scholarly journals Holocentric Chromosomes of Luzula elegans Are Characterized by a Longitudinal Centromere Groove, Chromosome Bending, and a Terminal Nucleolus Organizer Region

2011 ◽  
Vol 134 (3) ◽  
pp. 220-228 ◽  
Author(s):  
S. Heckmann ◽  
E. Schroeder-Reiter ◽  
K. Kumke ◽  
L. Ma ◽  
K. Nagaki ◽  
...  
Keyword(s):  
Organizer Region ◽  
Nucleolus Organizer Region ◽  
Nucleolus Organizer ◽  
Holocentric Chromosomes

Meiotic behaviour of the holocentric chromosomes of Nezara viridula (Insecta, Heteroptera) analysed by C-banding and silver impregnation

1985 ◽  
Vol 27 (5) ◽  
pp. 491-497 ◽  
Author(s):  
J. P. M. Camacho ◽  
J. Belda ◽  
J. Cabrero
Keyword(s):  
Organizer Region ◽  
Nucleolus Organizer Region ◽  
Nucleolus Organizer ◽  
Silver Impregnation ◽  
Nezara Viridula ◽  
Holocentric Chromosomes ◽  
Cytological Analysis ◽  
C Banding ◽  
I Cells ◽  
Do So

While silver impregnation reveals the presence of kinetochores in monocentric chromosomes, it does not do so in the holocentric system of Nezara viridula. Here, C-banding and silver impregnation techniques reveal that C-heterochromatin is present in the greater part of the Y chromosome and at the nucleolus organizer region (NOR) of the largest autosome (A 1) and in the extra NOR located in the X chromosome of a single exceptional male. Furthermore, one telomere of each autosome appeared lightly C-banded. The largest, A1, bivalent shows chiasmata almost always located at the chromosome ends. This bivalent may orient axially or equatorially in metaphase I cells depending on whether it carries a single chiasma or two chiasmata, respectively. From our cytological analysis we deduce that centromeric activity is preferentially located at the two telomeric ends and that the presence of chiasmata at an end excludes such activity.Key words: diffuse centromere, C-banding, holocentric, insect chromosomes.

Mapping of the nucleolus organizer region on chromosome 4 inArabidopsis thaliana

1996 ◽  
Vol 250 (1) ◽  
pp. 123-128
Author(s):  
Georg Haberer ◽  
Thilo C. Fischer ◽  
Ramón A. Torres-Ruiz
Keyword(s):  
Organizer Region ◽  
Nucleolus Organizer Region ◽  
Nucleolus Organizer ◽  
Chromosome 4

Hybrid ape offspring of a mating of gibbon and siamang

Science ◽  
1979 ◽  
Vol 205 (4403) ◽  
pp. 308-310 ◽  
Author(s):  
RH Myers ◽  
DA Shafer
Keyword(s):  
Parental Species ◽  
Organizer Region ◽  
Nucleolus Organizer Region ◽  
Structural Rearrangement ◽  
Female Offspring ◽  
Nucleolus Organizer ◽  
Single Chromosome ◽  
Symphalangus Syndactylus ◽  
Hylobates Moloch ◽  
Lesser Apes

The serendipitous mating of a male gibbon, Hylobates moloch, and a female siamang, Symphalangus syndactylus, has produced two female offspring born 1 year apart. The hybrid karyotype of 47 chromosomes comprises the haploid complements of the parental species, 22 for the gibbon and 25 for the siamang. Chromosomal G and C banding comparisons revealed no clear homologies between the parental karyotypes except for the single chromosome in each species containing the nucleolus organizer region. The lack of homology suggests that the structural rearrangement of chromosomes has played a major role in the process of speciation for these lesser apes.

scholarly journals The relationship between position and expression of genes on the kangaroo X chromosome suggests a tissue-specific spread of inactivation from a single control site

1988 ◽  
Vol 51 (2) ◽  
pp. 103-109 ◽  
Author(s):  
Jennifer A. Marshall Graves ◽  
Garey W. Dawson
Keyword(s):  
Alternative Hypothesis ◽  
Organizer Region ◽  
Nucleolus Organizer Region ◽  
Control Site ◽  
Specific Pattern ◽  
Nucleolus Organizer ◽  
Tissue Specific ◽  
Expression Of Genes ◽  
Control Locus ◽  
The Relationship

SummaryIn marsupials, X chromosome inactivation is paternal and incomplete. The tissue-specific pattern of inactivation of X-linked loci (G6PD, PGK, GLA) has been attributed to a piecemeal inactivation of different regions of the X. We here propose an alternative hypothesis, in which inactivation of the marsupial X is a chromosome-wide event, but is differentially regulated in different tissues. This hypothesis was suggested by the relationship between the positions and activity of genes on the kangaroo paternal X. In the absence of an HPRT polymorphism, we have used somatic cell hybridization to assess the activity of the paternal HPRT allele in lymphocytes and fibroblasts. The absence of the paternal X, and of the paternal forms of G6PD or PGK, from 33 cell hybrids made by fusing HPRT-deficient rodent cells with lymphocytes or fibroblasts of heterozygous females, suggests that the HPRT gene on the paternal X is inactive in both tissues and therefore not selectable. Since HPRT is located medially on the Xq near GLA, which shares the same characteristics of activity, we suggest that the locus-specific and tissue-specific patterns of activity result from a differential spread of inactivation from a single control locus, located near HPRT and GLA, outwards in both directions to G6PD and PGK. The nucleolus organizer region on the short arm does not seem to be part of the inactivated unit.

scholarly journals Characterization of AtNUC-L1 Reveals a Central Role of Nucleolin in Nucleolus Organization and Silencing of AtNUC-L2 Gene in Arabidopsis

2007 ◽  
Vol 18 (2) ◽  
pp. 369-379 ◽  
Author(s):  
Frederic Pontvianne ◽  
Isabel Matía ◽  
Julien Douet ◽  
Sylvette Tourmente ◽  
Francisco J. Medina ◽  
...  
Keyword(s):  
Ribosome Biogenesis ◽  
Organizer Region ◽  
Nucleolus Organizer Region ◽  
Normal Growth ◽  
Growth Conditions ◽  
Nucleolus Organizer ◽  
Multifunctional Protein ◽  
Eukaryotic Organism ◽  
Model Plant Arabidopsis Thaliana ◽  
Fibrillar Component

Nucleolin is one of the most abundant protein in the nucleolus and is a multifunctional protein involved in different steps of ribosome biogenesis. In contrast to animals and yeast, the genome of the model plant Arabidopsis thaliana encodes two nucleolin-like proteins, AtNUC-L1 and AtNUC-L2. However, only the AtNUC-L1 gene is ubiquitously expressed in normal growth conditions. Disruption of this AtNUC-L1 gene leads to severe plant growth and development defects. AtNUC-L1 is localized in the nucleolus, mainly in the dense fibrillar component. Absence of this protein in Atnuc-L1 plants induces nucleolar disorganization, nucleolus organizer region decondensation, and affects the accumulation levels of pre-rRNA precursors. Remarkably, in Atnuc-L1 plants the AtNUC-L2 gene is activated, suggesting that AtNUC-L2 might rescue, at least partially, the loss of AtNUC-L1. This work is the first description of a higher eukaryotic organism with a disrupted nucleolin-like gene and defines a new role for nucleolin in nucleolus structure and rDNA chromatin organization.

scholarly journals Discovery of Putative XX/XY Male Heterogamety in Emydura subglobosa Turtles Exposes a Novel Trajectory of Sex Chromosome Evolution in Emydura

2019 ◽  
Vol 158 (3) ◽  
pp. 160-169 ◽  
Author(s):  
LingSze Lee ◽  
Eugenia E. Montiel ◽  
Nicole Valenzuela
Keyword(s):  
Sex Determination ◽  
Sex Chromosome ◽  
Organizer Region ◽  
Nucleolus Organizer Region ◽  
Molecular Cytogenetics ◽  
Nucleolus Organizer ◽  
Model Organisms ◽  
Comparative Genome Hybridization ◽  
Evolutionary Trajectory ◽  
Genotypic Sex Determination

The discovery of sex chromosome systems in non-model organisms has elicited growing recognition that sex chromosomes evolved via diverse paths that are not fully elucidated. Lineages with labile sex determination, such as turtles, hold critical cues, yet data are skewed toward hide-neck turtles (suborder Cryptodira) and scant for side-neck turtles (suborder Pleurodira). Here, we used classic and molecular cytogenetics to investigate Emydura subglobosa (ESU), an unstudied side-neck turtle with genotypic sex determination from the family Chelidae, where extensive morphological divergence exists among XX/XY systems. Our data represent the first cytogenetic description for ESU. Similarities were found between ESU and E. macquarii (EMA), such as identical chromosome number (2n = 50), a single and dimorphic nucleolus organizer region (NOR) localized in a microchromosome pair (ESU14) of both sexes (detected via FISH of 18S rDNA). Only the larger NOR is active (detected by silver staining). As in EMA, comparative genome hybridization revealed putative macro XX/XY chromosomes in ESU (the 4th largest pair). Our comparative analyses and revaluation of previous data strongly support the hypothesis that Emydura's XX/XY system evolved via fusion of an ancestral micro-Y (retained by Chelodina longicollis) onto a macro-autosome. This evolutionary trajectory differs from the purported independent evolution of XX/XY from separate ancestral autosomes in Chelodina and Emydura that was previously reported. Our data permit dating this Y-autosome fusion to at least the split of Emydura around 45 Mya and add critical information about the evolution of the remarkable diversity of sex-determining mechanisms in turtles, reptiles, and vertebrates.

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