A new study reveals that ascidian oocytes undergo post-conception developmental changes using internal friction, drawing an interesting parallel to how a potter shapes clay. The sea squirt, or ascidian, serves as an important model for understanding vertebrate development and shares similarities with humans. Credit: SciTechDaily.com
Scientists are investigating how frictional forces drive the development of marine life.
When a potter spins a spinning wheel, the friction between his hands and the soft clay allows him to shape the clay into all kinds of shapes and creations. An interesting parallel is that ascidian oocytes (immature egg cells) use friction within various internal compartments to undergo developmental changes after conception. Research by the Heisenberg Group at the Austrian Institute of Science and Technology (ISTA) natural physicsSo let me explain how this works.
![coral reef squirt](https://scitechdaily.com/images/Sea-Squirts-on-Reef-777x518.jpg)
A sea squirt attached to a coral reef. Marine organisms are excellent models for studying vertebrate developmental processes.
Diverse marine life: the world of sea squirts
The sea is full of fascinating creatures. From algae and brightly colored fish to snails and sea squirts, there’s a whole different world underwater. In particular, sea squirts and sea squirts are extremely rare. After a freely moving larval stage, the larva lands and attaches to a solid surface, such as a rock or coral, and develops its characteristic tube (siphon). Although they look like rubbery blobs as adults, they are our closest invertebrate relatives. Especially in the larval stage, sea squirts are surprisingly similar to us.
Therefore, ascidians are often used as a model organism to study early embryonic development in ascidians. vertebrate What humans belong to. “Ascidians exhibit basic developmental and morphological characteristics of vertebrates, but also possess cellular and genomic simplicity typical of ascidians. invertebrates” explains Professor Carl Philipp Heisenberg of the Austrian Institute for Science and Technology (ISTA). “The ascidian larva, in particular, is an ideal model for understanding early vertebrate development.”
The researchers labeled actin proteins in the actomyosin cortex (left, green staining) and the sarcoplasm (right, blue staining) to visualize the post-fertilization movement of the oocyte. As the actomyosin cortex moves in the lower region of the egg, it mechanically interacts with the sarcoplasm, causing the sarcoplasm to buckle. The buckle will eventually be disassembled into a retractable pole. Credit: © Caballero-Mancebo et al./Nature Physics
The latest research from his research group is natural physicsprovides new insights into its development. The results of this study suggest that during fertilization of ascidian oocytes, frictional forces play an important role in the internal remodeling and reorganization of ascidian oocytes, heralding the next step in the developmental cascade. ing.
Decoding oocyte transformation
Oocytes are female reproductive cells involved in reproduction. After successful fertilization with male sperm, animal oocytes typically undergo cytoplasmic rearrangements that change their cellular contents and components. This process establishes the blueprint for the embryo’s subsequent development. In ascidians, for example, this swapping results in the formation of a bell-like protrusion (a small ridge or snout) known as the contractile pole (CP), which collects essential substances that promote embryonic maturation. However, the underlying mechanisms driving this process are unknown.
Formation of contractile poles. Microscopic time-lapse of cell shape changes in ascidian oocytes after fertilization: from unfertilized egg to contractile pole initiation, contractile pole formation, and contractile pole resorption. Credit: ©Caballero-Mancebo et al./Nature Physics
A group of scientists from ISTA, the University of Paris, CNRS, King’s College London, and Sorbonne University set out to solve the mystery. For this effort, the Heisenberg Group imported adult sea squirts from Roscoff Marine Station in France. Almost all sea squirts are hermaphrodites, as they produce both male and female reproductive cells. “In the lab, we store it in salt water tanks. seed“A suitable method to obtain eggs and sperm to study early embryonic development,” said Silvia Caballero Mancebo, first author of the study and a former doctoral student in Heisenberg’s lab. says.
![Formation of contractile poles](https://scitechdaily.com/images/Formation-of-Contraction-Pole-777x188.jpg)
Formation of contractile poles. Microscopic time-lapse of cell shape changes in ascidian oocytes after fertilization: from unfertilized egg (1st image from the left) to contraction pole initiation (2nd and 3rd images from the left) to contraction pole formation (4th image from the left) . Credit: © Caballero-Mancebo et al/natural physics
The researchers analyzed fertilized ascidian oocytes under a microscope and noticed that they followed highly reproducible changes in cell shape that led to the formation of contractile poles. The researchers’ initial work focused on the actomyosin cortex, a dynamic structure found beneath the plasma membrane of animal cells. It is composed of actin filaments and motor proteins and generally acts as a driver of cell shape changes.
“We found that when a cell is fertilized, the increased tension in the actomyosin cortex causes the cortex to contract, creating movement (flow) and resulting in an initial change in the shape of the cell,” continued Professor Caballero-Mancebo. Ta. However, actomyosin flow ceased during expansion of the contractile pole, suggesting that there are other participants involved in this prominence.
![Silvia Caballero Mancebo](https://scitechdaily.com/images/Silvia-Caballero-Mancebo-777x518.jpg)
Silvia Caballero-Mancebo. ISTA graduates find great joy in solving nature’s puzzles and turning them into stories. Credit: © Nadine Poncioni/ISTA
Frictional forces influence cell reformation
The scientists took a closer look at other cellular components that may play a role in expanding the contractile pole. In doing so, they study the myometrium, a layer of intracellular organelles and molecules located in the lower region of the ascidian egg cell (a morphology associated with many vertebrate and invertebrate eggs is found). I encountered quality. “This particular layer behaves like a stretchable solid, changing its shape along with the oocyte during fertilization,” Caballero-Mancebo explains.
![carl philip heisenberg](https://scitechdaily.com/images/Carl-Philipp-Heisenberg-777x999.jpg)
Carl Philipp Heisenberg of the Austrian Institute of Science and Technology (ISTA). ISTA’s research group of cell biologists studies sea squirts and zebrafish to understand how unstructured cell clumps transform into elaborate shapes during development. Credit: © Nadine Poncioni/ISTA
During actomyosin cortical flow, the sarcoplasm folds and forms many buckles due to the frictional forces established between the two components. When actomyosin stops moving, the frictional force also disappears. “This arrest causes multiple sarcoplasmic buckles to resolve into distinct bell-shaped ridges, ultimately leading to the expansion of the contractile pole,” Caballero-Mancebo added.
This study provides new insights into how mechanical forces determine the shape of cells and organisms. This shows that frictional forces are crucial for the formation and formation of evolving organisms. However, scientists are just beginning to understand the specific role of friction in embryonic development. Mr. Heisenberg added: “The sarcoplasm is of great interest because it is also involved in other embryonic developmental processes in ascidians. We wanted to investigate its unusual material properties and understand what role they play in ascidian formation.” will be very interesting.”
Reference: “Frictional forces determining cytoplasmic reorganization and shape changes in ascidian oocytes during fertilization” Silvia Caballero-Mancebo, Rushikesh Shinde, Madison Bolger-Munro, Matilda Peruzzo, Gregory Szep, Irene Steccari, David Labrousse-Arias , Vanessa Zheden, Jack Merrin, Andrew Curran Jones, Raphael Voiturier, Carl Philip Heisenberg, January 9, 2024, natural physics.
DOI: 10.1038/s41567-023-02302-1