By Akshita Thakur
“Black holes, quasars, supercomputers:nothing can compete with the complexity of even the most basic bacterial cell”
– Clifford P. Brangwynne
If we step outside on a misty morning, we can watch nature perform one of its miracles. Tiny droplets of dew begin forming on leaves, grass, and window panes as the cool air settles. Water simply condenses from the air, rearranging itself into shimmery beads. What if I told you that the very same phenomenon unfolds inside us, not on mountainsides or rooftops, but within our own cells, the building blocks of our body?
Biology textbooks taught us that cells are like a small bustling city, where organelles are like buildings that are surrounded by walls, separating the energy house of our cell, mitochondria, from the nucleus, the place where our genetic material is stored. But this picture was incomplete; cells also create reaction hubs without any membrane, known as membrane-less organelles (MLOs). Researchers have known about these organelles for well over a century. The nucleolus, for example, was described in the 1800s. They could see it under the microscope, dense, rounded but no membrane surrounding it. Stress granules, PML (Promyelocytic leukemia) bodies, and P-bodies are other examples that exist. They were seen as odd exceptions. Why do the components present in MLOs not mix with the surroundings? What organization could a cell use to form MLOs? We knew they existed but didn’t know what the underlying principle behind their organization was. The mystery was held for decades. Until something changed in 2009.
Clifford Brangwynne and Anthony Hyman in Max Planck Institute of Molecular Cell Biology and Genetics in Dresden studied cells from a roundworm (Perinuclear granules in C. elegans embryos), visualized them under a microscope, and observed a structure blobbing apart and then coalescing in lava lamp fashion. The structures (P granules) were behaving like oil droplets in water. We know that oil and water don’t mix; even a vigorously shaken bottle will eventually separate them into two distinct layers. These distinct layers are both liquids, segregating from each other due to different chemistries. The separation was occurring naturally because of a process called liquid-liquid phase separation (LLPS). It was a widely known principle to physicists, but not applied to cells. This was a paradigm shift, viewing these droplets as liquids. Once seen, it made sense. A new field was born.
Inside cells, proteins and nucleic acids follow similar rules. Under certain conditions, they cluster together and separate from their surroundings, forming a dense, droplet-like structure through a dance of molecular interactions. LLPS is the primary mechanism believed to generate these structures. Scientists now call these structures “bio-molecular condensates and they may act as micr-oreactors, bringing the right molecules together, and when the job is done, they dissolve. They can form and dissolve on timescales ranging from microseconds to several minutes or even hours, and that provides cells with extraordinary flexibility. This flexibility is what makes them so powerful and mysterious. Since 2009, the role of condensates has been extensively studied, leading to groundbreaking discoveries including their involvement in overall cellular maintenance, DNA repair, and regulating nucleic acids under stress conditions.
This elegant system also carries a risk; while these condensates are functionally relevant, problems arise when the balance is disrupted. Proteins that generally form dynamic, reversible droplets can become misfolded or sticky, leading to solid aggregates. This is linked to several neuro-degenerative disorders and cancer. Yet, condensates can be fascinating tools for scientists, because they gather molecules with precision and fall apart just as easily. One of the most important examples where this matters could be DNA repair. Although there is no consensus, many labs interpret the data differently.
DNA is the “instructional manual” of life, but it is vulnerable to sunlight and harmful chemicals, and it can break, just like a typo or tear in an instruction manual that can lead to errors if not repaired. DNA is double-stranded, its structure is like a twisted ladder, and double-stranded DNA damage is one of the most dangerous types, in which it is cut into two, if not correctly repaired, it can lead to cancer or neuro-degenerative disorders. Fortunately, our cells are amazing; they have special processes to repair DNA, but repairing DNA is not as simple as replacing a spare part with a machine. The cell needs to bring multiple proteins to the right place and right time. But how does a cell manage to multitask?
“Here comes phase separation to the rescue,” Ned Wingreen (Princeton University) said, emphasizing that when DNA suffers a double-stranded break, the repair proteins could form a droplet around it called a repair foci, repair it, and then eventually dissolve, though this idea is still under active investigation.
It is understood that repairing DNA is essential but studying it is another challenge. What if phase separation could be exploited to reconstruct the pathways in a simple and controlled system? Numerous studies have shown that the condensates are formed through predictable molecular interactions, and we can design such droplets that mimic the reactions happening inside our cells. These simple and controlled systems can provide a powerful way to dissect mechanisms involved in DNA repair in a highly tunable environment. It could bridge the gap between in vitro biochemistry and complex in vivo cellular biology.
Clifford Brangwynne said, “The cell is like a universe. Any place you point to with a very fine needle, you could spend a lifetime studying it. And people do” Cellular droplets are among the most fascinating discoveries in this universe, revealing to us the surprising and dynamic ways cells organize their inner world. Perhaps the most poetic twist is that phase separation in cells is not a modern way of looking at life; it may have helped create it. In the 1930s, biochemist Alexander Oparin proposed that early Earth’s organic molecules separated into primitive droplets called co-acervates. These droplets concentrate materials, enabling reactions that would have been impossible in dilute oceans. The discovery of bio-molecular condensates in modern cells supports the idea that life may have begun in droplets rather than membranes. A tiny, ancient dew drop could have been the first cradle of biology. In nutshell They highlight that cells use multiple strategies to coordinate their chemistry and these droplets remind us that cells can achieve remarkable organization without a wall.
(The writer is PhD Student, Plaksha University, Mohali)
