Heterochromatin and interstitial telomeric DNA homology.

The purpose of this investigation was twofold. The first objective was to demonstrate that, in most of ten mammalian species commonly used in biomedical research, not all constitutive heterochromatin (C-bands) represents telomeric DNA. For example, the C-bands in human chromosomes, the long arm of the X and the entire Y chromosome of Chinese hamster, and most of the short arms of Peromyscus and Syrian hamster chromosomes are not telomeric DNA. In addition to the usual terminal telomeric DNA in the chromosomes of these mammalian species, the pericentromeric regions of seven or eight Syrian hamster chromosomes and all Chinese hamster chromosomes except pair one have pericentromeric regions that hybridize with telomeric DNA, some in C-bands and some not. The second objective was to describe a simple fluorescence in situ hybridization (FISH) reverse-printing procedure to produce black-and-white microphotographs of metaphase and interphase cells showing locations of telomeric DNA with no loss of resolution. Thus, at least three different types of heterochromatin (telomeric heterochromatin, nontelomeric heterochromatin and a combination of both) are present in these mammalian species, and this simple black-and-white reverse printing of telomeric FISH preparations can depict them economically without sacrificing clarity.

A high-resolution G-banding idiogram of Rattus norvegicus chromosomes.

G-banded karyotypes of Rattus norvegicus fibroblast cells at the late prophase, prometaphase, early metaphase, mid and late metaphase, and diagrammatic representation of the banding patterns at the 450-band level are presented. High-resolution G-banded rat chromosomes were prepared following the actinomycin D pretreatment technique. Silver-stained nucleolus organizer regions (Ag-NORS) were found in chromosome pairs 3, 11 and 12 of the rat karyotype.