The genetic disorder Fragile X syndrome occurs when individuals don’t make the Fragile X protein known as FMRP. Essential for normal brain development, FMRP helps control when and where proteins are made in the brain, supporting its ability to change and adapt in response to things we experience and the environment around us.

Determining exactly how FMRP exerts such influence in the brain is key to developing new treatments for Fragile X but has proven a tough nut to crack.

In a new study in the journal Molecular Cell, scientists at the University of Rochester School of Medicine & Dentistry clarify how the FMRP protein works and what happens when it’s missing, like in patients with Fragile X.

The research, which challenges the predominant theory in the field, establishes a new foundation for developing therapies from the scientific ground floor—fundamental knowledge of how the molecules in our cells function and interact—and up.

Applying the brakes

RNA biologist and senior study author Lynne Maquat, Ph.D., describes FMRP as a molecular brake pad in brain cells. Proteins need to be produced at very precise times and places to support learning and memory, allow us to adapt to new experiences, and respond to injury.

Like lifting your foot off the brakes in your car when a traffic light changes from red to green, FMRP lifts the brakes and permits protein production in a cell once it gets the appropriate signal from the brain. FMRP does this by interacting with our messenger RNAs, or mRNAs.

mRNAs carry genetic instructions from the nucleus to the body of the cell, where the instructions can be translated into proteins. Maquat’s team discovered that FMRP physically sequesters approximately one-fourth of our mRNAs—gathers and protects them while preventing them from making protein—and transports them to specific locations in brain cells.

Once FMRP delivers the mRNAs to the desired location, safe and intact, it waits for a signal from the brain that says, “lift the brakes.” FMRP then unleashes the mRNAs to make the desired proteins.

When FMRP is absent, like in Fragile X, there is no brake. Imagine a busy intersection full of cars with no brakes; turmoil and damage are inevitable. The same is true for the brain without FMRP; mRNAs travel through cells unchecked, haphazardly producing protein. This unregulated environment creates chaos in the brain and contributes to the cognitive and behavioral symptoms seen in Fragile X syndrome.

“Currently there is no cure for Fragile X and available treatments are inadequate; we need more options for patients,” said Maquat, founding director of the University of Rochester Center for RNA Biology and the J. Lowell Orbison Endowed Chair and Professor of Biochemistry & Biophysics at the School of Medicine & Dentistry.

“Clinical trials are always based on findings in fundamental research. We need to figure out exactly what the molecules in our cells are doing to generate therapeutic targets and tools. Until we understand what is going on at the most basic level, we’re shooting in the dark.”

The scientific process at work

The team analyzed FMRP activity in mouse and human brain cells. Previously, scientists believed that FMRP ensured proteins were produced at the right time and place through a process called ribosome stalling.

They theorized that FMRP triggers the protein-making machinery in the cell (the ribosome) to pause in the process of turning the genetic instructions in mRNA into protein; then once FMRP got the appropriate signal from the brain, protein production would resume.

Through meticulous cell-based experiments and imaging analysis, Maquat’s team showed that FMRP isolates and insulates mRNAs—rather than stalling mRNAs—to make sure proteins are produced when and where they are needed in the brain.

“When you are pushing up against established findings, you need to be confident in your work,” said Chris Pröschel, Ph.D., study author and professor of Biomedical Genetics at the University of Rochester School of Medicine & Dentistry. “The team conducted an exhaustive number of stringent tests, with many checks and balances, to make this discovery.”

“This is the scientific process at work. People come up with ideas and test them; others review the findings, ask different questions, and do more research,” added Pröschel. “We don’t always have the answer, but we build off past knowledge to learn more. Science is key to solving problems now and in the future.”

With this new knowledge in hand, the team is now using the powerful imaging technology called cryogenic electron microscopy, or cryo-EM, and the related technology, cryogenic electron tomography, or cryo-ET, to visualize the structures of mRNAs that are insulated by FMRP.

“Using cryo-EM and cryo-ET together with what we have already learned from biochemical techniques, we hope to be able to define at the atomic level how FMRP silences mRNAs from synthesizing proteins,” noted Maquat.

“We plan to track structural changes in neurons as these mRNAs move to where they start making proteins. These are lofty goals that come with technical challenges, but with Chris Pröschel driving the neurobiology aspects and Makaia Papasergi-Scott driving cutting-edge cryo-EM and cryo-ET, we have the expertise here at the University of Rochester to make real headway.”

“It is easy to see how difficult life can be for kids with genetic disabilities like Fragile X,” said Elizabeth Abshire, Ph.D., study author and postdoctoral researcher in the Maquat Lab.

“We want to help children and families, but we have to understand how things work normally to fix them when they are broken. Now that we know how FMRP functions—what ‘normal’ looks like—we can begin to think about designing therapies.”