Tuesday, December 13, 2011

DNA replication visualized in live organisms

When cells aim to grow and divide themselves, they need to replicate their DNA, so that a daughter cell also possesses a set of chromosomes, which serve as a blueprint for the cell. A new substance developed in Zurich, Swiss shows us which cells are actually replicating their DNA. It is the first time this process can be observed with our own eyes, in live organisms. This should aid in uncovering several problems in which cells have too much DNA replication, such as a virus infection or cancer.

The picture above shows what happens after the newly developed substance, dubbed F-ara-Edu, is injected into a zebrafish egg. Sites where DNA is replicated show up in green. It basically shows that large parts of the animal are undergoing DNA replication, which is not surprising for an organism that is still developing. More importantly, it shows we can finally see it happening, without having to kill the organism.

Building DNA
Green = DNA building blocks
F-ara-Edu makes use of the normal DNA replication system, by mimicking one of the building blocks present in our genetic code. It consists of four basic building blocks, that are abbreviated by their first letter: A, T, C and G. The dye mimicks the T, and is built in like a normal building block. After F-ara-Edu is incorporated in the newly built piece of DNA, scientists can detect it, and determine the rate at which new genetic code is made by looking at the strength of the signal. Their method has no notable side-effect on the organism, in this case a developing zebrafish, which is a big plus. Previous methods of detecting DNA synthesis stopped the whole process and caused cells, and consequently the organism, to die. While this does not always have to be bad in an experimental setup, these substances are of course not usable in human patients.

Use in the clinic
Visualizing cells that make new DNA is important in a number of situations. When cells are infected by viruses, the cellular machinery gets hijacked to produce viral DNA, which is consequently used to make more viruses. Therefore, a high F-ara-Edu signal could indicate virus infection when used in human patients. Additionally, cancer cells divide unusually fast, and therefore need a higher rate of DNA production. This would also be detectable by the dye.

F-ara-Edu provides a new way of uncovering viruses and cancerous cells, and could possibly serve as an early detection method, before any pathological symptoms are visible. Additionally, it can help scientists perform experiments. In a somewhat related experiment, scientists used glowing cats, to serve in HIV research. 

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