Distamycin A/DAPI staining and sequential C-banding of human lymphocyte chromosomes reveals the regular occurrence of differentially staining subfractions of chromosome 9 constitutive heterochromatin. These subfractions are regionally organized as two subsegments: a distal one, which fluoresces brightly with DAPI after preincubation with distamycin A and a proximal one, which stains intensely with Giemsa after sequential C-banding. Observations are presented that indicate an occasionally independent genetic behavior of these heterochromatin subfractions.
Using DAPI staining after pretreatment with distamycin A we detected a familial deficiency of chromosome 16 heterochromatin. A distinct positively staining band, however, was seen after C-banding. Thus, by using these different heterochromatin staining methods, heterogeneity of the constitutive heterochromatin in the centromeric region of human chromosome 16 was indicated. The same C-banding procedure was also applied to a previously described familial deficiency of chromosome 9 heterochromatin evidenced using distamycin A/DAPI staining and G 11 staining (Buys et al., 1979). In this case a C-band appeared to be virtually absent on the relevant chromosome. These staining methods may be valuable tools in the study of chromosome polymorphisms.
The use of a combination of transmitted light and epiluminescence after silver and fluorescent staining of chromosome preparations makes it possible to achieve simultaneous visualization of silver-stained NORs and flourescent chromosomes. This technique permits exact localization of silver precipitates on normal and BrdU-substituted chromosomes. After previous silver impregnation, fluorescent staining by actinomycin-daunomycin-DAPI was used to induce a banding pattern that enables identification of specific chromosomes while observing silver-stained NORs at the same time. Application of this method to a Down's syndrome patient revealed a 21/21 Robertsonian translocation with NOR'S eliminated.
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