The junction between the three cells acts as a gateway for the transport of substances

Epithelial cells that surround the developing egg cells in the Drosophila ovary. Scientists examined the ovaries in tissue culture using a confocal fluorescence microscope. They found that at the point where the membranes of the three cells (pink) meet each other, the cells regularly loosen connections and the yolk-forming protein is transported to the egg through the intercellular space (green). Credits: Isasti-Sanchez et al./Dev Cell 2021

In multicellular organisms, cells build connections with each other, covering the surfaces of tissues and organs and forming cell layers that separate structures within the body. For example, the skin forms a mantle around the entire organism, and the layers of cells that line blood vessels form a boundary between blood flow and tissue.

Due to the special connections between adjacent cells, these cell barriers, on the one hand, are stable and firmly anchored, protecting the body and organs from pathogens, but on the other hand, permeating certain substances and migrating cells. Maintain sex. This is a way for cells to transport dissolved nutrients to organs, a way for cells of the immune system to move from the blood across the walls of blood vessels to inflamed tissue.

Scientists at the University of Münster have investigated an equivalent process in the ovaries of fruit flies (Drosophila melanogaster). Here, the mature egg cell is surrounded by a layer of epithelial cells in which the egg absorbs the yolk-forming protein. At the point where the three cells meet, researchers have found that epithelial cells loosen their connections in a controlled manner and that the yolk protein is transported to the egg cell through the resulting gap.

Where only two cells connect, the connection is maintained and the integrity of the organization is not compromised. “Our findings contribute to a better understanding of how cell barriers function and are reconstructed during development, and provide the basis for deciphering the mechanisms of specific pathological processes. “More,” explains Dr. Stephen Ruschnig, a developmental biologist and research project leader. This study is currently published in a scientific journal.Developing cells“.

Survey of fruit fly egg development

Whenever a substance is transported through a cell layer, the cell absorbs them through the membrane on one side of the cell layer and then releases them on the other side-it requires a lot of energy-or the substance. Spreads through the gaps between cells. Studies of other insects have already shown that yolk proteins are usually transported to the egg cell through the space between the epithelial cells that surround the egg. A new study confirms that this also applies to fruit flies. However, it was not previously clear how cells could temporarily open intercellular spaces while keeping tissue intact.

To visualize these cellular processes and analyze the molecular mechanisms behind them, scientists genetically label specific proteins in the fly with fluorescent molecules, keep the ovaries in tissue culture, and confocal laser scanning microscopy. The living tissue was examined using. They turned their attention to proteins on the surface of epithelial cells. These so-called adhesive proteins mechanically organize the cell network and seal the space between cells.

The cell barrier opens at the junction of the three cells

Scientists have discovered that epithelial cells sequentially remove four different adhesive proteins from the membrane. “This process takes hours, and cell connections only open when the last protein is gone,” said the first author of the study and a candidate for a doctoral program in the Integrated Research Training Group of the Collaborative Research Group. Biologist Jone Isasti-Sanchez explains. Research Center, University of Münster 1348 “Dynamic Cell Interface”. After the junction opens, the uptake of yolk protein into the egg proceeds for about 16 hours, after which the process is reversed and the intercellular space closes again.

Researchers have demonstrated that cells open contact sites by incorporating adherent proteins from the surface into the cells using a basic cellular process called endocytosis. An important new finding is that endocytosis appears to occur more often at the points where the three cells meet, and as a result, cell connections open only at these points. Contact is maintained if only two cells meet. “The fact that this process occurs selectively at the contact points of the three cells, and in such an orderly manner, is probably important to prevent tissue collapse,” says Stefan Luschnig. In addition, he adds, the process probably needs to be done in a very controlled manner, as opening the gates in the tissue risks the invasion of pathogens.

In their experiments, scientists can also show that the amount of the adhesive protein E-cadherin is genetically increased or decreased, and that the amount of this protein determines how wide the intercellular space opens. I did. In addition, they found that the mechanical tension of the cytoskeleton plays an important role in the process. This tension is created by a structure consisting of the proteins actin and myosin, which, like rubber bands, can surround and contract cells. When researchers increased the activity of intracellular myosin, the cytoskeleton contracted further, preventing cell connections from opening.

Decode: Barrier structure between 3 cells

For more information:
Jone Isasti-Sanchez et al, a temporary opening at the apex of three cells, regulates paracellular transport through the follicular epithelium during Drosophila oogenesis. Developing cells (2021). DOI: 10.1016 / j.devcel.2021.03.021

Provided by Münster University

Quote: The junction between the three cells is the transport of material obtained from on April 7, 2021 (2021, 4). It functions as a gateway for (7th of April).

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The junction between the three cells acts as a gateway for the transport of substances

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