Location Matters: How The Nuclear Geography Of circRNAs Could Shape The Future Of RNA Therapeutics
By Andre Brezski, Ph.D., Research Scientist, Institute of Molecular Biosciences, Goethe University Frankfurt
For much of RNA biology, the emphasis has been on understanding sequence, structure, and function. These remain the foundations of the field, but another dimension is increasingly coming into focus: location.
Where an RNA molecule resides within a cell is not simply a matter of cellular organization. Localization influences which proteins an RNA encounters, which regulatory pathways it participates in, how long it persists, and ultimately what biological role it can perform.
This principle is particularly relevant for circular RNAs (circRNAs). While significant progress has been made in identifying thousands of endogenous circRNAs and exploring their potential as therapeutic platforms, relatively little attention has been given to their spatial organization inside the nucleus.
In a recent study, our team sought to address this question by systematically examining the distribution of circRNAs across multiple subnuclear compartments. Rather than viewing the nucleus as a homogeneous environment, we investigated how circRNAs are organized within distinct nuclear domains that perform specialized biological functions.
Our findings suggest that circRNA localization is far from random. Instead, many circRNAs display distinct patterns of enrichment within specific nuclear compartments, providing new clues about how these molecules are regulated and how they may contribute to cellular homeostasis.
Although this work is fundamentally a study of RNA biology, it also raises broader questions for the RNA therapeutics community. As synthetic RNA platforms continue to evolve, understanding where RNA functions may become just as important as understanding what RNA encodes.
The Nucleus Is A Highly Organized Landscape
The nucleus is often depicted as a simple container for genetic material, but in reality, it is one of the cell’s most highly organized structures. Specialized domains (nuclear speckles, nucleoli, Cajal bodies, histone locus bodies, paraspeckles, and other membrane-less compartments) serve as centers for transcription, RNA processing, ribosome biogenesis, chromatin organization, and gene regulation. These structures create localized biochemical environments where specific proteins and RNA molecules interact with remarkable precision.
For linear RNAs, nuclear localization has been studied extensively. Certain transcripts are retained within nuclear compartments, while others are rapidly exported to the cytoplasm. These localization patterns influence RNA processing, maturation, and function. CircRNAs, however, have largely remained an exception. Although considerable effort has focused on their biogenesis and biological activity, comparatively little has been known about their spatial organization within the nucleus.
Mapping The Nuclear Geography Of circRNAs
Our study systematically analyzed circRNA localization across multiple subnuclear compartments. Rather than finding a uniform distribution, we observed that circRNAs exhibit distinct localization patterns. Some are enriched within particular nuclear domains, while others appear largely excluded from them.
These observations suggest that circRNAs participate in highly organized intracellular networks rather than diffusing randomly throughout the nucleus. Importantly, localization itself does not establish function. However, it provides valuable clues.
When RNA molecules consistently accumulate within particular cellular environments, it suggests that those locations may support specific biological activities or regulatory interactions. Just as proteins often reveal their function through where they localize, circRNAs may also provide functional insight through their spatial organization.
Why Localization Matters
RNA function depends on opportunity. An RNA molecule can interact only with proteins, enzymes, and regulatory complexes that occupy the same cellular space. Consequently, localization determines which molecular interactions become possible. This perspective encourages researchers to think about RNA biology in a more integrated way. Sequence establishes potential. Structure determines accessibility. Localization creates opportunity. Together, these properties shape RNA function.
For circRNAs, understanding localization may help explain why certain molecules participate in transcriptional regulation, RNA processing, or other nuclear activities, while others function primarily within the cytoplasm.
Implications For Engineered circRNAs
CircRNAs continue to generate excitement as potential therapeutic platforms because of their stability and ability to support sustained protein expression. Current development efforts focus on improving circularization efficiency, manufacturing, delivery, translation, and immunogenicity. These remain essential priorities. At the same time, studies of endogenous circRNAs suggest another consideration may eventually become important: intracellular destination.
Most therapeutic development understandably asks whether an RNA reaches the correct tissue or cell type. Future RNA engineering may also need to ask where that RNA ultimately resides after entering the cell. Does it remain in the nucleus? Is it exported efficiently? Does it localize to specific subcellular environments that influence its activity?
Although these questions remain largely unexplored, understanding endogenous localization patterns provides an important biological foundation.
Learning From Endogenous RNA Biology
One recurring theme in RNA therapeutics is that nature often provides the blueprint for engineering. Messenger RNA therapeutics benefited from decades of research into translation and RNA modification. Small interfering RNAs emerged from studies of endogenous RNA interference pathways. Similarly, understanding how naturally occurring circRNAs are processed, transported, and localized may ultimately inform the design of future synthetic circRNA platforms.
This does not imply that therapeutic circRNAs should simply mimic endogenous molecules. Rather, studying endogenous biology helps identify the principles that determine RNA behavior inside cells. Those principles can then guide engineering strategies.
From Delivery To Intracellular Precision
RNA therapeutics have progressed rapidly by solving increasingly complex challenges. The earliest questions focused on stability. Attention then shifted toward delivery, manufacturing, and immune compatibility. As these technologies mature, another frontier may emerge: intracellular precision.
Successfully delivering RNA into a target cell may represent only one step in achieving optimal therapeutic performance. Understanding how RNA molecules navigate intracellular environments, and how those environments influence RNA activity, could become an equally important aspect of future platform development.
Our findings do not yet provide answers to these engineering questions. However, they contribute an important resource for exploring them. By establishing a systematic view of circRNA localization within subnuclear compartments, this work expands the framework through which researchers can investigate circRNA biology.
Looking Ahead
CircRNAs continue to surprise us. Initially regarded as rare splicing byproducts, they are now recognized as abundant and functionally diverse components of gene regulation. Their potential as therapeutic molecules continues to grow as researchers develop increasingly sophisticated approaches to RNA engineering.
As this field advances, understanding circRNAs will require more than cataloging sequences or measuring expression levels. It will require understanding the complete biological context in which these molecules operate. Location is one component of that context. Our study suggests that circRNAs occupy defined positions within the nuclear landscape, opening new avenues for investigating how spatial organization contributes to RNA function.
For the RNA therapeutics community, this represents more than an interesting biological observation. It highlights an emerging principle that may shape future innovation: designing effective RNA medicines may ultimately require not only the right sequence, the right chemistry, and the right delivery system but also an appreciation for where RNA functions once it reaches its cellular destination.
About The Author
Andre Brezski, Ph.D., is a research scientist in the Institute of Molecular Biosciences at Goethe University Frankfurt, where his work focuses on the computational analysis of circular RNAs (circRNAs), including their biogenesis, nuclear localization, and biological functions. He earned his doctorate in bioinformatics from Goethe University Frankfurt, where his dissertation explored the regulation and subnuclear distribution of circRNAs. His research combines bioinformatics, transcriptomics, and RNA biology to better understand how RNA localization and processing influence gene regulation.