The Nucleolar Organizer Regions (NORs) were first described by Heitz (1931) and McClintock (1934) as weakly stained chromatin regions around which, at the end of telophase, nucleoli are reformed after their disappearance during the mitotic phase of the cell cycle. NORs, located on short arm of acrocentric chromrsomes (Chromosome number 13,14,15,21 and 22) contain ribosomal genes which encode fo...

Fluorescence in situ hybridization of Anopheles darlingi and A. nuneztovari demonstrated nucleolar organizer region activity at the end of the fourth larval instar, when the nucleolar organizer regions underwent gradual condensation. The heteromorphic sex chromosomes showed intraindividual size variation in the rDNA blocks located in the pericentromeric region and this coincided with the locati...

We have developed a procedure for sequential silver staining and in situ hybridization to analyze the relationship between the amount of rDNA present in nucleolar organizer regions, as estimated by in situ hybridization, and their level of expression, as estimated by the silver signal. For simplicity we used cells from the insectivorous mole Talpa occidentalis, which have a single pair of nucle...

BACKGROUND The relationship between the population doubling time and the quantity of silver-stained nucleolar organizer region (AgNOR) interphase proteins was studied in cell culture at three different temperatures used to modulate the cell cycle duration. METHODS After MIB 1 and AgNOR combined staining, the quantity of AgNOR proteins was measured in cycling cells by image cytometry. RESULT...

Within the Orthopteran species, those of the suborder Ensifera have been rarely studied from the cytogenetic point of view, mainly due to the difficulties for taxonomic identification of its species. The Gryllidae is the second largest family of this suborder and possesses some genera, such as Anurogryllus, that occur only on the American continents. The aim of this work was to determine the ka...

The paradoxical frog Pseudis tocantins is the only species in the Hylidae family with known heteromorphic Z and W sex chromosomes. The Z chromosome is metacentric and presents an interstitial nucleolar organizer region (NOR) on the long arm that is adjacent to a pericentromeric heterochromatic band. In contrast, the submetacentric W chromosome carries a pericentromeric NOR on the long arm, whic...

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 B(6) choromosomes pre...

Nucleolar organizer regions identified by means of an argyrophilic technique (AgNOR) were quantified by digital image analysis in 81 patients with squamous cell carcinoma of the lung. Survival rate was modeled as function of AgNOR expression by Cox regression models controlled for staging, histologic grade, age, and sex. Our results indicate that AgNOR expression has a significant prognostic ro...