RNA interference and mRNA silencing, 2004: how far will they reach?

Introns and Their Therapeutic Applications in Biomedical Researches

Context

Although for a long time, it was thought that intervening sequences (introns) were junk DNA without any function, their critical roles and the underlying molecular mechanisms in genome regulation have only recently come to light. Introns not only carry information for splicing, but they also play many supportive roles in gene regulation at different levels. They are supposed to function as useful tools in various biological processes, particularly in the diagnosis and treatment of diseases. Introns can contribute to numerous biological processes, including gene silencing, gene imprinting, transcription, mRNA metabolism, mRNA nuclear export, mRNA localization, mRNA surveillance, RNA editing, NMD, translation, protein stability, ribosome biogenesis, cell growth, embryonic development, apoptosis, molecular evolution, genome expansion, and proteome diversity through various mechanisms.

Evidence Acquisition

In order to fulfill the objectives of this study, the following databases were searched: Medline, Scopus, Web of Science, EBSCO, Open Access Journals, and Google Scholar. Only articles published in English were included.

Results & Conclusions

The intervening sequences of eukaryotic genes have critical functions in genome regulation, as well as in molecular evolution. Here, we summarize recent advances in our understanding of how introns influence genome regulation, as well as their effects on molecular evolution. Moreover, therapeutic strategies based on intron sequences are discussed. According to the obtained results, a thorough understanding of intron functional mechanisms could lead to new opportunities in disease diagnosis and therapies, as well as in biotechnology applications.

Therapeutic potential of a combination of two gene-specific small interfering RNAs against clinical strains of Acanthamoeba

Pathogenic strains of the genus Acanthamoeba are causative agents of severe infections, such as fatal encephalitis and a sight-threatening amoebic keratitis. Antimicrobial therapy for these infections is generally empirical, and patient recovery is often problematic, due to the existence of a highly resistant cyst stage in these amoebae. In previous studies, small interfering RNAs (siRNAs) against the catalytic domains of extracellular serine proteases and glycogen phosphorylase from Acanthamoeba were designed and evaluated for future therapeutic use. The silencing of proteases resulted in Acanthamoeba failing to degrade human corneal cells, and silencing of glycogen phosphorylase caused amoebae to be unable to form mature cysts. After the siRNA design and concentration were optimized in order to avoid toxicity problems, cultures of Acanthamoeba were treated with a combination of both siRNAs, and cells were evaluated under an inverted microscope. This siRNA-based treatment dramatically affected the growth rate and cellular survival of the amoebae. These results were observed less than 48 h after the initiation of the treatment. In order to check possible toxic effects of the siRNA combination, three eukaryotic cell lines (HeLa, murine macrophages, and osteosarcoma cells) were treated with the same molecules, and cytotoxicity was examined by measuring lactate dehydrogenase release. The future use of the combination of these siRNAs is proposed as a potential therapeutic approach against pathogenic strains of Acanthamoeba.

Intronic microRNAs

MicroRNAs (miRNAs), small single-stranded regulatory RNAs capable of interfering with intracellular mRNAs that contain partial complementarity, are useful for the design of new therapies against cancer polymorphism and viral mutation. MiRNA was originally discovered in the intergenic regions of the Caenorhabditis elegans genome as native RNA fragments that modulate a wide range of genetic regulatory pathways during animal development. However, neither RNA promoter nor polymerase responsible for miRNA biogenesis was determined. Recent findings of intron-derived miRNA in C. elegans, mouse, and human have inevitably led to an alternative pathway for miRNA biogenesis, which relies on the coupled interaction of Pol-II-mediated pre-mRNA transcription and intron excision, occurring in certain nuclear regions proximal to genomic perichromatin fibrils.

Intron-derived microRNAs--fine tuning of gene functions

New evidence suggests that abundant small RNAs, microRNAs (miRNAs) act as regulatory vehicles to repress translation or cleave RNA transcripts, depending on their complementarity to the target gene, and result in modulation of gene expression. This review describes that the miRNAs derived from introns can suppress intracellular RNA homologues and regulate the gene function.

Post-transcriptional gene silencing in neurons

The techniques evolving from the rapidly developing field of small RNAs promise accessible approaches to dissecting cellular and molecular mechanisms of higher brain function. Here, a current overview of the technology is presented, along with an outline of how these approaches might help neuroscientists to more rapidly uncover the cellular and molecular bases of behavior.