Professor Peter Gograten from Connecticut and his Israeli colleague Dr. Uri Gofna reveal a stormy genetic dialogue between different biological species and threaten the conventional genetic tree structure
Since the days of Charles Darwin, it has been customary for the scientists dealing with evolution to describe the development of the different biological species - unicellular and multicellular, plants and animals - in the form of a tree. At the base of the trunk of this tree stands the first living cell, it is the "common ancestor" of all living things. During evolution, when one biological species splits into two species, such as humans and chimpanzees, it is commonly described as two branches sprouting from a common branch. The key point in this model is that the two sexes, like the two branches, do not meet again. Each biological species continues its independent evolutionary development, does not go back down the tree and does not make contact with other branches. Two species that have separated from each other do not come back together and do not exchange changed genes between them - each has its own path of genetic change and evolution.
But Professor Peter Gugraten, head of the department of molecular cell biology at the University of Connecticut and Dr. Uri Gofna, a senior lecturer in the department of molecular microbiology at Tel Aviv University, claim otherwise. In their joint and separate studies, they present cases of gene transfer between different and separate biological species, a mechanism known in their words as "horizontal gene transfer". Gugraten, Gofna and their colleagues are therefore reshaping the familiar and well-known evolutionary path: no longer an evolutionary tree but an evolutionary network in which there are horizontal connections between the various branches. Another pictorial image used by the two is a potato. The "potato" is the common body with a large volume where lateral gene transfer can take place, and from which multiple and different sprouts emerge - evolutionary branches with a more classical structure.
Among ancient animals, such as single-celled prokaryotic organisms, found at the heart of the "potato", horizontal gene transfer is common as a daily occurrence. However, it was found that such gene transfer also takes place between more developed organisms. Different yeast cells, for example, exchange these genes with each other. Certain bacteria can insert genes into plant cells and thus cause the formation of nodules, growths that provide them with nutrients and a niche for life.
The research way to prove lateral gene transfer is to find identical genes in two organisms belonging to different biological species. And this is not as rare as one might think at first. But Gugraten and Gupna are trying to decipher mechanisms that allow lateral gene transfer. Heredity throughout the generations explains very well the transfer of genes between creatures and their offspring, from a bacterium that splits into two to a cow giving birth to her calf, while the transfer of genes between different creatures must be aided by an agent, a "messenger to speak transgression" who will transfer genes between different species.
Among bacteria, these messengers are often viruses (viruses, or phages) known as bacteriophages. When such a virus attacks a bacterium, it inserts its genes into the drum of the bacterial cell body and forces the bacterium's cellular machinery to produce the DNA or RNA of the virus, wrap it in a viral protein and create many copies of the bacteriophage. During this process, a segment of the bacterial nucleic acid (DNA or RNA) is sometimes trapped inside the bacteriophage's nucleic acid. The next generation of the bacteriophage therefore contains bacterial genetic material, and when the copies of the virus penetrate new bacteria, they inject the nucleic acid segment of the previous bacteria along with their genetic information. If the bacteriophage infects a bacterium of another species, it therefore transfers genes across the genetic tree. And if the genetic segment contains genes that give the new bacterium an advantage, such as resistance to antibiotics, a bacterium that is more adapted to its environment is created in this way, in a way that is not possible with normal inheritance. Transverse gene transfer is therefore a very effective mechanism that allows evolutionary "shortcuts" and even "jumps", and understanding it is very important in understanding how viruses and bacteria work.
Insertion of foreign genes into the bacterial genetic information can be done using several enzymes. One of these enzymes is called "homing endonuclease" and its function is to cut the bacterial nucleic acid at a specific point near which the foreign gene will invade the bacterium's genome. These enzymes are also found in "halophilic" (literally: salt-loving) bacteria species from the archaea kingdom, which are able to live at a very high level of salinity, even in the waters of our Dead Sea, mistakenly called the "Death Sea". Gofna and Gugraten focus on these bacteria with the aim of deciphering the molecular mechanism of lateral gene transfer. (By coincidence, the deciphering of the molecular structure of the ribosome, which earned Professor Ada Yonet the Nobel Prize in Chemistry, was carried out, among other things, in such halophilic bacteria.)
Do other organisms exchange genes in a mechanism of lateral gene transfer with biological species other than viruses and bacteria? It is accepted by scientists that the origin of intact subcellular organelles, such as the mitochondria, is in bacteria from the bacterial kingdom that merged with bacteria from the archaea kingdom and created the first eukaryotes.
We humans see ourselves at the top of the evolutionary tree, and are always interested in the practical implications of scientific research. Does research in the field of lateral gene transfer between unicellular organisms have any application to help complex creatures like humans? Gofna and Gugraten, like all scientists engaged in pure research, smile at this common question, and their first answer is that the motivation for their research is pure scientific curiosity and not necessarily practical possibilities for their results. However, there is no doubt that the mechanisms of transfer of hereditary information between different species have many practical consequences, since man today is the number one agent of transferring genes from production to production in the genetic engineering processes. Mice that glow with the greenish light of jellyfish, or rats whose actions can be controlled using a light-sensitive gene derived from algae are examples of artificial gene transfer. The results of Gugraten and Gofna's research and understanding the mechanisms of "natural genetic engineering" can indeed contribute, according to them, for example in the field of gene transplantation for medical purposes (Gene Therapy).
Professor Gugraten, was born in Germany and now lives and works in the United States. He came to Israel as part of the American Fulbright program for the exchange of lecturers and students. Israel's participation in this program is managed by the US-Israel Education Foundation. Professor Gugraten's visit to Tel Aviv University as a Fulbright Fellow was made possible thanks to additional funding received from the Edmond Safra Program for Bioinformatics.
In response to my question as to why he chose to come to Israel, Professor Gograten explains that Israeli researchers are leading in the field of bioinformatics research in general and in topics close to his heart and his own research in particular. And he says that in his research experience, Israeli scientists are characterized by openness and a desire for scientific cooperation. These reasons, combined with the fact that Israel is an interesting country, brought him into contact with Dr. Uri Gofna. Uri Gofna is a graduate of the Technion in Biotechnology who completed his second and third degrees at Tel Aviv University and returned to this university at the end of post-doctoral research at Dalhousie University in Nova Scotia.
Will the collaboration between the two lead to rewriting the evolution textbooks? time will tell.
Dr. Deborah Jacobi is a member of the educational staff of Hamada, the center for scientific education in Tel Aviv, and a scientific editor at Scientific American Israel.
