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Thursday, April 26, 2018

A new form of DNA in our cells

Por Jade

The double helix that contains the genetic instructions of all living organisms should perhaps incorporate a new structure that has been discovered in human cells. A team of Australian biologists has just discovered that the DNA of our cells is not only organized in the classical double-helical shape we all know.

On the contrary, other more complex structures that until now had only been manifested in laboratory samples, have been found for the first time in living cells, in a finding that could change cell biology forever. What are these new structures and what are they for? What effects do they have on the human body? Nobody knows for now. The study was just published in Nature Chemistry.

The discovery of what researchers describe as a "twisted knot" of DNA inside living cells confirms that the design of our genetic code is much more complex and intricate than previously thought. In the deepest part of the cells of our body lies our DNA. The information written in your code (about six billion letters A, C, G and T), provides precise instructions on how our bodies are built and how they work. Since the structure of DNA was discovered by Watson and Crick in 1953, the iconic shape of the "double helix" has captivated the imagination of the public.

But now we know that DNA can be organized, too, in completely different ways. Although we ignore the why and the function that these new and surprising structures could have. "When most of us talk about DNA," explains Daniel Christ of the Garvan Institute of Medical Research in Australia and co-author of the study, "we think of the double helix, but this new research reminds us that there are totally different DNA structures, which could be very important for our cells.”

The new DNA component identified by scientists is called "i-motif" and was discovered in the nineties, although so far it had only been seen in vitro and never in living cells. Now, thanks to the work of Christ and his team, we know that i-motif occurs naturally in human cells, which means that from now on researchers should pay close attention to this new structure and its role in biology of our cells. In the words of Marcel Dinger, another of the signatories of the article in Nature, "The i-motif is a 'node' of four-strand DNA. In the structure of the knot, the letters C (cytosine) of the same strand of DNA are joined together, which is very different from a double helix, where the 'letters' of opposite strands recognize each other, and where the C join to the G (guanines) ".

For the principal investigator, Mahdi Zeraati, the i-motif is, in addition, only one among an indeterminate number of structures that do not have the classical form of double helix and that also exist inside each of our cells. To carry out their study, Zeraati and his colleagues developed an antibody fragment (called iMab) capable of recognizing and specifically binding to the i-motifs. When this happened, its exact location was highlighted with a fluorescent green glow. "The most exciting thing," says Zeraati-, "is that we could see those green spots, the i-motifs, appearing and disappearing in the course of time, so we know that they are forming, dissolving and reforming."

Although there is still much to be learned about how this new structure works, researchers believe that transient i-motifs often form late in the life cycle of a cell, specifically in the phase called "late G1" when the DNA is " Read "more actively for your copy. The i-motif also tend to appear in the so-called "promoter regions" (areas of DNA that control whether genes are activated or deactivated) and in telomeres, genetic markers associated with aging. "We believe that the coming and going of the i-motifs is a clue to what they do," Zeraatti continues, "and it seems likely that they are there to help activate or deactivate genes, and to determine whether a gene is actively read or not."

"These alternative DNA conformations," concludes the researcher, "could be important for the cell's proteins to recognize their analog DNA sequence and exert their regulatory functions." Therefore, the formation of these structures could be very important for the cell function normally, and any aberration in these structures could have serious pathological consequences. "