Latent NORs in the species Pycnogaster cucullata (Orthoptera)

Abstract

The chromosomal location of the ribosomal cistrons 18 + 26S and 5S has been determined in spermatocytes of two cytological races of Pycnogaster cucullata by in situ hybridization using molecular probes from both types of rDNA. A comparative analysis with previous results suggested the existence of more 18+ 26S rDNA sites than active NORs as shown by silver impregnation, but 58 rDNA sites are outside the NORs. Thus, different categories of latent NORs have been shown in this specialised cell type which are discussed in relation to the evolutionary process of differentiation in this species.

Chromosome study in Schistocerca (Orthoptera-Acrididae-Cyrtacanthacridinae): karyotypes and distribution patterns of constitutive heterochromatin and nucleolus organizer regions (NORs)

“…In grasshoppers, chromosome localization of rDNA genes by FISH has been performed in Acrididae (López-León et al, 1999;Santos et al, 1990;Vaughn et al, 1999) and Romaleidae (Souza et al, 1998;Souza et al, 2003). Variation in the distribution of rDNA sites and/or Ag-NORs, as we observed in S. flavofasciata and S. pallens, have been found in many insect species pointing to the importance of these patterns as phylogenetic markers in the genus Schistocerca.…”

“…C-banding and Ag-NOR staining have been of great importance for inter and intra-specific characterization and karyotypic differentiation in grasshoppers (Santos el al., 1983, Cabrero and Camacho 1986a, 1986bSouza and Kido, 1995;Pereira and Souza, 2000;Rocha et al, 2004). Fluorochrome staining and fluorescent in situ hybridization (FISH) have also been used to, respectively, map AT-and GC-rich chromosome regions and locate ribosomal genes (López-León et al, 1999;Santos et al, 1990;Souza et al, 1998;Pereira and Souza 2000;Souza et al, 2003).…”

Transcriptional Activity of Translocated NORs in Barley (Hordeum VulgareL.)

“…Because of its high resolution, the use of in situ hybridization with a ribosomal DnA probe can provide precise detection of the total (active and inactive) rDnA clusters, even when the ribosomal genes are present in only minute amounts. For example, some previously undetected rDnA loci have been demonstrated by the in situ hybridization technique (8), some of them being inactive (30,50).…”