Summary: For decades, the primary cilium was dismissed as a useless evolutionary leftover. However, a new study reveals that this microscopic, antenna-like structure is a critical architect of the brain.
By analyzing over 1,000 mouse embryonic brains, researchers discovered that these cilia are packed with unexpected proteins linked to human developmental disorders. Most remarkably, the study found evidence that the cilium might actually manufacture its own proteins on-site, a discovery that challenges the fundamental “delivery-only” model of cellular biology.
Key Research Findings
- The Hidden Map: Researchers identified over 1,000 proteins within the primary cilia of neural progenitor cells, many of which were previously unknown to exist there.
- Regional Specialization: The cilium is not a “one-size-fits-all” structure; researchers found over 40 proteins that vary depending on which region of the brain the cilium is located in.
- The Protein “Bread Maker”: In a major shift for cell biology, the team discovered protein-making machinery inside the cilium. This suggests cilia may produce their own proteins locally rather than waiting for them to be transported from the main body of the cell.
- Ciliopathies and Filippi Syndrome: The study linked the protein CKAP2L specifically to the primary cilium. This protein is associated with Filippi syndrome (reduced brain size); when removed in mice, brain growth was significantly stunted.
- Early Development: Each neural progenitor cell possesses a single cilium that extends into the brain’s fluid-filled ventricles, acting as a sensor to guide early brain formation.
Source: UCR
A largely overlooked structure inside our cells may play a crucial role in how the brain forms, offering new insight into developmental disorders and potential therapies.
In a study published in Cell Reports, biomedical scientist Xuecai Ge at the University of California, Riverside and her team focused on the primary cilium, a microscopic, antenna-like structure found in nearly every cell in the human body. Despite its ubiquity, the primary cilium has remained surprisingly understudied.
“Even many biologists aren’t familiar with it,” said Ge, an associate professor of biomedical sciences in the School of Medicine. “We still have a lot to learn about this organelle.”
For decades, scientists believed the primary cilium was an evolutionary leftover with little function. But mounting evidence suggests otherwise. When the structure is disrupted, it can lead to a group of conditions known as ciliopathies, which affect multiple organs, including the brain.
“Patients may have kidney problems or obesity,” Ge said, “but when you look at their brain structure, you often see abnormalities. That made us wonder if the cilium had a role to play in brain development.”
To investigate, Ge’s team examined neural progenitor cells — early-stage cells that give rise to neurons. Each of these cells contains a single primary cilium that extends into the ventricles, fluid-filled cavities in the developing brain.
Using a large-scale biochemical approach, the researchers analyzed more than 1,000 mouse embryonic brains to identify which proteins are present in these cilia. What they found challenged existing assumptions.
“We discovered many proteins that no one expected to find in the cilium,” Ge said. “And in some cases, these proteins are directly linked to human developmental disorders.”
One such protein, CKAP2L, is associated with Filippi syndrome, a condition that leads to reduced brain size. When the researchers removed this protein in mice, the animals developed smaller brains.
The team also found that cilia differ depending on where they are in the brain.
“We identified over 40 proteins that vary between brain regions,” Ge said. “That suggests the cilium has specialized roles, not just a single uniform function.”
For Ge, the most surprising discovery was evidence that protein production might occur directly inside the cilium itself — a concept that challenges long-standing scientific beliefs.
“The field has assumed that all proteins are made elsewhere in the cell and then transported into the cilium,” Ge said. “But we found the machinery that could make proteins on-site. It’s like finding a bread maker where you thought bread could only be delivered.”
While further research is needed to confirm whether this machinery is active, the finding could represent a major shift in how scientists understand cellular function.
The implications extend beyond basic biology, according to Ge. Because ciliopathies can affect vision, organ function, and brain development, the research could help explain how these diseases arise and how they might be treated, she said.
“Understanding which proteins are in the cilium and what they do gives us a roadmap,” Ge said. “It helps us connect genetic mutations to the actual biological processes that go wrong.”
Looking ahead, Ge’s team plans to investigate which proteins are produced within the cilium.
“We’ve only scratched the surface,” she said. “There’s a lot more to learn about how this tiny structure shapes the developing brain.”
Ge was joined in the research by scientists at UC Merced and the Scripps Research Institute in La Jolla, California.
Funding: The study was supported by grants from the National Institutes of Health and National Science Foundation.
Key Questions Answered:
A: They are incredibly small and were long considered “vestigial”—like the cellular version of an appendix. It wasn’t until advanced biochemical mapping allowed scientists to see the specific proteins inside them that their role as a command center became clear.
A: It’s a massive shift. Traditionally, we thought the cell’s “factory” was centralized. If the cilium acts as a remote satellite factory, it means the brain can respond to developmental signals much faster and more precisely than if it had to wait for deliveries from the cell body.
A: It provides a “roadmap”. By identifying that CKAP2L malfunctions within the cilium, scientists can now focus on how to stabilize that specific protein or the cilium’s structure to prevent the reduced brain growth seen in these disorders.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper reviewed in full.
- Additional context added by our staff.
About this neurodevelopment research news
Author: Iqbal Pittalwala
Source: UCR
Contact: Iqbal Pittalwala – UCR
Image: The image is credited to Neuroscience News
Original Research: Open access.
“Proximity labeling proteomics maps radial glial ciliary proteins across the developing telencephalon” by Xiaoliang Liu, Oscar T. Gutierrez, Sabyasachi Baboo, Eva Cai, Gurleen Kaur, Yazan Al-Issa, Jolene K. Diedrich, John R. Yates III, and Xuecai Ge. Cell Reports
DOI:10.1016/j.celrep.2026.117355
Abstract
Proximity labeling proteomics maps radial glial ciliary proteins across the developing telencephalon
Primary cilia in radial glia act as signaling hubs essential for brain development, yet their molecular roles remain poorly understood.
Here, using proximity-labeling-mediated in vivo proteomics, we systematically mapped ciliary proteins in the developing telencephalon.
Our dataset reveals region-specific ciliary composition across the dorsal and ventral telencephalon. We identified and validated ribosome proteins and translational machinery components in radial glial cilia.
Further, we uncovered ciliary roles for neurodevelopmental disorder-associated proteins, including MARCKS, a key regulator of radial glial polarity, and CKAP2L, a protein linked to Filippi syndrome.
Functional studies show that MARCKS contributes to ciliogenesis and CKAP2L regulates neurogenesis by modulating Hedgehog signaling. These findings highlight previously unrecognized mechanisms by which primary cilia modulate brain formation.
Our in vivo ciliary proteomic dataset provides a unique resource for understanding ciliary functions in brain development and developmental disorders.
