IISc scientists control human cell division with a flashing blue light

In a major leap for synthetic biology, researchers at the Indian Institute of Science (IISc) in Bengaluru have found a way to control human cell division with flashes of blue light. The team has successfully engineered a biological remote control that can trigger the assembly of the microscopic machinery necessary for a cell to split into two. This technique, dubbed Light-Induced Spindle Assembly or LISA, bypasses the incredibly complex natural structures usually required for this process. The breakthrough answers a long-standing question in cell biology and opens fresh avenues for understanding developmental disorders and cancer.

Cells normally divide with a process known as mitosis. When a cell prepares to split, it must divide its DNA perfectly so each new daughter cell receives an identical copy. To physically pull the chromosomes apart, the cell builds a temporary scaffolding called the mitotic spindle, made of long, thread-like structures called microtubules. In human cells, the main factories that organise these microtubule threads are organelle structures called centrosomes. Centrosomes are colossal molecular machines made of more than 200 different proteins. For years, scientists have been trying to understand the minimum ingredients needed to jump-start this factory.

One of the most critical ingredients is an enzyme known as Aurora A kinase. Under normal circumstances, Aurora A sits at the centrosome and is activated by a large scaffold protein called Cep192. However, scientists debated whether this scaffold was strictly necessary, or whether its only job was to bundle many Aurora A molecules close together. To test this, the researchers turned to optogenetics, a technique that uses light to control cell behaviour. They engineered human cells so Aurora A proteins were attached to a special plant-derived, light-sensitive module.

Key context and latest developments

When the researchers shone a brief pulse of blue light onto these modified living cells, the Aurora A proteins rapidly clumped together within seconds. Astoundingly, simply forcing these proteins into a tight cluster was entirely sufficient to switch them on. Activated Aurora A then recruited a partner protein called TPX2 and began sprouting the microtubule threads needed for the mitotic spindle. The team proved that the massive Cep192 scaffold was completely unnecessary. Even more remarkably, when the researchers intentionally destroyed the cells’ centrosomes- a catastrophic event that usually leaves a cell struggling to divide, resulting in severely delayed and chaotic replication- repeated flashes of blue light restored normal division. The light-induced clusters stepped up, mimicking the missing centrosomes and rescuing the cells from division failure.

In the past, scientists modelled mitosis by coating microscopic artificial beads with Aurora A and injecting them into extracted frog egg fluid. While informative, that older method was technically exhausting, restricted to a cell-free soup rather than a living human cell, and strictly depended on the presence of the Cep192 scaffold. Furthermore, the bead method was permanent. In contrast, the new LISA system operates directly inside living human cells and is fully reversible. As soon as the blue light is turned off, the Aurora A clusters dissolve, allowing scientists to repeatedly turn the enzyme on and off like a light switch. Interestingly, the researchers achieved this by repurposing a pre-existing optogenetic tool called LARIAT, which was originally designed to trap and turn off cellular proteins. The team ingeniously co-opted this logic, showing that for proteins that rely on proximity, the trap could be used as an activator.

The scientists, however, noticed that shining blue light on cells that were in their resting phase, rather than actively dividing, caused the proteins to cluster but failed to activate them. This suggests that simply bunching the proteins together is not enough. The activation also requires the specific chemical environment of a dividing cell, likely because crucial partner proteins are locked away in the cell nucleus until the division process officially begins. Additionally, while the team knows that the partner protein TPX2 is recruited to the light-induced clusters, they note that fully understanding the complete molecular recipe of these new assemblies will require further biochemical mapping in the future.

Flaws in cell division and the misregulation of the Aurora A protein are heavily linked to the aggressive, uncontrollable cell growth seen in various cancers, as well as several developmental disorders. By providing a precise, reversible, and simple method to activate cell division machinery on demand, this research gives the global scientific and medical community a new clinical intervention. It also lets pharmaceutical researchers better screen for cancer-fighting drugs in a highly controlled environment. Moreover, it provides a vital tool for studying fertility and reproductive biology, since human eggs and sperm naturally divide without traditional centrosomes. With a simple flick of blue light, scientists are now one step closer to unravelling the deepest mechanics of human life and disease.