Cells dividing in our body seen like never before

Researchers at the University of Michigan have developed a groundbreaking superresolution technique that allows for detailed observation of cell division at the nanoscale.

This innovative method, which does not rely on molecules that degrade with prolonged use, has opened up new possibilities in the field of biology.

Superresolution microscopy, a technique that can reveal structures as small as 10 nanometers - roughly the width of 100 atoms, has revolutionised biological research since its inception, earning a Nobel Prize in 2014.

However, its limitation lies in its inability to observe cellular processes over extended periods, as it can only capture snapshots within tens of seconds. The team, led by Somin Lee, assistant professor of electrical and computer engineering at the University of Michigan, sought to overcome this limitation.

"We were wondering—when the system as a whole is dividing, how do nanometer-scale structures interact with their neighbors at the nanometer scale, and how does this interaction scale up to the whole cell?" said Lee.

To answer this question, they developed a new kind of superresolution that allowed them to continuously monitor a cell for an impressive 250 hours.

Unlike the original method that used fluorophores - fluorescent molecules that emit light when illuminated, the new technique employs gold nanorods as probes.

These nanorods, which do not break down with repeated exposure to light, respond to the phase of the light, depending on their angle to the incoming light. The nanorods can attach to specific cell structures, such as actin, a protein that provides structure to soft cells.

To locate the nanorods, the team constructed filters from thin layers of polymers and liquid crystals. These filters enabled the detection of light with a particular phase, allowing the team to identify nanorods with specific angles to the incoming light.

By merging multiple images, each focusing on a different subset of nanorods, the team was able to deduce the nanometer-scale details of the filaments inside the cells.

Through this technique, the researchers discovered three rules governing the self-organisation of actin during cell division. Actin is a protein that forms the contractile filaments of muscle cells, and is also involved in motion in other types of cell.

They found that actin expands to reach its neighbors when filaments are far apart, draws nearer to increase connections, and contracts when more connected while expanding when less connected.

The team plans to further explore the relationship between the behavior of actin and the cell, particularly why their motions are opposite at different scales. They also aim to investigate the potential implications of dysregulating this molecular process in disease development.

Ultimately, they hope to use superresolution to understand how self-organisation is built into biological structures, without the need for central control.