In order to assess the prognostic significance of silver-stained nucleolar organizer region (AgNOR) proteins, a standardised analysis has been performed on 34 ocular globes with choroidal melanomas. On formalin-fixed paraffin-embedded sections, the visualisation and quantification of AgNORs were achieved according to the guidelines of the Committee on AgNOR Quantification (1995); statistical an...

The nucleolus is the site of rRNA transcription, pre-rRNA processing and ribosome subunit assembly. The nucleolus assembles around clusters of ribosomal gene repeats during late telophase, persists throughout interphase and then disassembles as cells enter mitosis. The initial step in nucleolar formation is ribosomal gene transcription, which is mediated by Pol I (RNA polymerase I) and its asso...

Karyotype, C-banding and nucleolar organizer regions (NORs) characteristics of nine Rana ridibunda samples collected from Konya (Meram, Beyşehir, Hadim) province were examined. The diploid number of chromosomes (2n) and the fundamental number of chromosome arms (FN) were determined as 26 and 52, respectively. All of the chromosomes of this species have centromeric constitutive heterochromatin (...

By the time ofMontgomery's classic paper on the nucleolus in 1898 (1), there were already 700 or so articles with observations on this nuclear organelle, beginning with a study by Fontana in 1781 entitled "Venom of Vipers." The early cytological emphasis on the nucleolus undoubtedly was due to the high visibility of the organelle in interphase nuclei ofmost cell types ; however, the fact that n...

Crossing two parental plants carrying two types of extra chromosomes, 2n+2(5L*7S) by 2n+3(2S*2S) permitted effective selection for individuals with up to eight 2S*2S chromosomes in later generations. The crossing of 2n + 3(2S*2S) by 2n+1( 8S*8L) and by the wild tomato relative, diploid L. pimpinellifolium , produced plants with up to four extra chromosomes. The tolerance of 2S*2S chromosomes th...

The organization of chromosomes is important for various biological processes and is involved in the formation of rearrangements often observed in cancer. In mammals, chromosomes are organized in territories that are radially positioned in the nucleus. However, it remains unclear whether chromosomes are organized relative to each other. Here, we examine the nuclear arrangement of 10 chromosomes...

Karyotypic data are presented for two sympatric Corydoras species of the Lagoa Dourada, namely, C. ehrhadti and C. paleatus, which are found in the upper Tibagi river basin (Ponta Grossa, State of Paraná, Brazil). The same diploid number and karyotypic formula were observed in both species/populations. A great similarity in the constitutive heterochromatin distribution and in the activity of nu...

Molecular studies of six species from the ancient extant seed plant Cycas, covering a wide range of its morphological diversity and all major areas of distribution, revealed a high level of intra-individual polymorphism of the internal transcribed spacer (ITS1, 5.8S, and ITS2) region, indicative of incomplete nrDNA concerted evolution. Through a range of comparisons of sequence characteristics ...

The ultrastructure of embryonic root cells of Zea mays was studied from the quiescent stage (dry seed) to 72 h of germination. Semithin and ultrathin sections of tissues fixed with only glutaraldehyde and embedded in Epon were observed after usual section staining and after cytochemical reactions specific for DNA or preferential for ribonucleoproteiNS. In quiescent cells, dense chromatin forms ...

Dominance of a 5-azacytidine-substituted nucleolar organizer region (AZA NOR) over another with normal DNA when confined to a common nucleus or to different nuclei in a common cell was studied in Allium cepa L. root meristems. AZA administration took place for one S period. The assessment of NOR dominance was done either in early Gi (nucleologenesis) or later in interphase (mature nucleoli). At...