Synthetic mRNA-Based Systems in Mammalian Cells

The advent of clinical self-amplifying RNA vaccines

Self-amplifying RNA (saRNA) technology is an emerging platform for vaccine development, offering significant advantages over conventional mRNA vaccines. By enabling intracellular amplification of RNA, saRNA facilitates robust antigen expression at lower doses, thereby enhancing both immunogenicity and cost-effectiveness. This review examines the latest advancements in saRNA vaccine development, highlighting its applications in combating infectious diseases. This includes viral pathogens such as SARS-CoV-2, influenza, and emerging zoonotic threats. We discuss the design and optimization of saRNA vectors to maximize antigen expression while minimizing adverse immune responses. Recent studies demonstrating the safety, efficacy, and scalability of saRNA-based vaccines in clinical settings are also discussed. We address challenges related to delivery systems, stability, and manufacturing, along with novel strategies being developed to mitigate these challenges. As the global demand for rapid, flexible, and scalable vaccine platforms grows, saRNA presents a promising solution with enhanced potency and durability. This review emphasizes the transformative potential of saRNA vaccines to shape the future of immunization strategies, particularly in response to pandemics and other global health threats.

Recent Advances in the miRNA-Mediated Regulation of Neuronal Differentiation and Death

The review aims to focus on the role of miRNA in gene regulation, related to differentiation and apoptosis of neurons, focusing on the array of miRNAs involved in the processes. miRNAs are a known class of small regulatory RNAs, which in association with RNA processing bodies, play major roles in different cellular events, such as neurogenesis and neuronal differentiation. miRNAs function in controlling neuronal events by targeting different important molecules of cellular signalling. The post-translational modification of Ago2 is crucial in modulating the neurons' miRNA-mediated regulation. Thus, understanding the crosstalk between cellular signalling and miRNA activity affecting neuronal events is very important to decipher novel targets and related signalling pathways, involved in neuronal survival and neurodegeneration.

Cytidine-containing tails robustly enhance and prolong protein production of synthetic mRNA in cell and in vivo

Synthetic mRNAs are rising rapidly as alternative therapeutic agents for delivery of proteins. However, the practical use of synthetic mRNAs has been restricted by their low cellular stability as well as poor protein production efficiency. The key roles of poly(A) tail on mRNA biology inspire us to explore the optimization of tail sequence to overcome the aforementioned limitations. Here, the systematic substitution of non-A nucleotides in the tails revealed that cytidine-containing tails can substantially enhance the protein production rate and duration of synthetic mRNAs both in vitro and in vivo. Such C-containing tails shield synthetic mRNAs from deadenylase CCR4-NOT transcription complex, as the catalytic CNOT proteins, especially CNOT6L and CNOT7, have lower efficiency in trimming of cytidine. Consistently, these enhancement effects of C-containing tails were observed on all synthetic mRNAs tested and were independent of transfection reagents and cell types. As the C-containing tails can be used along with other mRNA enhancement technologies to synergically boost protein production, we believe that these tails can be broadly used on synthetic mRNAs to directly promote their clinical applications.

Purification of human iPSC-derived cells at large scale using microRNA switch and magnetic-activated cell sorting

For regenerative cell therapies using pluripotent stem cell (PSC)-derived cells, large quantities of purified cells are required. Magnetic-activated cell sorting (MACS) is a powerful approach to collect target antigen-positive cells; however, it remains a challenge to purify various cell types efficiently at large scale without using antibodies specific to the desired cell type. Here we develop a technology that combines microRNA (miRNA)-responsive mRNA switch (miR-switch) with MACS (miR-switch-MACS) to purify large amounts of PSC-derived cells rapidly and effectively. We designed miR-switches that detect specific miRNAs expressed in target cells and controlled the translation of a CD4-coding transgene as a selection marker for MACS. For the large-scale purification of induced PSC-derived cardiomyocytes (iPSC-CMs), we transferred miR-208a-CD4 switch-MACS and obtained purified iPSC-CMs efficiently. Moreover, miR-375-CD4 switch-MACS highly purified pancreatic insulin-producing cells and their progenitors expressing Chromogranin A. Overall, the miR-switch-MACS method can efficiently purify target PSC-derived cells for cell replacement therapy.

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MiR-208a-CD4 switch-MACS can purify a large amount of iPSC-CMs in a short time

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MiR-208a switch can purify iPSC-CMs in each subtype-specific protocol

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MiR-375-CD4 switch-MACS can be applied to pancreatic endocrine precursor cells

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MiR-switch-MACS method can be efficient for large-scale target cell purification

An RNA Triangle with Six Ribozyme Units Can Promote a Trans-Splicing Reaction through Trimerization of Unit Ribozyme Dimers

Ribozymes are catalytic RNAs that are attractive platforms for the construction of nanoscale objects with biological functions. We designed a dimeric form of the Tetrahymena group I ribozyme as a unit structure in which two ribozymes were connected in a tail-to-tail manner with a linker element. We introduced a kink-turn motif as a bent linker element of the ribozyme dimer to design a closed trimer with a triangular shape. The oligomeric states of the resulting ribozyme dimers (kUrds) were analyzed biochemically and observed directly by atomic force microscopy (AFM). Formation of kUrd oligomers also triggered trans-splicing reactions, which could be monitored with a reporter system to yield a fluorescent RNA aptamer as the trans-splicing product.