Laser in cytometry: Applications in flow cytogenetics

Denaturation behaviour of DNA-protein-complexes detected in situ in metaphase chromosomes in suspension by Hoechst 33258 fluorescence

The denaturation behaviour of DNA-protein complexes in metaphase chromosomes in suspension was analysed in situ by Hoechst 33258 fluorescence. The results indicate that due to the stability of the dye molecule and the product of the molecular extinction coefficient and the quantum yield at different temperatures, Hoechst 33258 is a suitable probe for the detection of double-stranded DNA. Thus, it is possible to monitor the concentration of double-stranded DNA in a suspension by measuring the total fluorescence intensity. The fluorescence denaturation profiles of DNA (calf thymus) were found to be comparable to absorption measurements. The decrease in fluorescence of metaphase chromosomes in suspension with increasing temperature may therefore be used to detect conformational changes of DNA in situ.

Determination of the electrophoretic mobility of chromosomes by free flow electrophoresis. I. Morphology and stability

Isolated metaphase chromosomes of several fibroblastoid cell lines (Chinese hamster, Chinese hamster x human hybrid) were subjected to free flow electrophoresis (FFE) to study their electrophoretic mobility (EM). The morphology and stability of the chromosomes were unaffected by FFE as examined by cytogenetic methods and flow cytometry. The chromosomes of the complement all showed similar EM under most of the conditions applied. At neutral pH the EM of the chromosomes had the same sign as free DNA and about 2/3 of its magnitude. The variation of EM with buffer parameters such as ionic strength, valence of counterions, buffer capacity and dielectric constant of the solvent were investigated. Thermal denaturation increased the EM of the chromosomes by 20%. Partial denaturation might offer a possibility to separate or enrich large amounts of chromosomes by FFE.