In many cells of the human body, hair-like protrusions known as cilia act as antennae, allowing cells to receive signals from their environment and other cells. As cells grow and divide, each cilium must first form on the cell body, then disassemble — or break down by shedding or shortening — before the cell divides.
Many genes involved in cilia formation have been previously studied, and mutations in these genes are known to cause a host of pediatric disorders, or ciliopathies, that impact the formation of bodily systems like the skeleton, heart, and brain.
However, scientists have known little about which genes play a role in allowing cilia disassembly to occur, as well as how defects in the process impact the body.
In a new study, a Yale research team has identified a series of genes that make up a pathway responsible for the disassembly of primary cilia (a type of single, immobile cilia found in some cells) — and, when defective, may be linked to a neurological disorder called focal cortical dysplasia.
“Our goal was to use new genomic technologies to systematically approach the question of cilia disassembly,” said David Breslow, an associate professor of molecular, cellular, and developmental biology in Yale’s Faculty of Arts and Sciences, and the study’s corresponding author. “We uncovered fundamental aspects of how cells work that hadn’t been well understood, as well as a potential new connection to a disease that could help us understand its causes and therapeutic strategies.”
The results were published on Oct. 29 in Science Advances.
Studying cilia disassembly could lead to better therapies for neurologic disease, as well as other conditions, including cancer, to which the abnormal breakdown of cilia might contribute.
The study’s lead authors are, from left, Shane Elliott, a former graduate student at the Breslow Lab, and Paul Ready, a former post-graduate researcher at the lab.
Previously, Breslow said, members of his lab began using CRISPR (“clustered regularly interspaced short palindromic repeats”), a gene-editing technology, to identify the genes needed for cells to build primary cilia. To do so, they “knocked out,” or inhibited, the function of every gene in the genome, a technique that allowed them to link certain genes to diseases associated with faulty cilia formation.
They then turned their focus to a less-studied process: cilia disassembly.
“Here, we turned that prior technology on its head,” said Breslow, who is also a member of the Wu Tsai Institute and the Yale Cancer Center. “Instead of asking what genes in the genome lead to defects in primary cilia when we inhibit their function, now, we asked which genes impair primary cilia when we increase their function.”
To perform this new type of genetic screen, the researchers used CRISPRa (CRISPR activation), a variation of CRISPR that allowed them to increase the activity of every gene in the genome. The scale of this experiment, Breslow said, was technically beyond reach until recently.
Using this technique, the researchers were able to identify two genes — F2R and SARM1 — that caused cilia loss when their activity increased, or they were “overexpressed.” Together, when functioning typically, these genes form a key pathway for cilia disassembly and help maintain normal ciliary function by regulating the balance of cilia assembly to disassembly.
Their second discovery, however, was more serendipitous.
After the researchers found the pathway, they began to question how its function could impact physiology. They found a possible answer in a research paper that identified the set of genes mutated in patients with focal cortical dysplasia, a neurodevelopmental disorder that causes seizures. To their surprise, the mutated genes included several of the same genes that made up the cilia disassembly pathway.
The overlap signals a potential key role that ciliary dysfunction might play in focal cortical dysplasia. It also points to the possible physiological impacts of the cilia disassembly pathway identified by the researchers.
“Ultimately, by manipulating this pathway, we could develop treatments that would help restore cilia in diseases caused by too much cilia disassembly, with cortical dysplasia being potentially an example of that,” Breslow said.
The team hopes to continue their research into cilia disassembly and the role ciliary dysfunction plays in focal cortical dysplasia.
“We’re hoping that getting some new insights into cilia disassembly will help to accelerate or catalyze the next discoveries,” said Breslow. “There are some indications that cilia disassembly could be altered in neurological disease, as we mentioned in this paper, but maybe also in other conditions including cancer. It’s something that we’re excited to further explore.”
The study’s lead authors are Shane Elliott, a former graduate student at the Breslow Lab, and Paul Ready, a former post-graduate researcher at the lab (now at GSK and the University of Minnesota, respectively). Other co-authors from the Breslow Lab include researchers Caitlin M. Wrinn, Qianqian Ma, Jingbo Sun, Ceara K. McAtee, and İrem Sude Atiş.
Co-authors from the Yale School of Medicine include Anthony Koleske, the Ensign Professor of Molecular Biophysics and Biochemistry and of Neuroscience; and Angélique Bordey, the Rothberg Professor of Neurosurgery (both also members of the Wu Tsai Institute), along with researchers Marina Edward, Robert F. Niescier, and Iris Escobar (now at Envisagenics).
Grants from the National Institutes of Health and the Smith Family Foundation supported this research.
