear Dna ◽  
Higher Plants ◽  
Intraspecific Variability ◽  
Ribosomal Gene ◽  
Ribosomal Genes ◽  
Rrna Genes ◽  
Redundancy Level ◽  
Gene Redundancy

ABSTRACT Ribosomal genes in eukaryotes are highly redundant. Considerable variation in the level of redundancy among species, especially in higher plants, has been reported; but except for deletion and duplication mutants, it is generally accepted that intraspecific variability in redundancy level is small. We have examined the level of redundancy in several lines of maize by DNA-rRNA saturation hybridization. The amount of nuclear DNA which hybridizes with rRNA in the ten lines examined varied from 0.24% to 0.50%. The number of rRNA genes per diploid genome thus ranges from 1.12 × 104 to 2.32 × 104. Results also indicate that the level of redundancy is genetically transmitted.

Molecular analysis of a NOR site polymorphism in brown trout (Salmo trutta): organization of rDNA intergenic spacers

Genome ◽  
1997 ◽  
Vol 40 (6) ◽  
pp. 916-922 ◽  
Author(s):  
Jaime Castro ◽  
Laura Sánchez ◽  
Paulino Martínez ◽  
Stefania De Lucchini ◽  
Irma Nardi
Keyword(s):  
Salmo Trutta ◽  
Organizer Region ◽  
Nucleolar Organizer Region ◽  
Nucleolar Organizer ◽  
Initial Step ◽  
Molecular Organization ◽  
Rrna Genes ◽  
28S Rrna ◽  
Intergenic Spacers ◽  
Brown Trout Salmo Trutta

Using restriction endonuclease mapping, we have analyzed the organization of rDNA (DNA coding for ribosomal RNA (rRNA)) units in the salmonid fish Salmo trutta, as an initial step toward understand the molecular basis of a nucleolar organizer region (NOR) site polymorphism detected in this species. The size of the rDNA units ranged between 15 and 23 kb, with remarkable variation both within individuals and between populations. Three regions of internal tandem repetitiveness responsible for this length polymorphism were located to the intergenic spacers. NOR site polymorphic individuals showed a higher number of length classes, in some cases forming a complete 1 kb fragment ladder. The amount of rRNA genes was as much as 8-fold higher in polymorphic individuals compared with standard individuals. All individuals from the most polymorphic population showed a 14-kb insertion of unknown nature in a small proportion (below 25%) of the 28S rRNA genes.Key words: rRNA genes, repetitive elements, molecular organization, rDNA amount.

scholarly journals Effects of B chromosomes on the activity of nucleolar organizer regions in the grasshopper Eyprepocnemis plorans: activation of a latent nucleolar organizer region on a B chromosome fused to an autosome

Genome ◽  
1987 ◽  
Vol 29 (1) ◽  
pp. 116-121 ◽  
Author(s):  
J. Cabrero ◽  
J. D. Alché ◽  
J. P. M. Camacho
Keyword(s):  
Organizer Region ◽  
Nucleolar Organizer Region ◽  
Centric Fusion ◽  
Nucleolar Organizer ◽  
B Chromosome ◽  
Nucleolar Organizer Regions ◽  
Eyprepocnemis Plorans ◽  
X Chromosomes ◽  
Active Nors ◽  
Do So

Four nucleolar organizer regions (NORs) are active in standard males of the grasshopper Eyprepocnemis plorans. They are located near the centromeric regions of the S9, S10, S11, and X chromosomes. Changes in the pattern of NOR activity have been observed in the presence of a B2 type supernumerary chromosome. Males with one B show a higher mean number of active NORs per cell than do zero B males owing to significant increases in the activity of the NORs on the S11 and the X. Zero B and one B embryos, however, showed similar patterns of activity. In a male carrying a centric fusion between a B and one of the L1 chromosomes, the activation of a latent NOR, present at the telomere of the long arm of the B, parallelled a significant decrease of NOR activity on the S9 and S10 bivalents stemming from a competition between different NORs in the presence of the B. Thus, while in zero B males the activity of the S10 NOR influences that of the NORs on the X and S9 in a negative way, in one B males it does not do so, although such an influence is observed in the B–L1 fusion male where the activity of the S10 NOR again decreases significantly. On the other hand, the activities of the NORs on the S9 and S11 show a significant positive interdependence in both zero B and one B males where S11 NOR activity is increased but do not do so in the B–L1 fusion male, which shows a significant decrease in the S9 NOR activity. Key words: Eyprepocnemis plorans, B chromosome, nucleolus.

scholarly journals Comparative FISH analysis of Senna tora tandem repeats revealed insights into the chromosome dynamics in Senna

2021 ◽  
Vol 43 (3) ◽  
pp. 237-249 ◽  
Author(s):  
Thanh Dat Ta ◽  
Nomar Espinosa Waminal ◽  
Thi Hong Nguyen ◽  
Remnyl Joyce Pellerin ◽  
Hyun Hee Kim
Keyword(s):  
Tandem Repeats ◽  
Chromosomal Rearrangements ◽  
Organizer Region ◽  
Nucleolar Organizer Region ◽  
Nucleolar Organizer ◽  
Pericentromeric Region ◽  
Its2 Sequence ◽  
Fish Analysis ◽  
Chromosomal Distribution ◽  
Chromosome Dynamics

Abstract Background DNA tandem repeats (TRs) are often abundant and occupy discrete regions in eukaryotic genomes. These TRs often cause or generate chromosomal rearrangements, which, in turn, drive chromosome evolution and speciation. Tracing the chromosomal distribution of TRs could therefore provide insights into the chromosome dynamics and speciation among closely related taxa. The basic chromosome number in the genus Senna is 2n = 28, but dysploid species like Senna tora have also been observed. Objective To understand the dynamics of these TRs and their impact on S. tora dysploidization. Methods We performed a comparative fluorescence in situ hybridization (FISH) analysis among nine closely related Senna species and compared the chromosomal distribution of these repeats from a cytotaxonomic perspective by using the ITS1-5.8S-ITS2 sequence to infer phylogenetic relationships. Results Of the nine S. tora TRs, two did not show any FISH signal whereas seven TRs showed similar and contrasting patterns to other Senna species. StoTR01_86, which was localized in the pericentromeric regions in all S. tora, but not at the nucleolar organizer region (NOR) site, was colocalized at the NOR site in all species except in S. siamea. StoTR02_7_tel was mostly localized at chromosome termini, but some species had an interstitial telomeric repeat in a few chromosomes. StoTR05_180 was distributed in the subtelomeric region in most species and was highly amplified in the pericentromeric region in some species. StoTR06_159 was either absent or colocalized in the NOR site in some species, and StoIGS_463, which was localized at the NOR site in S. tora, was either absent or localized at the subtelomeric or pericentromeric regions in other species. Conclusions These data suggest that TRs play important roles in S. tora dysploidy and suggest the involvement of 45S rDNA intergenic spacers in “carrying” repeats during genome reshuffling.

scholarly journals The genomic structure of a human chromosome 22 nucleolar organizer region determined by TAR cloning

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Jung-Hyun Kim ◽  
Vladimir N. Noskov ◽  
Aleksey Y. Ogurtsov ◽  
Ramaiah Nagaraja ◽  
Nikolai Petrov ◽  
...  
Keyword(s):  
Genomic Structure ◽  
Organizer Region ◽  
Nucleolar Organizer Region ◽  
Nucleolar Organizer ◽  
Chromosome 21 ◽  
Reference Sequence ◽  
Chromosome 22 ◽  
Rdna Variation ◽  
High Level ◽  
Tar Cloning

AbstractThe rDNA clusters and flanking sequences on human chromosomes 13, 14, 15, 21 and 22 represent large gaps in the current genomic assembly. The organization and the degree of divergence of the human rDNA units within an individual nucleolar organizer region (NOR) are only partially known. To address this lacuna, we previously applied transformation-associated recombination (TAR) cloning to isolate individual rDNA units from chromosome 21. That approach revealed an unexpectedly high level of heterogeneity in human rDNA, raising the possibility of corresponding variations in ribosome dynamics. We have now applied the same strategy to analyze an entire rDNA array end-to-end from a copy of chromosome 22. Sequencing of TAR isolates provided the entire NOR sequence, including proximal and distal junctions that may be involved in nucleolar function. Comparison of the newly sequenced rDNAs to reference sequence for chromosomes 22 and 21 revealed variants that are shared in human rDNA in individuals from different ethnic groups, many of them at high frequency. Analysis infers comparable intra- and inter-individual divergence of rDNA units on the same and different chromosomes, supporting the concerted evolution of rDNA units. The results provide a route to investigate further the role of rDNA variation in nucleolar formation and in the empirical associations of nucleoli with pathology.

Nucleolar organizer region staining patterns in paraffin-embedded tissue cells from human skin cancers

2005 ◽  
Vol 32 (5) ◽  
pp. 323-328 ◽  
Author(s):  
Rosana F. Romao-Correa ◽  
Durvanei A. Maria ◽  
Mithitaka Soma ◽  
Mirian N. Sotto ◽  
Jose Antonio Sanches ◽  
...  
Keyword(s):  
Human Skin ◽  
Organizer Region ◽  
Nucleolar Organizer Region ◽  
Nucleolar Organizer ◽  
Skin Cancers ◽  
Tissue Cells

Nucleologenesis in Trypanosoma cruzi

2016 ◽  
Vol 22 (3) ◽  
pp. 621-629 ◽  
Author(s):  
Tomás Nepomuceno-Mejía ◽  
Reyna Lara-Martínez ◽  
Roberto Hernández ◽  
María de Lourdes Segura-Valdez ◽  
Luis F. Jiménez-García
Keyword(s):  
Cell Division ◽  
Trypanosoma Cruzi ◽  
Ethylenediaminetetraacetic Acid ◽  
Organizer Region ◽  
Nucleolar Organizer Region ◽  
Light And Electron Microscopy ◽  
Nucleolar Organizer ◽  
Nuclear Bodies ◽  
Nucleolar Organizer Regions ◽  
Nucleolar Material

AbstractNucleolar assembly is a cellular event that requires the synthesis and processing of ribosomal RNA, in addition to the participation of pre-nucleolar bodies (PNBs) at the end of mitosis. In mammals and plants, nucleolar biogenesis has been described in detail, but in unicellular eukaryotes it is a poorly understood process. In this study, we used light and electron microscopy cytochemical techniques to investigate the distribution of nucleolar components in the pathway of nucleolus rebuilding during closed cell division in epimastigotes of Trypanosoma cruzi, the etiologic agent of American trypanosomiasis. Silver impregnation specific for nucleolar organizer regions and an ethylenediaminetetraacetic acid regressive procedure to preferentially stain ribonucleoprotein revealed the conservation and dispersion of nucleolar material throughout the nucleoplasm during cell division. Furthermore, at the end of mitosis, the argyrophilic proteins were concentrated in the nucleolar organizer region. Unexpectedly, accumulation of nucleolar material in the form of PNBs was not visualized. We suggest that formation of the nucleolus in epimastigotes of T. cruzi occurs by a process that does not require the concentration of nucleolar material within intermediate nuclear bodies such as mammalian and plant PNBs.

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