G-band-like structures and centromeric asymmetry in the BrdU containing mouse chromosomes

Mouse cells cultured in the presence of BrdU or BrdC for one replication cycle were stained in a 4Na-EDTA Giemsa solution which stains BrdU-containing chromatin preferentially (Takayama and Tachibana, 1980). With this treatment clear bands (B-bands) were revealed along the length of the chromosomes. The B-banding patterns were identical with the G-banding patterns of this species except for the centromeric region in which lateral asymmetry of Giemsa staining was seen. The concomitant occurrence of the lateral asymmetry with the B-banding supports the assumption that the B-bands visualized by the present technique reflect the BrdU-rich chromatin regions differentially localized along the chromosomes. Most of the chromosomes constituting the mouse karyotype showed their own characteristic appearance of the asymmetry, but in some of them the asymmetry was not clear and the Y did not show any specific, centromeric staining. The marked coincidence of the B- and G-banding patterns seems to provide evidence for the involvement of AT-rich chromatin in the induction of positive G-bands. The present technique also seems quite useful to analyze chromosomes of some species in which ordinary G-banding techniques have been known to bring about only unsatisfactory results.