GO:0070878 primary miRNA binding: Mechanism, Genes

Primary miRNA binding (GO:0070878) is a biological process defined as the selective interaction of RNA-binding proteins with primary microRNA (pri-miRNA) transcripts, the long capped and polyadenylated precursors of microRNAs. This binding event is the first committed step in the canonical microRNA biogenesis pathway and determines which transcripts are recognized for subsequent processing. In animals, the Microprocessor complex, minimally composed of the RNase III enzyme Drosha and its partner DGCR8, binds pri-miRNAs and cleaves them into precursor miRNAs (pre-miRNAs). In plants and algae, homologous but distinct protein factors, such as DUS16 in Chlamydomonas reinhardtii, carry out the primary miRNA binding and processing functions. The process is highly regulated, with accessory proteins like SERRATE contributing to phase separation and m6A modification that influence binding and processing efficiency. Researchers study primary miRNA binding because it sits at the nexus of gene regulation by small RNAs. Defects in this step alter the repertoire of mature miRNAs, leading to widespread changes in target gene expression. For example, Tankyrase has been shown to promote primary precursor miRNA processing to precursor miRNA, highlighting the role of additional factors in modulating this binding event. Moreover, noncanonical processing pathways in animals can bypass typical Microprocessor requirements, underscoring the diversity of primary miRNA binding mechanisms. Clinically, mutations or dysregulation affecting primary miRNA binding have been implicated in rare human diseases and in cancer progression, such as the hsa-miR-9-FABP7 axis in triple-negative breast cancer. Thus, understanding GO:0070878 provides mechanistic insight into miRNA biology and offers potential therapeutic entry points. The importance of primary miRNA binding extends to biotechnology and medicine. Exosomal sorting of cargo, including RNA-binding proteins like RBMX, is regulated by SUMOylation and can impact miRNA loading and function. Delivery systems for miRNAs, such as tetrahedral framework DNA-based systems, rely on efficient intracellular processing that begins with primary miRNA binding. Therefore, this GO term is central to both fundamental RNA biology and translational applications.

Primary miRNA binding (GO:0070878) is the biological process in which a protein or protein complex selectively interacts with a primary microRNA (pri-miRNA) transcript. This binding event is a prerequisite for the subsequent endonucleolytic cleavage that generates precursor miRNA (pre-miRNA) and eventually mature miRNA. The process is mediated by dedicated RNA-binding proteins, such as DUS16 in algae and the Microprocessor complex in animals, and can be regulated by post-translational modifications and phase separation.

Primary miRNA binding is a critical control point in microRNA biogenesis because it determines which pri-miRNA transcripts are selected for processing and how efficiently they are converted into mature miRNAs. This process influences a vast network of downstream gene expression programs, and its dysregulation has been linked to human diseases ranging from rare genetic disorders to cancer. Understanding the molecular players and regulatory mechanisms of primary miRNA binding can reveal therapeutic targets and guide the development of RNA-based therapeutics.

The following genes and proteins have been experimentally implicated in primary miRNA binding (GO:0070878) or in the processing steps immediately downstream of this binding event.

Primary miRNA binding is regulated at multiple levels. Post-translational modifications, such as SUMOylation and DeSUMOylation, control the activity and localization of RNA-binding proteins like RBMX, which in turn affects exosomal cargo sorting and miRNA processing. Phase separation of SERRATE regulates m6A modification and miRNA biogenesis, indicating that condensate formation can modulate primary miRNA binding efficiency. Additionally, factors such as Tankyrase can promote the processing of primary precursor miRNA to precursor miRNA, suggesting a regulatory role in the cleavage step following binding. Noncanonical processing pathways also provide alternative regulatory routes that can bypass canonical Microprocessor components.

Mutations in genes encoding components of the miRNA biogenesis machinery, including those involved in primary miRNA binding, have been linked to rare human diseases. A review of microRNA and rare human diseases highlights that defects in miRNA processing can lead to developmental abnormalities and other clinical phenotypes. Although specific mutations in primary miRNA binding factors are still being catalogued, the pathway is recognized as a contributor to Mendelian disorders.

Dysregulation of primary miRNA binding can alter the expression of oncogenic or tumor-suppressive miRNAs. In triple-negative breast cancer, the hsa-miR-9-FABP7 axis has been identified as a predictive biomarker for metastatic progression, and the production of hsa-miR-9 depends on proper primary miRNA binding and processing. Therefore, factors that modulate primary miRNA binding may influence cancer progression and serve as therapeutic targets.

DeSUMOylation of RBMX regulates exosomal sorting of cargo and promotes renal tubulointerstitial fibrosis in diabetic kidney disease. This links primary miRNA binding-related proteins to the pathogenesis of fibrotic kidney disease, suggesting that miRNA processing and sorting pathways are relevant to metabolic complications.

Manipulating primary miRNA binding could enhance miRNA-based therapies. A bioswitchable miRNA delivery system based on tetrahedral framework DNA has been developed for wound healing applications, and its efficacy depends on intracellular processing that begins with primary miRNA binding. Thus, understanding and controlling primary miRNA binding may improve the design of miRNA therapeutics.

RNA immunoprecipitation (RIP) and crosslinking and immunoprecipitation (CLIP) are key methods to detect direct binding of proteins to pri-miRNAs. These techniques can be coupled with high-throughput sequencing to map binding sites at nucleotide resolution. They are essential for validating primary miRNA binding events and identifying novel pri-miRNA substrates.

Recombinant proteins or purified complexes can be incubated with radiolabeled or fluorescently labeled pri-miRNA transcripts to measure binding affinity and cleavage activity. Such assays have been used to study Microprocessor function and the role of accessory factors like Tankyrase. They allow precise dissection of the biochemical requirements for primary miRNA binding.

Small RNA sequencing quantifies mature miRNA levels and can infer defects in primary miRNA binding when pri-miRNA processing is impaired. This approach has been used in studies of DUS16 and SERRATE to link binding factors to miRNA output. It is a standard readout for functional perturbations of the pathway.

Genome-wide CRISPR knockout or activation screens can identify genes that regulate primary miRNA binding and processing. Such screens have the power to uncover novel factors and pathways, complementing candidate-based studies. They are particularly useful for discovering noncanonical components.

Researchers studying primary miRNA binding-related genes often need to determine whether a candidate gene is causally involved in pri-miRNA recognition and processing. This requires precise genetic models that can knock out, mutate, tag, or overexpress the gene of interest in relevant cell types. EDITGENE provides a comprehensive suite of CRISPR services to enable such studies, from single-gene editing to genome-wide library screening and bioinformatics analysis.

Primary miRNA binding (GO:0070878) is a fundamental biological process that initiates the microRNA biogenesis pathway by recruiting specific RNA-binding proteins to pri-miRNA transcripts. Its regulation by post-translational modifications and phase separation ensures precise control of miRNA production, and its dysregulation contributes to human diseases including cancer and rare genetic disorders. Continued research using CRISPR-based models and advanced sequencing methods will further illuminate the molecular details and therapeutic potential of this process.