Putting together the pieces of a microscopical jigsaw

The ability to put different pieces together to solve a problem comes naturally to Professor Thorsten Wohland, Director of the NUS Centre for BioImaging Sciences (CBIS), and Vice-Dean for Research and Space at the NUS Faculty of Science.

Prof Wohland began his university education at the Technical University of Darmstadt in Germany. As an undergraduate, he was interested in astrophysics and environmental physics and soon moved to the University of Heidelberg to follow these interests. However, when it came to choosing a project for his Master’s degree, he was so fascinated by optical tweezers – a device similar to the tractor beam in Star Wars to capture space ships, but on a microscopic scale – that he decided to work at the European Molecular Biology Laboratory to learn more about them. This brought him to the interface of physics and biology, a field he never left.

Today, Prof Wohland is a physicist investigating biology in NUS Biological Sciences and NUS Chemistry. He is a specialist in fluorescence spectroscopy, a tool for understanding the structure and behaviour of biological molecules, and his eclectic knowledge of physics, biology, chemistry and even computer science has helped him push the frontiers.

Capturing the dynamic behaviour of cells

Until now, despite having state-of-the-art microscopes, scientists are not able to clearly observe a living cell under a microscope. They can either take a high-resolution still photograph of the microscopic structures in the cell, or record a blur low-resolution video of the movement of molecules in the cell, but not both at the same time. This means it is impossible to see how molecules are moving and interacting with the fine structures in the cell and to understand how the cell really works.

Prof Wohland and his multidisciplinary team have literally put the pieces together. Their new technique coined “Simultaneous spatiotemporal super-resolution microscopy” is surprisingly simple. The first step is to snap many images at fast shutter speeds and small pixel size as the cell goes about its activities. This produces a pile of severely underexposed images. Then, the computer takes over.

The computer adds up the pixels vertically – through time – to get a bright, high-resolution image of cell structures. And it adds up the pixels horizontally – across space – to get bigger pixels that capture the movement of molecules. One can also statistically analyse how the number of molecules is changing and how this relates to the underlying cell structure.

The researchers used their new method to see how a common protein receptor moves around in the cell, and if it uses a cellular scaffolding called the cytoskeleton. They snapped 50,000 images at 500 frames per second, with more than 16,000 pixels in each image. Cameras were not fast enough to do this until recently.

What they found surprised them - the protein did not move about using the cytoskeleton as they had expected. Instead, it moved through the cell membrane while the cytoskeleton only had an indirect influence. As the behaviour of this protein is sometimes linked to cancer, this new knowledge could guide future cancer treatments.

Their discovery, which supports NUS’ key research area of biomedical science and translational medicine, was published in Nature Communications on 19 March 2021.

Prof Wohland is emphatic about not taking all of the credit for this breakthrough. “Science is a concerted effort and much of it happens progressively. This was a really long, slow but steady progress, including developments not only in our lab but in the field in general, towards what we have finally published now,” he said.

To further support scientific collaboration, Prof Wohland’s group has made their analytical software open source so other researchers can use it and even improve on it.

DIY super microscope

Prof Wohland is pushing his new technique even further into uncharted territory. Instead of getting images of a single layer, he wants to acquire multiple layers in a three-dimensional specimen.

Commercially available microscopes can no longer do the job, so he and his lab have built their own. In their microscope, a special lens turns the laser into a sheet of light just one micrometre thick. This light sheet can be moved through different parts of a sample to get 3D data. It can combine multiple lasers of different colours for identifying different molecules at the same time.

Balancing work and play

Besides tinkering with microscopes and squinting at computer codes, Prof Wohland makes sure he gets out of the lab for “extra-curricular activities” with his team. Cycling, ice-skating, barbecue, jungle hiking, exploring the village island of Pulau Ubin, spending a day at the beach - they have done it all, together.

It was on those occasions when new ideas sometimes appeared out of the blue. Prof Wohland shared, “I think many people have this experience that doing something unrelated relaxes you and allows you to back out of a dead-end and suddenly you can see the solution.”