Researchers at the German Cancer Research Center (DKFZ) have developed a new, streamlined method to isolate nuclei from long-term frozen pediatric glioma tissues—an innovation that could be a game-changer for studying rare brain tumors.

Studying tumors at the single-cell level has been a major breakthrough in understanding how cancer develops and evolves. By analyzing the genetic material of individual cells, researchers can uncover the complexity of tumors, revealing distinct populations of tumor cells, immune cells, and other components that make up a tumor. This detailed view is essential for understanding tumor heterogeneity—the fact that tumors are often composed of many different cell types with unique genetic profiles. However, most of these advanced techniques rely on fresh tissue samples, which are difficult to obtain for rare or hard-to-access tumors like pediatric gliomas.

The research team optimized a simple, cost-effective process for extracting intact nuclei from frozen tissues, making it easier to apply single-nucleus RNA sequencing (snRNA-seq) techniques to archived samples. Previously, working with frozen tissue often led to degraded genetic material, making it challenging to conduct accurate RNA sequencing. The new approach, however, ensures that intact nuclei are successfully isolated, even from long-term frozen samples, without compromising the quality needed for snRNA-seq.

Isolation of intact nuclei from long-term frozen pediatric glioma tissue

(a) Schematic figure showing sample preparation steps. (b) Representative images showing the effect of an increasing number of washing steps on nuclei yield/integrity and number of debris (scale bar 10 μm). (c) Nuclei yield decreases with increasing number of washes. Data are represented as mean with SEM. (d) Staining for nuclear membrane, DNA and RNA reveals intact nuclei, with no leakage of nucleic acids (scale bars 5 μm). Nuclei originate from a pediatric pilocytic astrocytoma tissue frozen for seven years prior to nuclear extraction. Created with BioRender.com, GraphPad Prism 5 and Affinity Designer 2.

The team tested their method across different sequencing platforms and confirmed that it works with both droplet-based and plate-based systems—two popular methods for single-cell RNA sequencing. They also optimized the sequencing process by including shorter RNA fragments in the 3′ sequencing library, improving the detection of genes and the ability to accurately annotate the different cell types within the tumor. This is especially important in brain tumors, where identifying various cell types, such as infiltrating immune cells like microglia, can reveal key insights into how the tumor grows and evades the immune system.

By successfully applying this method to pediatric gliomas, these researchers have demonstrated that this approach is not only feasible but also holds great promise for expanding research into rare brain cancers. Their technique allows for the analysis of previously inaccessible tumor samples, opening up new possibilities for discovering biomarkers, understanding tumor biology, and developing more personalized treatments for patients.

This advancement in RNA sequencing will significantly increase the potential of studying rare tumor entities, such as pediatric gliomas, that would otherwise be difficult to investigate due to limited tissue availability. In addition to its potential in cancer research, this method could also have broader applications in other areas of biomedical research where archived frozen tissues are available, but fresh samples are scarce.