A comparison between quinacrine fluorescence banding and 3H-thymidine incorporation patterns in human chromosomes

Analysis of chromosome replication by a BrdU antibody technique

Chromosome replication was studied without synchronization in human lymphocyte and amniotic cell cultures visualizing very short 5-bromodeoxyuridine (BrdU) pulses by an immunologic technique (BAT). The findings agree in general with those facts known from earlier BrdU staining techniques. The very high sensitivity of BAT was shown to allow the detection of replication in a band where 1 in 200 nucleotides is replaced by BrdU. The main observations are: though the replication patterns after BAT appear strange the bands correspond to those described by the Paris Conference (1971). At the beginning of the S-phase a stepwise onset of replication in only a subset of R-bands is confirmed. There is a considerable difference in the sensitivity between early and late S (SE and SL) for the detection of BrdU pulses. This difference probably reflects a different spatial arrangement of chromatin in R-bands as compared with G-bands below the level of cytogenetic analysis. The use of short pulses did not reveal any additional subdivision of SE or SL. The correspondence between chromosomal bands and replicon clusters is discussed briefly with respect to the different time they need for replication.

Simultaneous production of R-bands and either replication patterns or sister chromatid differentiation

The dye triplet chromomycin/methyl green/DAPI and some related dye combinations were applied to bromodeoxyuridine (BrdU)-substituted and non-substituted chromosomes. In both kinds of chromosome preparations, tri-staining followed by observation at pH 7 resulted in well defined R-bands (excitation wavelength 436 nm) and a mixed DA-DAPI/Q-banding pattern (360 nm). Two approaches have given satisfactory expression both of reverse bands and of the differential BrdU-substitution present in metaphase chromosomes: (1) direct tri-staining at pH 7 and mounting of the preparations at pH 11; or (2) pretreatment of the preparations with Hoechst 33258 plus UV and hot buffer followed by tri-staining and mounting at pH 7. These methods should prove useful for routine chromosome analysis and, in combination with BrdU-labelling, in studies of chromosome structure and replication.

Description of a chromosome replication unit in individual prematurely condensed human S-phase chromosomes

Mammalian chromosome replication was studied by the aid of premature chromosome condensation (PCC). After induction of PCC the sites of DNA replication appear as "gaps" between condensed chromosomal regions. These condensed particles are unineme before and bineme after DNA replication. The two phases are due mainly to the unineme or bineme nature of the particles. During early S-phase almost all particles are unimene, during late S-phase they are bineme and there is only one transitory stage between these two main stages. Premature chromosome condensation was studied in detail on a specific human chromosome 22 which is marked by its heterochromatin constitution. This led to easy identification of these elements in S-phase PCC (S-PCC) preparations. For each stage of the S-phase there was a reproducible pattern of condensed chromosomal particles making up the whole chromosome. The number of these particles was rather limited and a complementary pattern was found in early versus late S-phase. The pattern of early S-PCC corresponded to the banding pattern of G-banded prometaphase chromosomes; the pattern of late S-PCC, to R-banded prometaphase chromosomes. Thus, "gaps" and condensed particles as observed after PCC induction are obviously homologous to chromosome replication units. Replication of constitutive heterochromatin occurred during the very late S-phase. During this stage PCC induction led to condensation of the heterochromatin into several small, highly fluorescent particles.

Three levels of G-band differentiation

G-band "fusions" in the more contracted chromosomes, and G-band "splittings" in the longer chromosomes, have been cited directly or by implication to be natural cyclical states of human chromosomes. This report presents three levels of G-band differentiation producted by a single techinque, and compares them with three corresponding levels of R-band differentiation reported by others. It argues for the possibility of artifactural band "fusion" mechanisms in the more contracted chromosomes.

Genetics of aneuoploidy in man reconsidered by banding studies

The effects of aneuploidy are only partially known in man, but the information available suggests that they are remarkably similar to those in Drosophila melanogaster. The fractions of the haploid genome that can be tolerated in three doses and in one dose approach 7 and 3%, respectively. Hypoploidy is more deleterious than hyperploidy. The phenotypic effects of aneuploidy result in an 'aneuploid syndrome' of developmental, mental and growth retardation and multiple malformations. Even if upon closer scrutiny a recognizable collection of dysmorphisms can be detected in some chromosomal imbalances, specific phenotypes result only as the consequence of changes in dosage-sensitive loci. The aneuploidy of man was approached by chromosomal band studies. Available data suggest that R bands may be rich in functional DNA. The proportion of R bands involved in viable imbalances was calculated, and it is concluded that nearly all chromosomal arms tolerate trisomies or monosomies of a proportion of their R band content. This evidence and the demonstration of the involvement of proportionally similar quantities of band type in viable aneuploidies contrast with the idea that imbalances with a higher R band proportion have less chances of survival. Thus band patterns seem to be adequate to provide empirical clinical phenotypes but inadequate to reflect the genetic make-up of a given chromosome.

[Discontinued treatment with BudR and staining with acridine orange: observation of R- or Q- or intermediary banding (author's transl)]

Discontinued treatments with BudR at different periods of the cellular cycle produce various chromosome banding after staining with acridine orange. In particular, it is possible to observe R- or Q- or an intermediary banding, simply by varying the time of incorporation of BudR. This implies that the amount of AT or GC bases present locally in DNA is not directly responsible for the banding observed. Furthermore it appears that a precise correlation exists between replication and R- or Q-banding: the DNA located at each group of bands replicates either early (R-bands) or late (Q-bands). But these timings overlap towards the middle of phase S: if the treatment is given at that time, it is possible to observe aspects intermediary between Q and R.

Chromosomes and DNA of Mus: terminal DNA synthetic sequences in three species

The DNA replication patterns of the terminal S phase of three species of Mus were analyzed by tritiated thymidine autoradiography. The centromeric heterochromatin of M. fulvidiventris is the latest component to finish DNA synthesis. The Y chromosome finishes replication earlier than the centromeric heterochromatin. The centromeric heterochromatin of M. musculus, on the other hand, is not the latest component to finish DNA synthesis. At the very late S phase, grains are found in the euchromatic arms instead of the heterochromatic areas. The "hot X" and the "hot Y" can be identified in the majority of, but not all, cases. The heterochromatic short arms of the autosomes in M. dunni finish DNA replication earlier than many areas in the euchromatic long arms and the heterochromatin of the sex chromosomes. This indicates that in M. dunni there are at least two types of heterochromatin. The late-replicating zones in the euchromatic long arms are distinctly banded. This banded grain pattern can be seen in all Mus species observed, but in M. dunni it is most exaggerated. Late-replicating chromosome segments can be demonstrated also by 2+ cycles of BUdR incorporation and Giemsa staining.