R‐loops mediate transcription‐associated formation of human rDNA secondary constrictions

2021 ◽  
Author(s):  
Hong Zhou ◽  
Yapei Wang ◽  
Qing Wang ◽  
Le Li ◽  
Yan Hu ◽  
...  
Keyword(s):  
Secondary Constrictions

A role for upstream binding factor in organizing ribosomal gene chromatin

2006 ◽  
Vol 73 ◽  
pp. 77-84 ◽  
Author(s):  
Jane E. Wright ◽  
Christine Mais ◽  
José-Luis Prieto ◽  
Brian McStay
Keyword(s):  
Nucleolar Organizer ◽  
Ribosomal Gene ◽  
Rna Polymerase I ◽  
Nucleolar Organizer Regions ◽  
Binding Factor ◽  
Upstream Binding Factor ◽  
Acrocentric Chromosomes ◽  
Polymerase I ◽  
Secondary Constrictions ◽  
Active Nors

Human ribosomal genes are located in NORs (nucleolar organizer regions) on the short arms of acrocentric chromosomes. During metaphase, previously active NORs appear as prominent chromosomal features termed secondary constrictions, which are achromatic in chromosome banding and positive in silver staining. The architectural RNA polymerase I transcription factor UBF (upstream binding factor) binds extensively across the ribosomal gene repeat throughout the cell cycle. Evidence that UBF underpins NOR structure is provided by an examination of cell lines in which large arrays of a heterologous UBF binding sequences are integrated at ectopic sites on human chromosomes. These arrays efficiently recruit UBF even to sites outside the nucleolus, and during metaphase form novel silver-stainable secondary constrictions, termed pseudo-NORs, that are morphologically similar to NORs.

scholarly journals Chromosomal analyses in Megalonema platanum (Siluriformes: Pimelodidae), an endangered species from South American rivers

2011 ◽  
Vol 9 (1) ◽  
pp. 177-182 ◽  
Author(s):  
Rafael Augusto de Carvalho ◽  
Sebástian Sanchez ◽  
Ana Claudia Swarça ◽  
Alberto Sergio Fenocchio ◽  
Isabel C. Martins-Santos ◽  
...  
Keyword(s):  
Diploid Number ◽  
Secondary Constriction ◽  
Centromeric Heterochromatin ◽  
Large Chromosome ◽  
South American ◽  
Terminal Position ◽  
Chromosomal Data ◽  
First Time ◽  
Secondary Constrictions ◽  
Submetacentric Pair

This study presents chromosomal data of Megalonema platanum from rio Tibagi, Paraná, Brazil and from rio Paraná, Argentina. The diploid number was equal 54 with karyotype composition of 24m+16sm+2st+12a in both populations. The AgNOR sites were detected in the terminal position of a submetacentric pair of the two analyzed populations, coinciding with secondary constrictions on the short arm of pair 15. CMA3 and FISH with 18S rDNA probe displayed fluorescent signals that correspond to the AgNOR sites and secondary constriction. The presence of a small acrocentric supernumerary chromosome can be observed in M. platanum from rio Tibagi, with centromeric heterochromatin. Others heterochromatic blocks were evidenced in the terminal position of some chromosome and one metacentric large chromosome pair, probably the first pair, showed an interstitial heterochromatin. In the population of the rio Paraná were still observed heterochromatic blocks in both ends in some chromosomes. This work brings for the first time cytogenetic date of M. platanum, which is a very rare species in the rio Paraná basin and may be endangered.

scholarly journals INVESTIGATIONS ON SECONDARY CONSTRICTIONS IN POLYGONATUM

Hereditas ◽  
2010 ◽  
Vol 35 (1) ◽  
pp. 86-108 ◽  
Author(s):  
EEVA THERMAN-SUOMALAINEN
Keyword(s):  
Secondary Constrictions

scholarly journals Q- AND C-BAND CHROMOSOME MARKERS IN INBRED STRAINS OF MUS MUSCULUS

Genetics ◽  
1976 ◽  
Vol 84 (1) ◽  
pp. 67-75
Author(s):  
D A Miller ◽  
R Tantravahi ◽  
V G Dev ◽  
O J Miller
Keyword(s):  
Mus Musculus ◽  
Inbred Strains ◽  
Normal Chromosome ◽  
Rrna Genes ◽  
Chromosome Markers ◽  
Band Region ◽  
Secondary Constrictions

ABSTRACT Differences in the number of chromosomes with secondary constrictions and in the size of the C-band region on certain chromosomes have been observed among the following inbred strains of Mus musculus: C57BL/10J, C57BR/cdJ, DBA/1J, CBA/J, BALB/cJ, and AKR. These differences are useful as indicators of the location of rRNA genes and as normal chromosome markers. The size of each C-band region appears to remain constant over many generations. Only one probable change in the size of a C-band region was found.

scholarly journals Varying division planes of secondary constrictions in spheroidal Escherichia coli cells

Microbiology ◽  
1999 ◽  
Vol 145 (5) ◽  
pp. 1015-1022 ◽  
Author(s):  
Arieh Zaritsky ◽  
Conrad L. Woldringh ◽  
Itzhak Fishov ◽  
Norbert O. E. Vischer ◽  
Monica Einav
Keyword(s):  
Escherichia Coli ◽  
Escherichia Coli Cells ◽  
Secondary Constrictions

The nucleolar cycle in man

1977 ◽  
Vol 25 (1) ◽  
pp. 103-110
Author(s):  
M. Anastassova-Kristeva
Keyword(s):  
Gene Expression ◽  
Mitotic Division ◽  
Tissue Cultures ◽  
Nucleolar Number ◽  
Satellite Chromosomes ◽  
Nucleolar Cycle ◽  
Group D ◽  
Secondary Constrictions ◽  
Nucleolus Organizers

Tissue cultures of human embryonal kidney and ovary were examined. In the nuclei of both tissues, one to ten nucleoli have been found. The maximum number of nucleoli is connected with the gene expression of rDNA of the 10 nucleolus organizers of chromosome pairs Nos. 13, 14, 15, 21 and 22, which have secondary constrictions and are the satellite chromosomes in man. The small percentage of cells with 10, 9 and 8 nucleoli is attributed to the rapid association of 3 of the homologous acrocentrics (perhaps of group D). Two of the satellite (SAT) pairs probably associate later after mitosis. The process of fusion is dynamic, resulting in one interphase nucleous—a manifestation of the association of all SAT chromosomes. Dissociation of the nucleolus occurs upon entering prophase, due to the condensation of the chromosomes and retreat of rDNA to the respective secondary constrictions. As a result, the nucleolar number increases again. The pattern of the nucleolar kinetics within the course of one mitotic division is described.

Secondary Constrictions in Human Chromosomes

1965 ◽  
Vol 4 (4-5) ◽  
pp. 261-276 ◽  
Author(s):  
Catherine G. Palmer ◽  
Sandra Funderburk
Keyword(s):  
Human Chromosomes ◽  
Secondary Constrictions

Relation of the Nucleolus to Secondary Constrictions

Nature ◽  
1939 ◽  
Vol 144 (3658) ◽  
pp. 980-980 ◽  
Author(s):  
R. RUGGLES GATES
Keyword(s):  
Secondary Constrictions

scholarly journals Studies on Metatherian Sex Chromosomes. IX. Sex Chromosomes of the Greater Glider (Marsupialia : Petauridae)

1979 ◽  
Vol 32 (3) ◽  
pp. 375 ◽  
Author(s):  
JD Murray ◽  
GM McKay ◽  
GB Sharman
Keyword(s):  
X Chromosome ◽  
Sex Chromosomes ◽  
National Park ◽  
Secondary Constriction ◽  
X Chromosomes ◽  
Cultured Fibroblasts ◽  
Multiple Sex Chromosomes ◽  
Eastern Australia ◽  
Xy Bivalent ◽  
Secondary Constrictions

The greater glider, currently but incorrectly known as Schoinobates vo/ans, is widely distributed in forested regions in eastern Australia. All animals studied from six different localities had 20 autosomes but there were four chromosomally distinct populations. At Royal National Park, N.S.W., all female greater gliders studied had 22 chromosomes including two large submetacentric X chromosomes with subterminal secondary constrictions in their longer arms. This form of X chromosome occurred also at Bondo State Forest, Myall Lakes and Coff's Harbour, N.S.W., and at Eidsvold, Qld. At Coomooboolaroo, Qld, the X chromosome was also a large submetacentric but a secondary constriction occurred in the shorter arm. Two chromosomally distinct types apparently occur in Royal National Park, one with XY m,ales as in all other populations, and one with XY1Y2 males. Y or Yb but not Y 2, chromosomes were eliminated from the bone marrow in all populations but were present in spermatogonia, primary sperrnatocytes and cultured fibroblasts. Animals from Bondo State Forest had three or more acrocentric or metacentric supernumerary chromosomes. [Other keywords: C-banding, eytotaxonomy, multiple sex chromosomes, XY bivalent.]

Étude caryologique de trois espèces d’Hypochoeris originaires d'Argentine : H. chillensis, H. microcephala var. albiflora et H. megapotamica

1994 ◽  
Vol 72 (10) ◽  
pp. 1496-1502 ◽  
Author(s):  
S. Siljak-Yakovlev ◽  
A. Bartoli ◽  
G. Roitman ◽  
N. Barghi ◽  
C. Mugnier
Keyword(s):  
Chromosome Number ◽  
Related Species ◽  
Secondary Constriction ◽  
Nucleolar Organizer ◽  
Asymmetry Index ◽  
Evolutionary Trend ◽  
Closely Related Species ◽  
Nucleolar Organizers ◽  
Morphological Differences ◽  
Secondary Constrictions

Three Hypochoeris species from Argentina with the same chromosome number (x = 4) and similar karyotypes (typically bimodal) show significant ecological and morphological differences. Comparative cytogenetic analysis was done for these taxa, producing karyotypes with correlated idiograms. The number of secondary constrictions and nucleolar organizers varied. The results from this study are discussed in terms of the mechanisms of microevolution within this group of closely related species, and in terms of the evolutionary trend in the genus and in the tribe Cichorieae. Key words: Hypochoeris, Cichorieae, bimodal karyotype, secondary constriction, nucleolar organizer, asymmetry index.

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