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Developmental biology - Evolutionary Genetics

Closing In On Organ Formation

Scientists clarify cell behavior driving left-right asymmetric organ formation...


Osaka University scientists using the fruit fly, Drosophila, are now able to clarify what cell behavior drives left to right asymmetry in organ development and placement.
Many organs initially arise from a simple sheet of cells which roll into a tube of cells. In continued development, these tubes bend and deform into a more complex final shape. This process was observed by researchers following the development of the hindgut of the model species: Drosophila, in its organ equivalent to our intestines.

In the Drosophila embryo, the hindgut first forms as a bilateral, symmetric tubal structure which rotates 90°counterclockwise (oriented from the insect's tail end) to become asymmetric. Before rotating, cells in the hindgut tilt left. This asymmetric movement is called 'chirality.'

Cell chirality disappears after the tubal rotation is complete, and had been thought only related to hindgut rotation. Previous studies, however, were only performed on preserved Drosophila specimens. So, the dynamic mechanism by which cell chirality is converted into a LEFT or RIGHT asymmetric roll prefacing organ formation, was never seen.

Now, researchers led by Kenji Matsuno PhD, Osaka University, use live images of the embryonic Drosophila hindgut roll, along with computer simulations identifying a new cell behavior called "cell sliding". This new movement assists in the Left/Right asymmetry in an organ.
"We found that when the hindgut rotates, the cells change position relative to the cells located below them by sliding left. We named this movement 'cell sliding.' In a mutant showing inverted cell chirality and hindgut rotation, cell sliding occurs in the opposite direction to that found in the wild or normal type. Thus, we confirmed that cell sliding is important for the LR hindgut asymmetric rotation."

Kenji Matsuno, Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Japan.

The research results are published in the journal eLife. These achievements deepen understanding of the mechanism behind the morphogenesis of organs that have tubular structures, such as the digestive tract and heart, and will be applicable to the regeneration of organs in the future.

Abstract
Polarized epithelial morphogenesis is an essential process in animal development. While this process is mostly attributed to directional cell intercalation, it can also be induced by other mechanisms. Using live-imaging analysis and a three-dimensional vertex model, we identified ‘cell sliding,’ a novel mechanism driving epithelial morphogenesis, in which cells directionally change their position relative to their subjacent (posterior) neighbors by sliding in one direction. In Drosophila embryonic hindgut, an initial left-right (LR) asymmetry of the cell shape (cell chirality in three dimensions), which occurs intrinsically before tissue deformation, is converted through LR asymmetric cell sliding into a directional axial twisting of the epithelial tube. In a Drosophila inversion mutant showing inverted cell chirality and hindgut rotation, cell sliding occurs in the opposite direction to that in wild-type. Unlike directional cell intercalation, cell sliding does not require junctional remodeling. Cell sliding may also be involved in other cases of LR-polarized epithelial morphogenesis.

Authors:Mikiko Inaki, Ryo Hatori, Naotaka Nakazawa, Takashi Okumura, Tomoki Ishibashi, Junichi Kikuta, Masaru Ishii, Kenji Matsuno and Hisao Honda.


Acknowledgements
Osaka University was founded in 1931 as one of the seven imperial universities of Japan and now has expanded to one of Japan's leading comprehensive universities. The University has now embarked on open research revolution from a position as Japan's most innovative university and among the most innovative institutions in the world according to Reuters 2015 Top 100 Innovative Universities and the Nature Index Innovation 2017. The university's ability to innovate from the stage of fundamental research through the creation of useful technology with economic impact stems from its broad disciplinary spectrum

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Jul 18, 2018   Fetal Timeline   Maternal Timeline   News   News Archive




Left-right (LR) asymmetric rotation and cell chirality in the Drosophila embryonic hindgut.
Image: Osaka University.


Phospholid by Wikipedia