Mammalian chromosomes G-banded in four minutes

The involvement of nucleosomes in Giemsa staining of chromosomes. A new hypothesis on the banding mechanism

A new hypothesis is proposed on the involvement of nucleosomes in Giemsa banding of chromosomes. Giemsa staining as well as the concomitant swelling can be explained as an insertion of the triple charged hydrophobic dye complex between the negatively-charged super-coiled helical DNA and the denatured histone cores of the nucleosomes still present in the fixed chromosomes. New cytochemical data and recent results from biochemical literature on nucleosomes are presented in support of this hypothesis. Chromosomes are stained by the Giemsa procedure in a purple (magenta) colour. Giemsa staining of DNA and histone (isolated or in a simple mixture) in model experiments results in different colours, indicating that a higher order configuration of these chromosomal components lies at the basis of the Giemsa method. Cytophotometry of Giemsa dye absorbance of chromosomes shows that the banding in the case of saline pretreatment is due to a relative absence of the complex in the faintly coloured bands (interbands). Pretreatment with trypsin results in an increase in Giemsa dye uptake in the stained bands. Cytophotometric measurements of free phosphate groups before and after pretreatment with saline, reveal a blocking of about half of the free phosphate groups indicating that a substantial number of free amino groups is still present in the fixed chromosomes. Glutaraldehyde treatment inhibited Giemsa-banding irreversibly while the formaldehyde-induced disappearance of the bands could be restored by a washing procedure. These results correlate with those of biochemical nucleosome studies using the same aldehydes. Based on these findings and on the known properties of nucleosomes, a mechanism is proposed that explains the collapse of the chromosome structure when fixed chromosomes are transferred to aqueous buffer solutions. During homogeneous Giemsa staining reswelling of the unpretreated chromosome is explained by insertion of the hydrophobic Giemsa complex between the hydrophobic nucleosome cores and the superhelix DNA. Selective Giemsa staining of the AT-enriched bands after saline pretreatment is thought to be due to the, biochemically well-documented, higher affinity of arginine-rich proteins present in the core histones for GC-enriched DNA, which prevents the insertion of the Giemsa complex in the interbands. Production of Giemsa bands by trypsin pretreatment can be related to the action of this enzyme on the H1 histones and subsequent charge rearrangements.(ABSTRACT TRUNCATED AT 400 WORDS)

Assignment of the haemophilia B (factor IX) locus to the q26-qter region of the X chromosome

Two independent approaches have provided an assignment for the factor IX (Haemophilia B) locus to Xq26-qter, the distal region of the X chromosome long arm. Cloned DNA sequences of the gene were hybridized to restriction enzyme digests of DNA prepared from a series of somatic cell hybrids containing different X-chromosomal regions and also in situ to prepared metaphase chromosomes.

De novo translocation heterozygote with three reciprocal translocations

An extremely rare case of a child with three balanced reciprocal translocations involving six different autosomes is described. These abnormalities have apparently arisen de novo and seem to have only relatively minor phenotypic effects. The meiotic possibilities are discussed and cytogenetic markers suggest that the damage may have occurred in a paternal gamete.

A complex double translocation involving four chromosomes and five breakpoints in a child with mild mental retardation

A 6-year-old boy with speech delay and mild mental retardation (IQ 82) was found to have a complex double translocation involving four chromosomes and a total of five breakpoints, two being on the same arm. This resulted in the karyotype 46,XY,t(2;4;7)(7;8)(q14;q31;q11q22;q13). As far as the authors are aware this is the first time that such a complex double translocation has been reported. Both parents had normal karyotypes.

The heterogeneity of the 5q--chromosome marker in refractory anemia

A patient presenting with an unusual case of refactory anemia is described in whom acquired markers originating from chromosomes No. 5 and 8 are identified by G- and sequential C-banding. Comparison with various published illustrations of chromosome No. 5 deletions in this general broad category of disease raises the possibility that karyotypic misclassification in cases of absent or substandard banding (typical of bone marrow) may help to explain the considerable variation in size and morphology of the 5q--marker.

An unusual karyotype in preleukemia

A case of a myeloproliferative disorder classified as preleukemia is described in which the patient developed a single, complicated, abnormal karyotype in 100% of the bone marrow cells (45, XY, -2, -5, -7, -8, -11, -12, -13, -14, + t(2;5), +t(11;12), +t(16;17), +17, plus three or four dicentric markers). The possible significance of these unusual, if not unique, chromosome changes is discussed in relation to hematologic and clinical findings and with particular reference to the existing nonrandom patterns of chromosome changes in myeloproliferative disorders and acute nonlymphoblastic leukemias.

Reciprocal translocation and the Philadelphia chromosome

We examined metaphases from three patients with chronic myeloid leukaemia and a typical Philadelphia chromosome with one chromosome 9 as the recipient to determine whether the 9q+22q- translocation is reciprocal. Good quality G-banded photographs of the chromosomes concerned were subjected to light absorption density analysis. This provided enlarged tracings corresponding to the relevant chromosome regions and so facilitated accurate measurement. This technique has unambiguously shown that the typical Philadelphia chromosome results from a reciprocal translocation and that probably no material is gained or lost in the exchange. Furthermorein a total of six patients for whom sequential G and C banding was performed, the chromosome 9 with the largest block of centromeric heterochromatin received the translocated material. We offer tentative explanations for this curious observation.

Cytogenetic study of 10 cases of infectious mononucleosis

Cytogenetic analysis of 10 cases of infectious mononucleosis has revealed increased damage in the form of chromosome breakage and aberrations typical of viral infection, but in addition a few cells were consistently found to harbour a deleted number 22, similar tsponse to the mitogen phytohaemagglutinin is suggested. This inhibitor appears to have a reversible action on the patient's own lymphocytes but no inhibitory effect on control lymphocytes.

Variation in the Philadelphia chromosome

Cytogenetic study of 17 cases of chronic myeloid leukaemia has shown that the Philadelphia chromosome is a variable entity, differing in size and banding pattern between individuals.