Ultrasound has been used successfully to view gene expression in mammalian cells, in a development that could transform cellular imaging technologies.

Methods of visualising gene expression in cells are essential to enable continued advances in genomic medicine. Fluorescent techniques are currently the most widely used cellular imaging technique, despite their limitations. Fluorescent ‘tags’ can be placed on genes, so they glow brightly when expressed. However, this technique cannot penetrate deeply through tissues and does not illuminate the regulatory genes. Using ultrasound could prove an easier and more effective imaging technique.

Ultrasound probes emit high frequency sound pulses. When the ultrasound waves reach a tissue boundary, such as between bone and muscle, some waves reflect back whilst others keep travelling through. By analysing the varying distances the waves travelled before they were reflected back, a 2D image is produced. To allow gene expression to be viewed by ultrasound, mammal cells were engineered to express tiny protein compartments that acts as a contrast agent for the ultrasound waves, mimicking a tissue boundary.

To enable the cells to express the protein compartments, nine bacteria genes were translated into the cells with the aid of a virus. The virus tricked the cells into expressing multiple genes from one piece of RNA, whilst in normal body cells usually only one gene is expressed from each piece of RNA.

The ultrasound technique generated high resolution images of gene expression of living mammals, providing the cell volumetric density was less than 0.5%.

The researchers state that their work could have immediate applications to monitor cellular location and function inside living organisms. However, they stress that further optimisation would be needed to make their technique as widely used as fluorescent imaging.