Thursday, December 22, 2011

Genetic material in cells contains self-destruct timer

Cells from basically all life forms possess DNA, which is the blueprint for all material required to build cellular structures and maintain its processes. DNA is turned into proteins via intermediates called mRNAs. These molecules are read-outs from their respective genes, and function as the code that is being read by specialized structures that make the protein. But after a while, the cell has made enough protein and the mRNA needs to be destroyed. Scientists from the Albert Einstein College of Medicine found that mRNA molecules are born with a self-destruct timer, which shows how our cells regulate one of its most important processes.

Cell cycle
To study the timely effect of mRNA present in the cell, the researchers studied the cell cycle in yeast. This particular cycle governs the birth of daughter cells: creating new cells is performed by splitting a cell in two, each one receiving its own set of DNA and cellular machinery, so it may work on its own. Numerous proteins are involved with the cell cycle, and because there is a number of sequential steps, it requires closely regulated numbers of proteins, and thus closely regulated numbers of mRNA, that serves as the blueprint. The scientists found two genes that possess a timer that determines their life span, thereby showing that their time inside the cell is already determined at birth. 
First, the cell grows and DNA is replicated. Then the chromosomes are divided and the cell branches off.
Time bomb
The two genes play an important role in the cell cycle, and carry, next to genetic code, a protein which serves as a ticking bomb. During mRNA formation of the two investigated genes, this particular protein is added, and is activated once it is shipped to the area where the mRNA is being translated into protein. That gives the local machinery a limited amount of time to create protein, which is just about right for what the cell needs. The image below shows the effect inside the cell. The red dots, which indicate mRNA appearing during cell division, but after both cells have branched off from each other, readily disappear again.
Reading DNA and creating transcripts to serve as a blueprint in protein formation is one of the most fundamental and important processes of the cell, and thus life. If we learn how the body controls mRNA, we learn the basics of how a cell is maintained. This is important for various reasons. Naturally, we are keen to discover the fundamental principles of life, but our understanding can also lead to new therapies when things go wrong. In cancer for example, certain genes are expressed too often, while others are inhibited. Because DNA transcription governs the production basically everything inside the cell, its behaviour can be severely altered. In most cases, the cell simply dies from failure of maintaining itself, but ever so often, a cell achieves uncontrolled growth which leads to a tumour. Of course, before we can use this in therapies, scientists will have to proof that the same mechanism applies for human cells, and that many more genes work with time bombs. But because this is such a fundamentally important mechanism, it is likely we will find the same thing in human cells. 

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