The role of chromosomal proteins in the induction of a differential staining of sister chromatids by light

Dynamic G- and R-banding of human chromosomes for electron microscopy

Synchronized human lymphocytes were exposed to 5-bromo-2'-deoxyuridine (BrdUrd) for incorporation in either G- or R-bands. The substituted bands were revealed by monoclonal anti-BrdUrd antibodies disclosed with either gold-labeled antibodies or with the protein A-gold complex. Sharp G- or R-banding, specific for electron microscopy (EM), was obtained. These banding patterns, referred to as GB-AAu (G-bands by BrdUrd using Antibodies and gold [Au]) and RB-AAu (R-bands by BrdUrd using Antibodies and gold [Au]), resemble dynamic band patterns (GBG and RBG) much more than they do morphologic band patterns (GTG and RHG). The G- and R-band patterns allow accurate chromosome identification and karyotyping. An actual karyotype of human GB-AAu-banded chromosomes at the 750 band level, photographed in the EM, is presented. The method produces excellent band separation and band contrast. Variations in band staining intensities were noted and correlated with BrdUrd enrichment. The C-band regions were positively stained after GB-AAu banding while they were negatively stained after RB-AAu banding. Telomeres appeared heterogeneous after GB-AAu banding suggesting that part of the telomeric bands might be late replicating.

On the mechanism of differential Giemsa staining of bromodeoxyuridine-substituted chromosomes. II. Differences between the demonstration of sister chromatid differentiation and replication patterns

Experiments were performed to find out whether different mechanisms are involved in FPG-(fluorescent plus Giemsa) staining for the demonstration of replication patterns and sister chromatid differentiation (SCD) after bromodeoxyuridine (BrdU)-substitution of V79 Chinese hamster chromosomes. The influence of variations of the staining procedure on the quality of both SCD and replication patterns was comparatively investigated and differences in the demonstration of these two phenomena within the same chromosome were studied using various BrdU-labeling protocols. The results show that at least graduated differences exist. For a good differentiation of replication patterns a stronger FPG-treatment is necessary than it is for SCD. Partial BrdU substitution only leads to replication patterns in the next mitosis. A further round of replication either in the presence or absence of BrdU causes a reduced staining of the complete chromatid and three-way differentiation is seen in third generation mitoses. These results support the view that alterations of chromosomal proteins during BrdU-incorporation and replication of BrdU-substituted DNA are decisive for differential staining.

Considerations on the mechanism of differential Giemsa staining of BrdU-substituted chromosomes

The staining properties of unifilarly bromodeoxyuridine (BrdU)-substituted chromatids were compared using fluorescent-plus-Giemsa (FPG) staining methods. It was found that the staining intensity of chromatids which had incorporated BrdU in the next to last S-phase is less than that of chromatids whose BrdU-containing strand came from the last cell cycle. Thus, FPG-staining is not a function of the number of BrdU-substituted DNA strands alone. These findings lead to the conclusion that the primary point of action of PFG staining leading to sister chromatid differentiation (SCD) are chromosomal proteins which have been altered in the replication of BrdU-substituted DNA and that the demonstration of the SCD and replication patterns with the same staining procedure is based on different mechanisms.

DNA lysis is involved in the simplified fluorescence plus Giemsa method for differential staining of sister chromatids

The DNA labelling of the bifilarly 5-bromodeoxyuridine- to-substituted chromatid decreased relative to that of the unifilarly substituted chromatid with increasing duration of HB pretreatment (Hoechst 33258 plus black light at 55 degrees C). Sister chromatid differential staining was detected by Giemsa as well as a DNA-specific dye, ethidium bromide, after 4 s of HB pretreatment. The contrast of sister chromatid differential staining was improved with increased duration of HB pretreatment or by incubation with exonucleases. Hydrogen donors such as cysteamine, cysteine, and L-ascorbic acid inhibited the HB pretreatment, but this inhibition could be overcome by increasing the duration of HB pretreatment.

High-resolution analysis of Allium cepa chromosome replication by an FPG technique

In Allium cepa meristematic cells, BrdU incorporation into late-replicating DNA and its detection by FPG technique has shown to allow the visualization of characteristic late replicated segments (LRS) in metaphase chromosomes not detected till now. Since these LRS have very similar characteristics with the 'dot-like' exchanges reported previously in this system, they seem to represent a new support for the idea of a regular organization of chromatin in metaphase.