BrdU (green) localizes to only one of two nuclei (red) in a dividing neural stem cell.
According to the immortal strand hypothesis, which was first proposed in the mid-1970s, stem cells actively retain the oldest DNA during asymmetric cell divisions. That DNA should, statistically speaking, contain fewer replication-induced errors than DNA resulting from more rounds of replication. While tantalizing for its logic, the hypothesis has been controversial, and numerous studies have failed to find evidence for it.
Working with mouse neural stem cells, the authors labeled cells with BrdU and then looked at how the DNA segregated. When populations of cells were labeled, dispersed into single cells, and allowed to proliferate, they gave rise to neurospheres that frequently contained a few BrdU-labeled cells....
