Bromodeoxyuridine is a synthetic nucleoside that is an analog of thymidine. BrdU is commonly used in the detection of proliferating cellsin living tissues. 5-Bromodeoxycytidine is deaminated to form BrdU. BrdU can be incorporated into the newly synthesized DNA of replicating cells, substituting for thymidine during DNA replication. Antibodiesspecific for BrdU can then be used to detect the incorporated chemical, thus indicating cells that were actively replicating their DNA. Binding of the antibody requires denaturation of the DNA, usually by exposing the cells to acid or heat. BrdU can be passed to daughter cells upon replication. BrdU has been demonstrated to be detectable over two years post-infusion. Because BrdU can replace thymidine during DNA replication, it can cause mutations, and its use is therefore potentially a health hazard. However, because it is neither radioactive nor myelotoxic at labeling concentrations, it is widely preferred for in vivo studies of cancercell proliferation. However, at radiosensitizing concentrations, BrdU becomes myelosuppressive, thus limiting its use for radiosensitizing. BrdU differs from thymidine in that BrdU substitutes a bromineatom for thymidine's CH3 group. The Br substitution can be used in X-ray diffraction experiments in crystalscontaining either DNA or RNA. The Br atom acts as an anomalous scatterer and its larger size will affect the crystal's X-ray diffraction enough to detect isomorphous differences as well. Bromodeoxyuridine releases gene silenced by association with the histone caused by DNA methylation. BrdU can also be used to identify microorganisms that respond to specific carbon substrates in aquatic and soil environments. A carbon substrate added to incubations of environmental samples will cause the growth of microorganisms that can utilize that substrate. These microorganisms will then incorporate BrdU into their DNA as they grow. Community DNA can then be isolated and BrdU-labeled DNA purified using an immunocapture technique. Subsequent sequencing of the labeled DNA can then be used to identify the microbial taxa that participated in the degradation of the added carbon source. However, it is not certain whether all microbes present in an environmental sample can incorporate BrdU into their biomass during de novo DNA synthesis. Therefore, a group of microorganisms may respond to a carbon source but go undetected using this technique. Additionally, this technique is biased towards identifying microorganisms with A- and T-rich genomes.
