New Optogenetic Method Restarts Cell Division After Centrosome Loss

Cell division depends on the centrosome, a membrane-less organelle built from more than 200 components that helps cluster the thread-like mitotic spindles needed to separate genetic material. Which parts of the centrosome are actually necessary and sufficient for this spindle assembly has long been unclear. Researchers at the Indian Institute of Science have now developed a technique called Light-Induced Spindle Activation (LISA) that can reversibly activate Aurora A kinase, a centrosomal enzyme critical for spindle assembly, using blue light. The study was published in EMBO Reports.

Scientists had thought Aurora A is activated through clustering, a process promoted by its scaffold protein Cep192. Earlier work showed that Aurora A-coated beads could trigger microtubule nucleation in frog egg extracts, but only with Cep192 present. LISA lets researchers induce and study Aurora A clustering independently of Cep192, across a range of cell types, and it works directly in living cells rather than only in extracts.

To build the method, Sachin Kotak and his team adapted an existing technique called LARIAT, normally used to inhibit proteins by clustering them with light, and repurposed it to activate Aurora A instead. LARIAT relies on the plant proteins CRY2 and CIB1, which cluster together in response to blue light. The team engineered human cells to express a fusion protein linking Aurora A kinase to CRY2; when blue light hits the fusion protein, CRY2 changes shape and binds CIB1, driving multiple Aurora A assemblies to cluster. “This provides a novel way to trigger and activate an artificial Aurora A kinase complex – Aurora A fused to light-sensitive plant proteins, which is sufficient to induce microtubule nucleation,” says Vignesh Olakkal, first author of the study.

Cells lacking centrosomes typically show spindle assembly defects that disrupt division. To test whether LISA could compensate, the team chemically removed centrosomes from human cells, introduced the engineered Aurora A system, and applied blue light during mitosis. This induced Aurora A clustering, stimulated microtubule nucleation, and was sufficient to restore spindle assembly and rescue the division defects caused by centrosome loss.

The researchers also see therapeutic potential. “In many solid tumors, Aurora A kinase is overexpressed, and that’s why there are drugs targeting it. But Aurora A kinase has multiple targets,” Kotak explains. “Now, with our strategy, we can find out what the Aurora A kinase-specific targets are, independent of the centrosome, as far as microtubule nucleation is concerned. Then we will hopefully be able to find other targets of Aurora A kinase and design drugs.”