Genetic engineers can design and assemble sophisticated gene circuits to program cells with new functions, but important signaling molecules can become diluted as these cells grow and divide, causing the synthetic gene circuits to lose their new functions.
Researchers at the School of Biological and Health Systems Engineering, part of the Ira A. Fulton Schools of Engineering at Arizona State University, report on a way to protect these fragile genetic programs using a principle borrowed straight from nature. Headed by associate professor Xiaojun Tian, PhD, the scientists have outlined a technique that can stabilize synthetic gene circuits by forming small, droplet-like compartments, called transcriptional condensates, inside cells through a process called liquid-liquid phase separation. These microscopic droplets act like molecular safe zones around key genes, shielding synthetically engineered modifications from being washed away by the tide of cell growth.
“When we try to program cells to perform useful tasks, such as diagnostics or therapeutic production, the genetic programs often fail because cell growth dilutes the key molecules needed to keep them running,” Tian explained. “We addressed this challenge by tapping into the cell’s own strategy of phase separation to protect engineered systems.”
In their published paper in Cell the team shows the potential for their strategy to boost production efficiency in a cinnamic acid biosynthesis pathway. Their results are reported in a paper titled “Phase separation to buffer growth-mediated dilution in synthetic circuits,” in which they concluded, “Together, our results establish liquid-liquid phase separation as an emerging design principle for constructing resilient synthetic circuits for robust performance under dynamic growth conditions.” The project harnessed interdisciplinary expertise in synthetic biology, modeling and metabolic engineering, from co-researchers including David Nielsen, PhD, a chemical engineering professor in the School for Engineering of Matter, Transport and Energy, part of the Fulton Schools at ASU, and Wenwei Zheng, PhD, an associate professor of chemistry in the School of Applied Sciences and Arts, also part of ASU’s Fulton Schools.
“Synthetic biology not only helps us understand the fundamental design principles of natural biological systems but also offers a powerful approach to constructing novel biological functions with applications spanning medicine, biotechnology, and environmental engineering,” the authors wrote. However, changes in host cell growth make it challenging to maintain reliability in synthetic gene circuit function across different conditions. “Growth-mediated dilution causes a global reduction in circuit component concentrations, which can significantly destabilize circuit behavior,” the team stated. “… there is a critical need for new strategies capable of maintaining consistent gene expression under dynamic growth conditions to ensure reliable circuit function across diverse environments.”
Cells use phase separation to organize their inner environment, creating compartments for essential biochemical reactions without the use of membranes. “Phase separation is widely utilized in both prokaryotic and eukaryotic systems to organize subcellular compartments, creating dynamic membraneless organelles that enhance specificity and efficiency of cellular processes,” the investigators continued. Tian’s team realized that by engineering similar condensates around synthetic genes, they could mimic this natural organization and maintain genetic stability across various cell generations.
“We discovered that by forming tiny droplets called transcriptional condensates around genes, we can protect genetic programs and keep them stable even as cells grow,” Zheng said. “It’s a simple physical solution that prevents dilution and keeps circuits running reliably.”
This approach represents a major shift from traditional strategies in synthetic biology, which have largely focused on tweaking DNA sequences or regulatory feedback loops to keep engineered systems functioning. Instead of more complex control systems, Tian’s team introduced a physical design principle that leverages the existing spatial organization of molecules inside cells. Summarizing the strategy, the team wrote, “By fusing transcription factors (TFs) to intrinsically disordered regions (IDRs), we drive the formation of transcriptional condensates that concentrate TFs at their target promoters. These condensates buffer against prolonged rapid dilution of TF concentration and preserve bistable memory in self-activation circuits across variable growth conditions.”
While natural cells have evolved to use condensates as a built-in protective system for regulating gene circuit activity, this study is among the first to show how it can be repurposed to stabilize synthetic programs. “Cells already use these droplets to regulate themselves,” Tian commented. “We’re now harnessing the same strategy for synthetic biology.”
Adopting this methodology could help researchers build more reliable biological systems that maintain predictable, productive functions. “This opens a new way to build more reliable living systems, from stable cell factories to future medical applications,” Tian added. “Our strategy can become a new design principle for researchers who need their engineered cells to work consistently.”
Images taken via microscope from the study show bright, glowing clusters of transcriptional condensates inside cells, which serve as visual proof that droplets can form precisely where needed to stabilize gene activity. “It’s exciting to see how these droplets can be used to boost bioproduction yields,” Nielsen stated. “This kind of collaboration bridges fundamental biological insights with real metabolic engineering applications.”
Tian’s group is already exploring how to engineer different kinds of condensates to control different genes, effectively turning them into programmable control hubs inside cells. “We want to program different condensates to control different genes, creating smart cells that can adapt and function long-term,” he noted. “We’re learning how to design with the cell, not against it.”
This approach to designing in accordance with nature rather than trying to override it represents a key turning point in the field. The next step is to demonstrate the technique’s applications for more diverse implementations to determine resilience and scalability, though researchers see no shortage in potential applications.
“Researchers in synthetic biology who struggle with unstable circuits will see this as a new way to make their systems more reliable,” Zheng suggested. “Bioprocess engineers who want a consistent yield can also use it. For biophysicists like me, it’s exciting to see physical principles like phase separation turned into practical engineering tools.”
“This work reflects a new direction in synthetic biology,” Tian said. “By using the cell’s own organizing principles, we can build systems that are both powerful and inherently stable.”
In their paper the team concluded that their studies “… highlight phase separation as a generalizable design principle for constructing gene circuits with improved stability and performance under dynamic growth conditions.”
