After introducing molecules of different colors in living cells, researchers at Cold Spring Harbor Laboratory were able for the first time to take movies showing how a gene can force a cell to make a protein. Genome News Network says this could help to discover why an anticancer drug works. The researchers think it would also help to design new drugs.
For the first time ever, researchers have captured on film how a gene goes about the business of directing a cell to make a protein.
Researchers at Cold Spring Harbor Laboratory in Cold Spring Harbor, New York, tagged different molecules different colors so they could see the process by which a living cell makes protein from DNA within its nucleus. The process is much more dynamic than they had imagined.
How did they perform this experiment?
David L. Spector and his colleagues designed a gene sequence that could be inserted into the human genome. Once there, it could be turned on, or activated, at will and the ensuing sequence of events could be directly visualized by labeling DNA, RNA, and protein different colors in living cells.
The movie first shows a tightly compacted region of DNA opening up as the gene is activated. RNA -- tagged yellow with a fluorescent protein -- appears first in the nucleus and then moves out to the cytoplasm, the region of the cell surrounding the nucleus. Ultimately, blue-colored protein appears in the cytoplasm in structures called peroxisomes.
This movie is available under the name "Visualizing the central dogma in living cells" from this page. But don't try it if you don't have a broadband connection: the file size is 11.8 MB for a duration of 7 seconds. Here is one shot from the movie. On the left part, here is the protein product encoded (in blue) (Credit: Spector Lab). You'll find more explanations on this page.
What can we expect from such a system?
Spector says his system can provide a direct view of gene expression and may help researchers understand what happens when things go wrong. He envisions inserting the easily visualized gene that he constructed into specific spots in the genome to get a clearer view of how genes are regulated in the context of a living cell.
"We might also use this system to see how small molecules such as anticancer drugs work in a living cell," says Spector. "We could get a direct view into whether a drug is shutting down gene activation or affecting the way RNA is processed. Ultimately this could help us do a better job at identifying and designing new drugs."
The research work has been published by Cell. Here is the abstract of this paper named "From silencing to gene expression: real-time analysis in single cells."
We have developed an inducible system to visualize gene expression at the levels of DNA, RNA and protein in living cells. The system is composed of a 200 copy transgene array integrated into a euchromatic region of chromosome 1 in human U2OS cells. The condensed array is heterochromatic as it is associated with HP1, histone H3 methylated at lysine 9, and several histone methyltransferases. Upon transcriptional induction, HP1alpha is depleted from the locus and the histone variant H3.3 is deposited suggesting that histone exchange is a mechanism through which heterochromatin is transformed into a transcriptionally active state. RNA levels at the transcription site increase immediately after the induction of transcription and the rate of synthesis slows over time. Using this system, we are able to correlate changes in chromatin structure with the progression of transcriptional activation allowing us to obtain a real-time integrative view of gene expression.
Sources: Nancy Touchette, Genome News Network, March 19, 2004; Cell, March 5, 2004
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