🧬 PubMed RNA Editing Daily Digest

Reprogrammable Adenosine Deaminase Acting on RNA (ADAR) Sensors (RADARS) control RNA translation in mammalian cells, allowing for noninvasive sensing or perturbation of specific cell types based on transcriptional signatures. Upon base-pairing between a target RNA and a sensor RNA, RADARS leverages ADAR to edit a premature stop codon upstream of a gene of interest, thereby releasing translation of the desired cargo. These design principles enable sequence programmability, allowing RADARS to adapt more easily to new contexts than existing tools for targeting cell types. We describe a detailed protocol for performing experiments with RADARS, including designing, cloning and validating RADARS constructs targeting a transcript of interest. RADARS guide sequences can be designed with an intuitive web interface and cloned into existing constructs for downstream applications including imaging, sorting and sequencing. We outline recommendations for cargo choice, sensor design and ADAR system selection, enabling users to choose the best workflow depending on the desired application. Beginning with sensor design, the selection of top-performing RADARS guides can be completed in ~2 weeks, followed by a desired use case. Convenient engineering and application of RADARS for various applications enable the design and execution of various cell-targeting experiments.

Acute lung injury (ALI) is characterized by a considerable mortality rate and currently lacks viable therapeutic strategies. Alveolar type II epithelial cells (AT2 cells) play a critical role in lung injury repair, potentially through activation of the Wnt/β-catenin signaling cascade, which may enhance regenerative ability of lung tissue. In this study, we developed a mini-catalytically inactive Cas13X (mini dCas13X)-based adenosine-to-inosine (A-to-I) RNA editing approach, designated as β-

Cytosine base editors (CBEs) and adenine base editors (ABEs) are powerful tools for precise genome editing in plants. Conventionally, such base editors are built upon the CRISPR-Cas9 systems where Cas9 nickases are used. To expand the base editing scope and minimize off-target effects, base editors derived from the CRISPR-Cas12a systems are desired. However, the use of deactivated Cas12a (dCas12a) in such base editors constrains the editing activity, preventing the wide use of Cas12a base editors for plant research and trait development. In this study, we demonstrate the use of an ABE based on the efficient LbCas12a-RRV variant to introduce herbicide-resistant mutations in OsACCase in rice. To improve Cas12a CBEs and ABEs, we inserted introns into the coding sequence of dLbCas12a-RRV. This intron-containing Cas12a-CBE shows substantial improvement in editing efficiency in rice, compared to the non-intron counterparts. By contrast, the improvement of ABE with the intron-containing dLbCas12a-RRV is very limited, partly due to the already high baseline editing efficiency of the intron-less dLbCas12a-RRV ABE. Testing of these base editors in poplar shows elevated C-to-T base editing by dLbCas12a-RRV-intron-CBE. For A-to-G editing, ABEs built upon dLbCas12a-RV and dLbCas12a-RRV variants showed significant improvement over ABEs derived from wild-type LbCas12a and the ttLbCas12a variant. The addition of introns to dLbCas12a-RRV does not further improve the base editing efficiency. With whole genome sequencing in rice, we evaluated genome editing specificities with these improved Cas12a base editors. Our analyses show that both intron-containing Cas12a CBE and ABE barely introduce guide RNA-dependent off-target mutations. However, they can generate guide RNA-independent off-target mutations, which are likely attributed to the high enzymatic activities of the deaminases. Collectively, our study demonstrates the successful use of a Cas12a base editor for trait development and reports improved Cas12a CBEs and ABEs for precise base editing in plants.

Adenosine-to-inosine (A-to-I) mRNA editing alters genetic information post-transcriptionally and can impact protein sequence and function, yet its regulation in bacteria remains unclear. Here, we profiled A-to-I editing in

CRISPR RNAs (crRNAs) guide recognition and targeting of intracellular invaders as part of adaptive immunity by CRISPR-Cas systems. crRNAs are transcribed from CRISPR arrays of conserved repeats interlaced with invader-derived spacers. While crRNA production is essential for immunity, its optimization for defense remains poorly understood. Here, we show that, in diverse RNA-targeting type VI CRISPR-Cas systems, the leader RNA encoded upstream of the CRISPR array prevents formation of an invader-independent extraneous crRNA (ecrRNA) by blocking processing of the first repeat. Using the VI-B2 system from Porphyromonas gingivalis as a model, we demonstrate that the leader RNA and first repeat form a conserved inhibitory hairpin that precludes binding and processing by the system's Cas13b nuclease. Disrupting this hairpin enables ecrRNA production, which in turn can deplete invader-derived crRNAs and reduce Cas13b-mediated phage defense. Structure prediction indicates that these leader-repeat hairpins are widespread across diverse type VI subtypes, highlighting a conserved regulatory mechanism. Our findings reveal how a prevalent branch of CRISPR-Cas systems suppresses ecrRNA formation to promote RNA-guided immunity.