Mapping the Hidden Regulators of Translation

Systematic discovery of ribosome-associated proteins across development, immunity, and disease

For decades, ribosomes were viewed as uniform molecular machines—passive participants in gene expression that translate mRNA into protein with little selectivity. This classical view positioned regulation upstream, in DNA and RNA, while the ribosome itself was considered invariant.

Our work challenges this paradigm.

We now understand that ribosomes are embedded within a dynamic and complex regulatory environment shaped by ribosome-associated proteins (RAPs)—factors that bind to ribosomes and modulate how, when, and which mRNAs are translated. Despite their importance, RAPs have remained largely unexplored due to the lack of technologies capable of systematically identifying them across biological contexts.

To address this, we developed RAPIDASH (Ribosome-Associated Protein Identification and Discovery Across Sample Hierarchies)—a tag-free, broadly applicable platform that enables enrichment and identification of ribosomes and their associated proteins from virtually any sample . This approach overcomes major limitations of prior methods and allows, for the first time, a global and unbiased view of the molecular environment of ribosomes across development, physiology, and disease.

A global view of ribosome-associated proteins

Applying RAPIDASH across multiple biological systems, we identified hundreds of candidate RAPs, dramatically expanding the known landscape of proteins that interact with ribosomes . These include not only canonical translation factors but also RNA-binding proteins, metabolic enzymes, signaling molecules, and previously uncharacterized regulators.

Importantly, RAPIDASH captures a highly enriched and biologically meaningful set of ribosome-associated factors, with strong overlap with existing approaches while revealing many additional candidates . This establishes RAPIDASH as both a sensitive and specific platform for defining ribosome composition.

These findings reveal that ribosomes are not isolated machines, but rather exist within a rich regulatory network that integrates multiple layers of cellular information.

Ribosomes as drivers of neural development

LLPH reveals selective translation of long, neuron-specific mRNAs

One of the most striking insights from this work is that ribosome composition is not only tissue-specific—but functionally instructive, particularly in the nervous system.

Using RAPIDASH to profile embryonic mouse tissues, we uncovered a set of forebrain-enriched ribosome-associated proteins, demonstrating that ribosomes in the developing brain are molecularly specialized . These include RNA-binding proteins and signaling molecules linked to neurodevelopment, suggesting that translational control is tailored to the unique demands of neuronal cells.

Among these, we identified LLPH as a previously uncharacterized ribosome-associated protein with a critical role in neural development . Functional studies revealed that LLPH regulates the translation of a specific class of mRNAs—those with long coding sequences. This is particularly significant because many genes essential for neuronal identity, connectivity, and signaling fall into this category.

Rather than globally affecting protein synthesis, LLPH enables selective translation, acting as a molecular filter that ensures efficient production of long, complex neuronal proteins. In its absence, these transcripts are disproportionately affected, leading to defects in neural development.

This discovery establishes a key principle:ribosome-associated factors can define which classes of mRNAs are translated.

More broadly, these findings suggest that ribosomes actively shape developmental gene expression programs. By associating with specific regulatory proteins such as LLPH, ribosomes gain the ability to preferentially translate subsets of transcripts critical for cell identity.

This reveals a new layer of regulation in neurodevelopment—one in which ribosome composition itself encodes selectivity, ensuring that the correct proteome is produced to build and maintain the nervous system.

Dynamic remodeling of ribosomes in immune responses

Ribosome composition is not static—it is dynamically remodeled in response to environmental signals. To explore this, we applied RAPIDASH to macrophages undergoing activation by bacterial and viral stimuli.

Upon stimulation, we observed extensive changes in ribosome-associated proteins, with hundreds of RAPs differentially enriched over time . These include proteins involved in innate immune signaling, RNA sensing, and antiviral defense.

Notably, we identified cytoplasmic RNA sensors, including members of the OAS family, associating directly with ribosomes during immune activation. This suggests a model in which ribosomes themselves may act as platforms for detecting viral RNA and coordinating translational responses.

In addition, interferon-stimulated proteins such as Viperin and CMPK2 were enriched on ribosomes, linking immune signaling pathways directly to translational control. These findings demonstrate that ribosomes are dynamically reprogrammed during immune responses, enabling rapid adaptation of protein synthesis to environmental challenges.

Ribosome remodeling in disease and cellular states

Beyond development and immunity, RAPIDASH reveals that ribosome composition is sensitive to cellular state, including in disease contexts such as cancer . These changes likely contribute to altered translational programs that support pathological processes.

More broadly, ribosomes emerge as adaptive platforms, whose composition is continuously tuned in response to differentiation, signaling, and environmental conditions. This dynamic remodeling provides a mechanism for integrating diverse inputs directly at the level of protein synthesis.

A new framework for gene regulation

Together, this work establishes a new framework for understanding translation. Ribosomes are no longer viewed as passive machines, but as active regulatory hubs, whose function is shaped by their associated proteins.

RAPs provide a mechanism for:

• Selective translation of specific mRNA classes

• Integration of signaling pathways directly at the ribosome

• Spatial and temporal control of protein synthesis

• Adaptation to developmental and environmental cues

By enabling systematic discovery of RAPs across biological contexts, RAPIDASH reveals a previously hidden layer of gene regulation.

Looking forward

RAPIDASH provides a powerful and broadly applicable platform for exploring ribosome biology in its native context. Its ability to work across tissues, cell types, and conditions opens new opportunities to understand how translational regulation is rewired in development, neuroscience, immunity, and disease.

More fundamentally, this work advances a paradigm shift:

Gene expression is not solely encoded in DNA or mRNA—it is also shaped by the ribosome and its associated regulatory landscape.

By uncovering this layer of control, RAPIDASH reveals that the ribosome is not just a machine—but a central decision-making hub in gene expression.

Susanto TT, Hung V, Levine AG, Chen Y, Kerr CH, Yoo Y, Oses-Prieto JA, Fromm L, Zhang Z, Lantz TC, Fujii K, Wernig M, Burlingame AL, Ruggero D, Barna M. RAPIDASH: Tag-free enrichment of ribosome-associated proteins reveals composition dynamics in embryonic tissue, cancer cells, and macrophages. Mol Cell. 2024 Sep 19;84(18):3545-3563.e25. doi: 10.1016/j.molcel.2024.08.023. Epub 2024 Sep 10. PMID: 39260367; PMCID: PMC11460945.