New method reveals how the brain and inner ear are formed

Researchers at Karolinska Institutet have developed a method that shows how the nervous system and sensory organs are formed in an embryo. By labelling stem cells with a genetic ‘barcode’, they have been able to follow the cells’ developmental journey and discover how the inner ear is formed in mice. The discovery, published in Science, could provide important insights for future treatment of hearing loss.

“Our study shows how different cell types arise from stem cells in the embryo and how they are organised to create important structures in the brain,” explains Emma Andersson, docent at the Department of Cell and Molecular Biology, Karolinska Institutet, Sweden. “You could say that we have created a family tree for the cells of the nervous system and the inner ear.”

Replacing damaged cells

The researchers used a technique where they injected a virus into mouse stem cells at an early stage of development. The virus contained a genetic ‘barcode’ that was integrated into the DNA of the stem cells and then inherited as the cells divided. By following this code, the researchers could track how the cells developed into different types of neurons and cells in the inner ear.

The results showed that cells in the inner ear, which are crucial for hearing, develop from two main types of stem cells. This knowledge could lead to new treatments for hearing loss.

“Tracing the origin and development of cells gives us a unique opportunity to understand the basic mechanisms behind hearing loss,” says Emma Andersson. “It can help us find new ways to repair or replace damaged cells in the inner ear.”

Exploring the nervous system

The team now plans to use the method to study other parts of the nervous system, but also how the rest of the body develops. They hope their work will lead to new insights and treatments for various genetic and developmental diseases.

“We are only at the beginning of understanding the complex processes behind nervous system development,” says Emma Andersson. “Our method opens up many exciting opportunities to explore how the nervous system and the rest of the body are formed during embryonic development. In addition, the technique can reduce the number of mice used in research.”

She led the study with Jingyan He, a postdoctoral fellow, and Sandra de Haan, a former PhD student in Emma Andersson’s research group. The research was funded by Karolinska Institutet, the European Union, the Erling-Persson Foundation, the Swedish Research Council, the Knut and Alice Wallenberg Foundation, the Hearing Research Fund, Horizon Europe and Wallenberg Bioinformatics Support. Co-author Jonas Frisén is a consultant for 10x Genomics. No other conflicts of interest are declared.

Publication: “Ectoderm barcoding reveals neural and cochlear compartmentalization”, Sandra de Haan, Jingyan He, Agustin A. Corbat, Lenka Belicova, Michael Ratz, Elin Vinsland, Jonas Frisén, Matthew W. Kelley, Emma R. Andersson, Science, online 3 April 2025, doi: 10.1126/science.adq9248.