Demonstration of chromosome replication by BrdU antibody technique and electron microscopy

We describe the use of different reporter groups in visualizing replication patterns on metaphase chromosomes after BrdU incorporation by the BrdU antibody technique for the electron microscope. There is an inverse correlation between the density of the label and the size of the reporter particles. This observation alludes to stereo problems interfering with the access of the labeled antibodies into the chromatin. The use of silver enhancement enables easy detection of 1-nm and 5-nm gold particles, which make replication patterns visible in the electron microscope as does the diaminobenzidine/H2O2 reaction. Possible consequences for the demonstration of replication patterns and for nonradioactive DNA in situ hybridization are discussed.