The genus Mesoplodon (Cetacea: Odontoceti: Ziphiidae) is one of the few cetacean genera with the karyotype 2n = 42. The 2n = 42 karyotype of M. europaeus and M. carlhubbsi is largely consistent with the general cetacean karyotype 2n = 44, although other 2n = 42 karyotypes do not exhibit clear homologies with the general cetacean karyotype. Therefore, the chromosomes of Mesoplodon species may be...

The amniote organizer (Hensen's node) can induce a complete nervous system when grafted into a peripheral region of a host embryo. Although BMP inhibition has been implicated in neural induction, non-neural cells cannot respond to BMP antagonists unless previously exposed to a node graft for at least 5 hours before BMP inhibitors. To define signals and responses during the first 5 hours of node...

The chromosome modal number in Muscoidea Diptera is 2n=12, including five pairs of autosomes and one sex chromosome pair. Nevertheless, some species with 2n=10 chromosomes have been described, all of them from the Muscidae family. We analyzed the karyotype of some Muscidae species from different subfamilies and compared the obtained data with the karyotypes of some species of the families Calli...

A technique for staining the nucleolar organizer regions (NORs) in tumor cells applied to smears from brain tumor biopsy specimens is described. This technique provides a rapid intraoperative evaluation of the proliferative activity in cerebral neoplasms and is a valuable complement to hematoxylineosin stained smears, supporting the criteria of benignity or malignancy in these tumors.

The rDNA arrays in Drosophila contain the cis-acting nucleolus organizer regions responsible for forming the nucleolus and the genes for the 28S, 18S, and 5.8S/2S RNA components of the ribosomes and so serve a central role in protein synthesis. Mutations or alterations that affect the nucleolus organizer region have pleiotropic effects on genome regulation and development and may play a role in...

We discuss the evolutionary significance of four aberrant 18S rDNA clones that were obtained from human, chimpanzee, and gorilla DNA libraries. We show that these clones carry representatives of a small 18S rDNA pseudogene family that arose in a common ancestor of these species. Aspects of their structure and phylogenetic distribution suggest that the 18S pseudogenes no longer interact genetica...

A silver staining method was used to analyze the distribution of nucleolar organizer regions (Ag-NORs) on chromosomes of 45 wild mice (Mus musculus). The four subspecies represented were M. m. musculus, M. m. molossinus, M. m. castaneus, and M. m. bactrianus. Ag-NORs were observed near the centromeric regions of 11 chromosomes (4, 8, 9, 10, 11, 12, 15, 16, 17, 18, and 19), indicating a preponde...

OBJECTIVE To evaluate the changes induced in silver-stained nucleolar organizer regions (AgNORs) by the first fraction of a radiotherapy protocol for gynecologic cancer on exfoliated cytologic samples to predict the therapeutic success of the full protocol. STUDY DESIGN Thirteen gynecologic cancer patients who were scheduled for radiotherapy were included in the study. Cell smears were taken ...

In both pIants and animals the mechanism of ribo-somal R N A synthesis is thought to be the same, yet genetic and biochemical evidence points to a dispersed origin along chromosomal D N A in plants (1, 2, 3) and a strict localization of genes coding for ribosomal R N A in the nucleolar organizer regions of chromosomes in animals (4, 5). A precise means of locahzing ribosomal cistrons has been m...

Classical electron-microscopic techniques (enzymic digestion, EDTA regressive staining) allied with autoradiographic studies after [3H]uridine incorporation or after RNA synthesis initiated by an exogeneous RNA polymerase in the presence of tritiated GTP, enabled us to describe the fine structure and activity of the nucleolus in an established Drosophila cell line. This nucleolus is composed of...