Folding, Unfolding, and Folding Again: The Complex Task of the "Simplest Animal"

"No brain," "no muscles," "no mouth or stomach"—such creatures fold and unfold their bodies like origami to create three-dimensional shapes. At Stanford University's Prakash Lab, researchers have discovered a type of "tissue folding" in one of the simplest animals, the placozoan Trichoplax adhaerens (hereafter referred to as Trichoplax), which has not been reported in nature before.Phys.org

The significance of a 1mm "flat animal" transforming into a three-dimensional shape

Trichoplax is a translucent animal approximately 1mm in diameter, consisting of two layers of epithelium and an intermediate layer, lacking neurons and muscles. Despite this, it exhibits surprising behaviors such as "hunting" algae for food and defending against predators with toxins, capturing the interest of researchers.BioInteractive

Until now, Trichoplax has often been described as a "2D moving flat organism." However, this study overturns that "premise." Trichoplax can fold its body and take on a 3D shape depending on the situation. Moreover, the way it folds is not fixed to one type but is **non-stereotyped** and diverse.Dryad

Cilia: More than just "hairs that move water"

The key point is the cilia growing on the cell surface. Cilia are often associated with transporting mucus in airways or allowing microorganisms to swim in water, giving the impression of being "organs for fluid." However, the research team demonstrated that the cilia of Trichoplax move as if "walking" on the surface, shaping the tissue. Phys.org

In fact, the concept of "moving on surfaces (walking/crawling)" with cilia, aside from "swimming with cilia," is known in biological contexts. There are also overviews that mention Trichoplax using cilia for "walking" on surfaces.OUP Academic

However, the novelty of this study lies in the fact that this walking is not just for movement but serves as the driving force for "folding and unfolding epithelial sheets", transforming their morphology.Life Science Network

Folds arise from "environment and movement," not "planning"

In textbooks on embryonic development, epithelial folding is often portrayed as following a "stereotyped procedure (pathway)" through changes in cell shape, proliferation, and molecular signaling. However, in this study, the folding/unfolding of Trichoplax does not follow a clear "folding → next here →…" linear path.
The research team organizes that the "transition" between folded and unfolded states arises as a result of **environment (substrate shape) and movement (motility)**, influenced by the adhesion of cilia to the substrate (floor) and the dynamics generated by ciliary walking.Dryad

This is also why it is said to be "like origami." Origami is determined by the constraints of "foldability" inherent in the paper and the folding lines and surrounding conditions (how it is pressed and supported). Similarly, the physics of epithelial sheets as thin sheets is effective. This study is a striking example of utilizing that physics without a nervous system.Phys.org

Tracking "folding" and "unfolding" with 4D microscopy and massive data

They used 4D fluorescence light sheet microscopy to quantify the geometry (curvature) of the folded state, changes in curvature during the unfolding process, and the distribution of time required for unfolding. Through repeated trials, they demonstrated how collective ciliary activity can stably drive unfolding using scaling analysis and toy model simulations.Dryad

The public data is compiled on Dryad, totaling over 200GB. It includes data for each condition, such as epithelial curvature maps, folding on glass capillaries, conditions without substrates, and unfolding under drug conditions (e.g., LiCl).Dryad

This is a type of research that meticulously tackles phenomena that "surprise when seen in videos" through geometry and statistics, making it understated but strong.

How did the "earliest animals" acquire "shape"?

Researchers boldly delve into the topic of evolution. If the principles of morphological transformation without relying on the nervous system can be seen in early branching animals like Trichoplax, it raises the hypothesis that "shaping" was established through physics and collective motion before the invention of the nervous system.Phys.org

In embryonic development, epithelial folding commonly appears in brain wrinkles and organ formation junctions. This discovery reflects back on this "commonplace" from a more primitive perspective.Phys.org

Implications for engineering: Soft robots, synthetic biology, and "designable folds"

What makes this system interesting is that it is easily translatable into the language of design, not just in developmental biology and evolution. Viewing epithelial sheets as "thin active matter," the collective movement of cilia can "spontaneously" create shapes with minimal external control. In other words, for soft robotics and synthetic biology, it provides hints for creating three-dimensional shapes through the combination of **"material (sheet) + micro-actuation (cilia) + environment."**Dryad

Prakash Lab is known for its affinity with the concept of "folding = precision," having previously introduced shape changes in unicellular organisms as "cellular origami" (a different theme) and creating the Foldscope, a microscope made by folding paper. This "living origami" seems to be an extension of that line of research.Stanford News

Reactions on social media/internet: Three "striking points" that make it shareable

Despite the serious content of this news, it inherently contains elements that make it easily shareable online.

1. The "seems smart despite having no brain" issue
   When people hear "no nervous system," they tend to think "incapable of anything." However, in reality, "seemingly intelligent" phenomena occur through physics and collective motion. This is where the surprise lies.Phys.org

2. Strong visuals (origami × biology × video)
   To emphasize this capability, the research team reportedly introduced it through stop-motion videos using paper. It's a strategy that captures attention with "images" before text.Phys.org

3. Updating the image of "cilia"
   It breaks the stereotype of cilia being associated only with fluid, presenting a reinterpretation of "walking to shape." It conveys "new trivia" even to those outside the field.OUP Academic

Quantitatively, the relevant article on Phys.org had a "double-digit" reaction counter at the time of publication, separate from the comment section, indicating that it is at least a "type of topic that gets shared when found."Phys.org

Conclusion: Origami might not just be a metaphor, but a principle

This study challenges the assumption that "advanced shaping = advanced command center (brain)." With just thin sheets, tiny cilia, and contact with substrates, the dynamics of folding and unfolding emerge.Dryad

How did the earliest animals acquire "shape"? Why is folding so important in the development of our bodies? And in the future, can folding be "designed"?
The quiet and peculiar origami of Trichoplax seems to be an entry point to all of these questions.Life Science Network