Great mechanism: Sea squirts use frictional forces for embryonic development
Shortly after fertilization, the animal egg cell begins to reorganize itself. But how does it work? Mechanical effects appear to be involved.
© Velvetfish / Getty Images / iStock (details)
Sea squirts are the invertebrates most closely related to vertebrates.
Anyone who has made pottery knows how clay can be shaped into all kinds of shapes using only the friction between the hands. Sea squirt eggs use a similar principle when they reorganize themselves after fertilization. Friction between components within the cell causes shape changes that lead to its development. This is what a European research team showed in a study, Which was published in the specialized journal “Nature Physics”..
Sea squirts, also known technically as ascidians, are sessile tunicates that inhabit oceans throughout the world from the shelf to the deep sea. Some species can also be found in German marine waters. At first glance, when fully grown, they look like rubbery lumps, but they are considered the closest living relatives of vertebrates, including humans. In particular, their tadpole-like larvae show close similarities to vertebrate embryos in some organs and tissues. For this reason, they are often used in basic research as a model organism to study early embryonic development. Almost all sea squirts are hermaphrodites, meaning they produce both male and female gametes.
After successful fertilization by male sperm, animal egg cells normally undergo cytoplasmic restructuring, during which the cell contents and components change. This process greatly shapes the subsequent development of the fetus. In compression, this remodeling results in the formation of a bell-like protrusion known as the contraction pole. Important substances accumulate there that enhance the maturation of the fetus. But exactly how this bump occurs has not yet been clear.
Myoplasm has a bigger role than thought
Under the microscope, the research group led by first author Silvia Caballero-Mancebo from the Institute of Science and Technology in Austria found that the cellular changes that lead to the formation of the contraction pole come from the actin-myosin cortex – a dynamic structure found in animal cells located near the cell membrane. “Our research has shown that the actin and myosin cortex contracts and moves after fertilization. This leads to the first changes in cell shape,” explains Caballero-Mancebo According to a press release issued by her institute. However, this alone does not seem to explain the entire process.
By taking a closer look at the myoplasm — an area of cytoplasm in fertilized sea squirt eggs from which the larval tail muscle cells arise — the scientists were able to observe more details. During the movement of the actin-myosin cortex, the myoplasm folds and forms numerous bulges due to the frictional forces that arise between the two components. When the process stops, the frictional forces disappear and the myoplasm bulges become a bell-shaped protrusion.
The study thus highlights the importance of frictional forces in shaping and shaping the developing organism. Carl Philipp Heisenberg, professor of evolutionary biology and chief scientist at ISTA, said he would like to try to learn more about the myoplasm in the future. “Researching their unusual material properties and thus understanding how they may be involved in the design of sea fountains will be particularly exciting in the future.”
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