The recent findings published in Molecular Cell reveal detailed insights into the internal organization of the cytoplasm, the intricate milieu of liquid, organelles, proteins, and other molecules within a cell. The research emphasizes the critical influence of the specific location within the cellular environment where messenger RNA (mRNA) undergoes translation into proteins.
Dr. Mayr, a molecular and cell biologist at the Sloan Kettering Institute, describes the significance of the study by drawing a parallel with the real estate adage, “location, location, location,” highlighting that this principle also applies to the cellular processes of protein synthesis. The research demonstrates that the location of mRNA translation within the cytoplasm significantly impacts the amount of protein produced.
This groundbreaking study not only contributes to our understanding of fundamental cellular biology but also holds potential implications for enhancing or modifying protein production in mRNA-based vaccines and therapies.
The study was spearheaded by Dr. Ellen Horste, a former lab member of Dr. Mayr, who embarked on the challenging project several years ago. Dr. Horste, now working for a gene therapy company, led the effort to color-code individual particles within cells using antibodies and then systematically sorted them by color. The team employed RNA sequencing to identify the specific RNAs associated with each particle.
Dr. Mayr expresses pride in the project, noting its challenging nature and emphasizing the impressive work of Dr. Horste. The approach adopted by the team involved adapting techniques commonly employed by immunologists, allowing them to isolate and study individual components within cells. The results revealed distinct intracellular neighborhoods where different types of mRNAs were being translated, providing valuable insights into the intricacies of cellular organization.
Step into the cellular community
Within a cell, recognizable components such as the nucleus, mitochondria, lysosomes, and the Golgi apparatus are characterized by distinct shapes and are enclosed in membranes. However, the focus of Dr. Mayr’s recent study involves two essential components that lack membranes, posing a challenge to their identification and laboratory investigation.
To delve into the intricacies of protein synthesis, a brief biological review outlines the process wherein DNA sequences are transcribed into messenger RNA (mRNA) within the cell nucleus. Subsequently, these mRNA molecules traverse into the cytoplasm, where they undergo translation to ultimately give rise to functional proteins.
The study’s significant revelation revolves around the non-random nature of the cytoplasm’s translation step, indicating an underlying logic or “code” that directs mRNAs to specific cellular neighborhoods. Dr. Mayr underscores the cytoplasm’s sophisticated compartmentalization, and the study successfully illustrates the existence of a code contingent upon the biophysical features of mRNAs—such as size and shape—and their interactions with specific RNA-binding proteins. This code functions as a guiding mechanism, directing mRNAs to distinct locations within the cell for the crucial translation process. This newfound understanding of the cellular organization adds a layer of complexity to the previously perceived “jumble” of components within the cytoplasm, highlighting its intricately organized nature. The implications extend beyond fundamental cellular biology, holding promise for potential applications in optimizing protein production in the context of mRNA-based vaccines and therapies.
Exploring cellular translation across three distinct locations
The research team, through a meticulous series of experiments, demonstrated that messenger RNAs (mRNAs) with different lengths and shapes exhibit a tendency to congregate in specific cellular neighborhoods. Intervening to redirect these mRNAs to alternative locations was found to exert a profound influence on both the quantity of produced proteins and the functionality of these proteins.
The focus of the investigation was on mRNAs situated on the surface of the endoplasmic reticulum (ER), an organelle integral to protein synthesis and various cellular functions. Established knowledge indicates that proteins associated with cellular membranes and those intended for secretion are typically translated at the ER. The study unveiled a noteworthy observation: approximately 15% of mRNAs encoding non-membrane proteins were also undergoing translation at the ER. Intriguingly, these mRNAs encoded large and highly expressed proteins.
Conversely, mRNAs translated in the cytosol, the liquid component of the cytoplasm, tended to encode very small proteins. Additionally, mRNAs located within Translation Initiation Site (TIS) granules, a membrane-less cellular component discovered by Dr. Mayr’s lab in 2018, were identified as primarily encoding transcription factors—proteins responsible for regulating gene transcription. TIS granules form a network of interconnected proteins and mRNAs and are closely associated with the endoplasmic reticulum, creating a distinct space for the collection and interaction of mRNA and proteins.
A striking visualization of the cell, captured through fluorescent microscopy, highlights TIS granules in red, while the endoplasmic reticulum is depicted in green. The nucleus of the cell is represented by the central black area. The findings contribute significantly to unraveling the intricate organization of cellular components within the cytoplasm and its impact on protein synthesis and function. This knowledge not only deepens our understanding of fundamental cellular processes but also holds potential implications for optimizing protein production in mRNA-based vaccines and therapies.
Deciphering the cipher
Unveiling the intricacies of mRNA localization within different cellular regions has brought forth unexpected revelations. Following the discovery of the TIS granule network five years ago, the research focused on identifying which of the numerous mRNAs in a cell localize to this network and whether they share common characteristics. The study zeroed in on a typically overlooked portion of the mRNA—the tail, specifically the three prime untranslated region (3′ UTR). While the tail has a longer sequence than the protein-building portion of the mRNA, it has historically received less attention.
Despite its conventional neglect, the tail was found to be crucial for forming partnerships with RNA-binding proteins, facilitating the mRNA’s correct localization within the cell for translation. RNA-binding proteins attach to RNA molecules and can modulate various aspects of their activity. Initially, researchers believed that these RNA-binding proteins played the primary role in directing the mRNA to specific locations within the cell.
However, a surprising discovery emerged: RNA-binding proteins actually play a secondary role rather than a primary one in the process. The default sorting of mRNA to specific locations is primarily based on the overall size and shape of the mRNAs. Yet, the presence of a binding protein can override this default, redirecting the mRNA to different locations.
The research team found that the translation of an mRNA in the TIS granules results in a protein with one function, while translation outside of the TIS granules leads to a protein with a different function. This insight highlights how, in higher organisms like humans, a single protein can serve multiple functions, providing a deeper understanding of the complex orchestration of cellular processes. Moreover, these findings carry implications for the optimization of protein production in mRNA-based vaccines and therapies.
Heading towards future applications
The study delved into the examination of specific proteins, with a notable focus on the MYC protein. The MYC gene is recognized as one of the prominent oncogenes, with mutations in MYC being implicated in the development of numerous cancers. The research uncovered that several MYC protein complexes were exclusively formed when the MYC mRNA underwent translation in the TIS granules, as opposed to translation in the cytosol.
This revelation holds crucial biological significance, particularly given that only around 20% of mRNAs undergo translation in the TIS granules. The findings suggest that targeting mRNA could be a strategic approach to achieve distinct functions and vary the production levels of specific proteins. The implications extend to the potential development of more sophisticated medicines in the future, allowing for the modulation of protein quantity and function. While the practical application of these insights may not manifest in the immediate future, the research lays the groundwork for future advancements in precision medicine.
Resources
- ONLINE NEWS Demsky, I. & Memorial Sloan Kettering Cancer Center. (2023, December 21). Location, location, location: Research reveals the hidden power of intracellular neighborhoods. Phys.org. [Phys.org]
- JOURNAL Horste, E. L., Fansler, M. M., Cai, T., Lee, F. C. Y., Ule, J., & Mayr, C. (2023). Subcytoplasmic location of translation controls protein output. Molecular Cell, 83(24), 4509-4523.e11. [Molecular Cell]
Cite this page:
APA 7: TWs Editor. (2023, December 22). A Novel Insight into Cell Biology: How Intracellular Neighborhoods Shape Cellular Outcomes? PerEXP Teamworks. [News Link]
