nucleolar organizer regions (nor) are defined as nucleolar components containing a set of argyrophilic proteins which are selectively stained by colloidal silver nitrate staining. although studies have shown that the number of nor dots or particles is directly related to the rapidity of cell proliferation in cancer cells, prognostic or diagnostic value of nor remains controversial. the aim of t...

The short arms of the five acrocentric human chromosomes harbor sequences that direct the assembly and function of the nucleolus, one of the key functional domains of the nucleus, yet they are absent from the current human genome assembly. Here we describe the genomic architecture of these human nucleolar organizers. Sequences distal and proximal to ribosomal gene arrays are conserved among the...

In contrast to total cell irradiation, local UV-microbeam irradiation can stimulate a significant diminution in the irradiated mature nucleoli in interphase mammalian cells in culture. This diminution is accompanied by the concomitant expansion of the unirradiated nucleoli within the same nucleus, and the total nucleolar volume per nucleus does not change appreciably. It is suggested that these...

The epithelium of the Spemann organizer plays an important role in embryonic axis formation and transplantation experiments have shown that epithelial organizer cells have potent axis-inducing potential. Known axis-inducing molecules like noggin and chordin are not expressed in the epithelium and cannot account for its inductive properties. Xwnt-11 is expressed in the epithelium but has only po...

The transition from telophase to the G I period of interphase includes the process of nucleolar reorganization in each of the daughter nuclei, and it has been demonstrated by the classic studies of Heitz (13) and McClintock (17) that only specific regions of particular chromosomes in each karyotype are involved in the formation of new nucleoli . On the other hand, a number of studies revealed t...

A cytogenetic study was conducted on five species of the genus Pimelodus collected from various regions in Brazil: Pimelodus heraldoi, Pimelodus sp, Pimelodus argenteus, P. maculatus and P. mysteriosus. All the species had 2n=56 chromosomes. AgNOR was found in one pair of subtelocentric (ST) chromosomes with staining at the terminal position in all the five species. However, Pimelodus sp, P. he...

Silver staining at the electron microscopic level of the nucleolar organizers was carried out on Xenopus laevis oocytes at various stages of oogenesis. The results indicate that a positive reaction takes place exclusively in the dense fibrillar component of the extrachromosomal nucleoli. This constituent undergoes morphological changes of distribution and architecture, which have been correlate...

Cytogenetic studies were carried out on samples of Parapteronotus hasemani, Sternarchogiton preto and Sternarchorhamphus muelleri (Apteronotidae, Gymnotiformes) from the Amazon basin. The first two species exhibited both a 2n = 52 karyotype, but differed in their karyotypic formulae, distribution of constitutive heterochromatin, and chromosomal location of the NOR. The third species, Sternarcho...

AIM   To clinically and histopathologically evaluate the anti-inflammatory effect of 0.2% hyaluronan gel alone and with mechanical therapy on gingivitis. The argyrophilic nucleolar organizer region staining technique was attempted to routinely determine its diagnostic and prognostic dependability for periodontal lesions. METHODS   In each of the 28 gingivitis patients, the four quadrants were...

The fish genus Astyanax is widespread throughout the Neotropical region and is one of the most species-rich genera of the Characiformes. Cytogenetic studies of Astyanax have revealed marked intra- and interspecific diversity, with the identification of various species complexes. In this report, we describe the karyotypic structure of two sympatric species of Astyanax (Astyanax sp. and Astyanax ...