First-of-its-kind live imaging leads to major discovery in how cells
pattern in tissues
Movies in real time show cells of developing fruit fly eye move into
position

Date:
February 22, 2022
Source:
Northwestern University
Summary:
The ability of cells to self-organize into specific patterns in
tissues that serve a function is a universal feature of life. A
well-known and much studied pattern is the compound eye of the
fruit fly. Researchers now have discovered that the formation of
the pattern involves mechanical forces, not just chemical signals
transmitted between cells. Using first- of-its-kind live imaging,
the researchers saw cells moving into position as the eye develops;
the cells are not static as previously believed.



FULL STORY ==========================================================================
The ability of cells to self-organize into specific patterns in tissues
that serve a function is a universal feature of life. The stripes of a
zebra, our eyelashes, the spiral of seeds in a sunflower and the maze
patterns of snakeskins are just a few examples.


========================================================================== Another well-known and much studied pattern is the compound eye of
the fruit fly. This eye is a highly patterned hexagonal lattice of 800
clusters of photoreceptor cells. How does an amorphous blob of cells
develop into this precise and familiar pattern? Northwestern University researchers have discovered that the formation of the pattern involves mechanical forces, not just chemical signals transmitted between
cells.Using first-of-its-kind live imaging, the researchers saw cells
moving into position as the eye develops; the cells are not static as previously believed. This major discovery provides principles that should extend to other pattern systems.

"There is a constellation of patterns everywhere you look," said Richard Carthew, professor of molecular biosciences in the Weinberg College
of Arts and Sciences. "But there is no master artist. In this study we
are trying to understand how one pattern -- a pattern of great beauty
-- forms itself in the body.To our surprise, we found the cells are
pushed and pulled into position with certain rules, like a chess game."
The study will be published Feb. 22 in the online life sciences and
biomedicine journal eLife.

Carthew and Madhav Mani, assistant professor of engineering sciences
and applied mathematics at the McCormick School of Engineering, are co- corresponding authors of the paper. Kevin Gallagher, a Ph.D. student
in molecular biosciences and a member of Carthew's lab, is the paper's
first author.



========================================================================== "This work helps us better understand how life builds itself," said Mani,
a quantitative biologist. "The process is still mysterious. We study
the fruit fly eye because it is a model system and has been leveraged
to teach us a lot.

There are amazing engineering principles to learn from life. We
approached this study with an open mind and have learned something
new about self-assembly." "With our custom-built tools, we were able
to see something no one else has seen before -- a dynamic view of eye development," said Gallagher, also a quantitative biologist. "That the
cells were moving location was a complete surprise. What we saw didn't add
up to the historical paradigm. It's pretty crazy." The multidisciplinary
team used cutting-edge techniques developed by Gallagher to live-image
and analyze the dynamics of the eye's self-assembly. The researchers
identified the novel mechanical dynamics that, in concert with the
genetic and biochemical molecules, orchestrate the remarkable feat of bioengineering that the fly achieves.They also demonstrated that without
the correct mechanical forces, the eye does not self-assemble properly.

In addition to the live imaging, in which the eye was kept alive outside
the fly's body, the success of the study depended on a computational tool Gallagher built to identify and track every single cell. This enabled the researchers to see where each cell goes over a period of 10 hours.Within
a narrow zone, called the wavefront of patterning, there is a little
cascade of cells where cells are pushed, then stop and push other cells
into the right position, with the familiar hexagonal lattice emerging.

"Scientists have tried for 50 years to visualize the developing eye,"
said Carthew, an experimental biologist who has long studied fruit fly
eyes. "It's only by watching a movie in real time that you can understand
what occurs.

Kevin is the first person to achieve this." The research findings could
be used in bioengineering to make synthetic visual sensors, Carthew said,
in addition to helping scientists better understand how patterns form
in nature.

"If we ever hope to get to a point of being able to do 'true'
bioengineering, as we engineer with inert matter, then understanding
the connection between the mechanical and chemical principles in play
is a must," Mani said.

The research was supported by the National Institutes of Health (grant R35GM118144), the National Science Foundation (grant 1764421) and the
Simons Foundation (grant 597491).

========================================================================== Story Source: Materials provided by Northwestern_University. Original
written by Megan Fellman. Note: Content may be edited for style and
length.


========================================================================== Journal Reference:
1. Kevin D Gallagher, Madhav Mani, Richard W Carthew. Emergence of a
geometric pattern of cell fates from tissue-scale mechanics in
the Drosophila eye. eLife, 2022; 11 DOI: 10.7554/eLife.72806 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220222125055.htm

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