How do blood vessels come into the world? The institute’s scientists have revealed surprising findings following observations of fins of young zebrafish
In some cultures, the family you were born into largely determines your future. Scientists at the Weizmann Institute of Science have recently revealed that the family lineage has special weight even when it comes to our blood vessels. “We discovered that in order to perform special functions properly, blood vessels need to be born to the right parents – they seem to ‘remember’ where they came from,” says research team leader Prof. Karina Yaniv of the Department of Immunology and Biological Regeneration at the Weizmann Institute of Science. These groundbreaking findings are published today in the scientific journal Nature, Revealed following observations of vascular development in a unique organ: the fins of young zebrafish.
Blood vessels are the tubes that serve all the cells and tissues and reach every point in our body. Although they are the same transport system, the structure and function of the blood vessels in different organs differ significantly from each other. For example, while the cells of the blood vessels in the kidneys are perforated, to allow filtration and passage of various substances, and these health are adapted to gas exchange – the walls of the blood vessels in the brain are almost completely sealed (a phenomenon known as “blood-brain barrier”), to protect the brain Against unwanted effects.
Despite the enormous importance of the circulatory system in health and disease conditions, the way in which these differences are created between the various blood vessels is not sufficiently understood. What is apparently known is that blood vessels grow in one of two ways: they branch from existing blood vessels or are formed “out of nothing” from stem cells that mature and differentiate into cells that make up the walls of blood vessels. However, in the new study, the scientists, led by Dr. Rodra Nayan Des from Prof. Yaniv’s laboratory, discovered that blood vessels can be formed in another and particularly surprising way: by converting lymph vessels into blood vessels. Fluorescence, which allowed the development of lymph and blood vessels in the fin.At the follow-up, the researchers noticed that lymph vessels, belonging to the body’s immune system, were the first to appear in this bone organ – even before the appearance of bone tissue; To blood vessels.
How can the so-called wasteful and unusual choice be explained? On the face of it, it would have been much simpler and more economical if the blood vessels in the fin were formed by branching from larger blood vessels that already exist nearby. To solve the mystery, the researchers tracked engineered fish, which are unable to produce lymph vessels at all. They found that in the absence of these, the blood vessels in the fin did branch off from nearby blood vessels, but the fish’s navigational organ grew defective – its bones were deformed and it was characterized by several foci of internal bleeding. Moreover, when the researchers compared the function of the blood vessels in normal fins to the defective fins, they found that in the damaged fins the blood vessels, formed from larger blood vessels, flowed large amounts of red blood cells into the developing organ, while in fins that developed normally, the blood vessels Converted from lymph vessels, flowed red blood cells in a moderate and controlled manner.
The researchers speculate that the relatively small amount of red blood cells in the normal fins ensures an oxygen-poor environment – an important condition for the normal development of bone tissue; In contrast, an excess of red blood cells in the engineered fish did not allow for oxygen-poor conditions, and this was probably due to the defects observed in the experiment. In other words, only the blood vessels with the correct family pedigree suited the unique task: the proper development of the fin that is an important part of the fish’s movement and navigation system.
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The miraculous ability of zebrafish to regrow organs has also allowed researchers to examine what happens to adult fish after fin injury. They saw that the same process they identified in young fish was repeated even when the organ regenerated in adult fish: first lymph vessels appeared and later they became blood vessels.
“It has been known in the past that blood vessels can grow lymph vessels, but in the study we showed for the first time that the reverse process can also take place, as part of normal development,” says Dr. Des. For the function required of them. “
The findings of the study may be relevant not only to fish but also to other vertebrates, including humans. “So far, everything we have discovered about fish has been found to be true in mammals as well,” Prof. Yaniv emphasizes, adding: The cell is shaped not only by the place of ‘residence’, that is, the type of signals it receives from the nearby tissue, but also by the identity of its parents. “
The new discoveries open up a variety of new research directions in medicine and the study of fetal development. For example, future medicine is expected to rely on tissue engineering and organ transplantation, and mapping the pedigree of the blood vessels may prove essential if we want to provide each tissue and organ with the type of blood vessels they need. Also, a better understanding of the differences in blood vessel formation may contribute to the fight against common diseases: if we identify the unique characteristics of coronary blood vessels in the heart, we may be able to prevent or treat heart attacks more easily; In addition, we may be able to develop new therapies that will disrupt the blood supply to cancerous tumors or learn how to bypass the blood-brain barrier to lead drugs more effectively to this important organ.
Because her laboratory specializes in lymphatic vessel research, Prof. Yaniv is particularly pleased with the new discovery: “It is customary to refer to lymphatic vessels as the ‘poor relatives’ of blood vessels, but perhaps the opposite is true, sometimes they are the firstborn.”
Yaara Tevet, Stav Spriel, Noga Moshe, Josephina Lambiasa, Dr. Ivan Bassi, Dr. Julian Nissenbaum and Dr. Roi Avraham from the Institute’s Department of Immunology and Biological Regeneration participated in the study; Dr. Yanchou Han and Prof. Kenneth Foss From Duke University School of Medicine; Matthias Bruckner and Prof. Vivka Herzog of Erlangen-Nuremberg University and the Max Planck Institute for Molecular Biomedicine; And Dana Hirsch Dr. Raya Eilam of the Institute’s Veterinary Resources Department.
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