Understanding the mechanism that coordinates the regrowth of a complex structure such as a fin among the fish cells may help scientists understand the regeneration process in general, thus providing clues that will help in the development of clinical healing methods such as the regeneration of heart muscle cell tissue after a cardiac event
The tail fin of the zebrafish one day after its amputation (left side) and 10 days after the amputation (right side) - the tail fin has regenerated and grown again.
A lost tail fin can slow down the zebrafish a lot - at least for a week, until it grows a new fin. Now scientists have shown that they can "turn on" or "turn off" this regeneration mechanism in zebrafish with the flip of a molecular switch. Understanding the mechanism that coordinates the regrowth of a complex structure such as a fin among the fish cells may help scientists understand the regeneration process in general, thus providing clues that will help in the development of clinical healing methods such as, for example, the renewal of myocardial cell tissue after a cardiac event.
Regeneration is the ability of certain creatures to regrow complex body parts, tissues and whole organs after their amputation and even creating a whole organism from a certain organ or tissue. The meaning here is a perfect repetition both in terms of the structure and the function of the tissues. The phenomenon of regeneration is known mainly in plants, but this phenomenon also exists in animals, for example in amphibians. However, during evolution, the miraculous ability to regenerate gradually disappeared. In mammals, including humans, the ability to regenerate is extremely limited. In humans there are tissues that do not regenerate and in others there is a partial regeneration, a compensatory regeneration - a process of hypertrophy or hyperplasia that tries to compensate for the loss which includes two processes, the first is an attempt by the tissue to regenerate but together with this attempt the second process takes place which is the investment of fibrotic tissue in the places where the regeneration There was no integrity - creation of scar tissue.
The researchers claim that not only will their findings advance the research dealing with the regeneration of tissues and organs, but their findings can also lead to improved treatment methods in the field of bone marrow transplantation to restore the hematopoietic system in cancer patients.
The researchers' findings were published on 22.12.06 in the online journal Development ePress and in the journal Development. The principal investigator is a researcher on behalf of the Howard Hughes Medical Institute, Randall Moon, from the Stem Cell Institute of the University of Washington, and other central researchers are Christy Stoeck-Cooper and Gilbert Weinger, who designed and performed the experiments in Moon's laboratory.
The researchers used the regeneration of the caudal fin in the zebrafish as a model system. They discovered that there is a major cellular signaling pathway, called the Wnt/?-catenin pathway. This pathway is central to the activation of a very complex mechanism of organ regeneration. This pathway also plays a central role in the regulation of stem cells in the stages of embryonic development and in the maintenance of adult tissues. Failures in this pathway have been shown to lead to cancer as well as diseases related to bone density and neurodegenerative diseases.
The Wnt/?-catenin pathway consists of a large group of proteins that are activated when the Wnt signaling molecule binds to the receptors of the pathway found on the surface of the cell. This activation increases the levels of ?-catenin, which in its role is a super-regulator of multiple genes- which reaches the cell nucleus and there destroys them.
The researchers also found that another protein related to the Wnt protein, called wnt5b, inhibits regeneration. Wnt5b controls a signaling mechanism that is independent of ?-catenin-. Hence, Wnt proteins can activate more than one signaling pathway, and these pathways are involved in regeneration, but with opposite roles.
"In the past it was known that various components of the Wnt pathway were expressed during regeneration, but no one investigated in depth whether the pathways are indeed activated" says Moon. "And no one has differentiated between the two routes and tested the effects of each of them separately."
In their experiments, Stoeck-Cooper and Windinger genetically manipulated the Wnt/?-catenin pathway in fish and measured how much this manipulation affected the fish's ability to regrow a severed tail fin.
They used a fluorescent "reporter" gene, which revealed the activation of the Wnt/?-catenin pathway by glowing like a firefly. Using the reported gene, the researchers were able to show that the pathway was activated during regeneration, only in the area of the body where the regeneration occurred. Similarly, they saw that the pathway is activated during heart regeneration in zebrafish and mouse liver. In light of these findings, it is possible that the Wnt/?-catenin pathway functions in regeneration processes in different species of creatures and is a conserved mechanism in evolution. Later, the researchers found that the pathway is also activated during the creation of undifferentiated cells that thrived during tail fin cell regeneration.
The next step in the research was the creation of a genetically modified fish in which the Wnt/?-catenin pathway can be "turned off" by exposing the fish to hot water. When they did, the researchers found, regeneration was completely blocked. They were also able to increase the rate of regeneration by increasing the Wnt/?-catenin signal. The researchers emphasize that this finding is a significant finding regarding the cutting-edge research field of regenerative medicine, in which a means to encourage regeneration is a very valuable tool.
Conversely, when they genetically engineered a fish so that the wnt5b gene was activated in response to hot water, regeneration was delayed. The opposite is true in fish with a mutation in the wnt5b gene, where regeneration was found to be increased. This finding is expected, Moon says, since the loss of a functional inhibitor amounts to a double negative, meaning that regeneration will be accelerated.
"These experiments show that there is a new and completely unexpected mechanism that turns into the regeneration process" says Moon. "There have been other studies that have indicated that wnt5b-like genes can block the Wnt/?-catenin pathway, but none of them have tested whether this antagonism occurs in the context of the normal process of regeneration."
"Christie and Gilbert's experiments rigorously prove, through a genetic approach, that Wnt pathways are important and functional in the regeneration process" he says. "And even more, they show that in the study of injuries or inflammation in any context, the researchers must check whether Wnt signals are also involved in these processes. The experiments described here suggest that Wnt signaling is a universal component in regeneration pathways in animals."
According to Moon, Stoick-Cooper Weidinger's findings will have clinical implications regarding tissue regeneration, as well as encouraging stem cell growth. Stem cells are not mature cells, but cells that have not yet undergone differentiation and are capable of maturing and maturing into a wide variety of cell types.
"Wnt/?-catenin signaling plays an important positive role in the differentiation of cells and cells needed for regeneration" he says. "This corresponds to the findings of previous studies by our laboratory, in which we showed in animals that the activation of these pathways increases the success of transplants of hematopoietic stem cells from which the various blood cells are derived. Such implants in cancer patients, whose immune system has been destroyed by radiation or chemotherapy, are essential for healing; And sometimes they fail because the transplanted cells are not absorbed into the bone marrow. We believe that the amplification and strengthening of the Wnt/?-catenin pathway will increase the success rate of transplants of the hematopoietic stem cells in the bone marrow of the patients," he says.
In other clinical studies, Moon and his colleagues are testing whether the activation of the Wnt/?-catenin pathway can also increase the differentiation of embryonic stem cells into heart muscle cells, which can later be used in various heart diseases.
Moon and his colleagues are also investigating how the countless types of cells involved in the regenerative response respond to signals to activate Wnt and, in addition, how an injury manages to "turn on" the signaling of Wnt/?-catenin. The researchers believe that Wnt signaling will emerge as a therapeutic target in the field of regenerative medicine in the future.
For information on the website of the Howard Hughes Medical Institute
