The emergence of a new skeletal element helped animals to reach land

The emergence of a new skeletal element helped animals to reach land
The emergence of a new skeletal element helped animals to reach land
Anonim

Scientists from the First Moscow State Medical University named after I. M. Sechenov and the Federal Research Center "Crystallography and Photonics" of the Russian Academy of Sciences, together with foreign colleagues, confirmed that the exit of sea animals on land was impossible without changing the structure of the skeleton. The most important role was played by the appearance of the bone pineal gland, a skeletal element that protects the cells of the growth plates from excessive stress. The results of the work were published in the eLife journal.

The growth of long bones in many animals is provided by growth plates - areas of cartilage tissue near each of the ends of the bone. Initially in the evolution of tetrapods of vertebrates, cartilaginous tissue is found at the ends of bones and serves for the growth and articulation of the skeleton. At some point in evolution, it divides into a growth plate and articular cartilage that covers the tip of the bone. Between them there is a bony epiphysis - a small bone, which gradually increases. By the time the growth of the organism stops, the growth plate disappears, and the pineal gland is connected to the main part of the bone. For a long time, scientists could not understand why it was necessary to separate the cartilage tissue into two similar structures. Earlier, an international team of scientists showed that the pineal gland stimulates the formation of a stem niche in the growth plate, in which conditions for self-renewal and multiple division of cartilaginous tissue cells are preserved. Researchers are now trying to understand when animals first developed this structure.

Evolutionary analysis showed that the pineal gland arose in higher vertebrates, which include reptiles, birds and mammals and their ancestors. These were the first organisms that began to spend their entire life on land, and scientists have suggested that the appearance of the pineal gland may be associated with a much greater mechanical load on the skeleton than in marine animals.

The authors compared several species in which the limbs are adapted to different loads. So, for example, bats from birth move with their mother, holding on to her, and the wings begin to be used only after a couple of weeks, and the secondary centers of ossification in the hind legs develop in them much earlier than in the wing bones. A similar dependence is observed in jerboas, which in the first two weeks crawl using only the front limbs, in the third week they begin to walk on all four legs, and only in the fourth week they begin to move on their hind legs. In cetaceans, which evolved from land animals, the secondary center of ossification, on the contrary, developed less and less and in some species it completely disappeared.

In addition, the author of the article showed that hypertrophied chondrocytes (cells of cartilage tissue, which are fundamentally important for bone growth) are most sensitive to stress, but in bones where there is ossification of the pineal gland, they can withstand much greater pressure. The findings can be useful in planning sports activities for adolescents and young people and in the development of new surgical methods for treating pineal gland injuries.

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