Posts Tagged ‘RNA alignment’

RNA in synthetic biology

Larry H. Bernstein, MD, FCAP, Curator



RNA May Surpass DNA in Precision Medicine


Scientists based at the Translational Genomics Research Institute have published a review heralding the promise of RNA sequencing (RNA-seq) for precision medicine. The scientists also note that progress will be needed on analytical, bioinformatics, and regulatory fronts, particularly in light of the transcriptome’s variety, dynamism, and wealth of detail. In this image, one aspect of RNA-seq is shown, the alignment with intron-split short reads. It reflects the alignment of mRNA sequence obtained via high-throughput sequencing and the expected behavior of the alignment to the reference genome when the read falls in an exon–exon junction. [Rgocs, Wikipedia]


It’s not an either/or situation. Both DNA sequencing and RNA sequencing hold clinical promise—diagnostically, prognostically, and therapeutically. It must be said, however, that RNA sequencing reflects the dynamic nature of gene expression, shifting with the vagaries of health and disease. Also, RNA sequencing captures more biochemical complexity, in the sense that it allows for the detection of a wide variety of RNA species, including mRNA, noncoding RNA, pathogen RNA, chimeric gene fusions, transcript isoforms, and splice variants, and provides the capability to quantify known, predefined RNA species and rare RNA transcript variants within a sample.

All these potential advantages were cited in a paper that appeared March 21 in Nature Reviews Genetics, in an article entitled, “Translating RNA Sequencing into Clinical Diagnostics: Opportunities and Challenges.” The paper, contributed by scientists based at the Translational Genomics Research Institute (TGen), was definitely optimistic about the clinical utility of RNA sequencing, but it also highlighted the advances that would have to occur if RNA sequencing is to achieve its promise.

In general, the very things that make RNA sequencing so interesting are the same things that make it so challenging. RNA sequencing would take the measure of a world—the transcriptome—that is incredibly rich. To capture all the relevant subtleties of the transcriptome, scientists will have to develop sensitive, precise, and trustworthy analytical techniques. What’s more, scientists will need to find efficient and reliable means of processing and interpreting all of the transcriptome data they will collect. Finally, they will need to continue integrating RNA-based knowledge with DNA-based knowledge. That is, RNA sequencing results can be used to guide the interpretation of DNA sequencing results.

In their Nature Reviews Genetics paper, the TGen scientists review the state of RNA sequencing and offer specific recommendations to enhance its clinical utility. The TGen scientists make a special point about the promise held by extracellular RNA (exRNA). Because exRNA can be monitored by simply taking a blood sample, as opposed to taking a tumor biopsy, it could serve as a noninvasive diagnostic indicator of disease.

“Detection of gene fusions and differential expression of known disease-causing transcripts by RNA-seq represent some of the most immediate opportunities,” wrote the authors. “However, it is the diversity of RNA species detected through RNA-seq that holds new promise for the multi-faceted clinical applicability of RNA-based measures, including the potential of extracellular RNAs as non-invasive diagnostic indicators of disease.”

The first test measuring exRNA was released earlier this year, the paper said, for use measuring specific exRNAs in lung cancer patients. And, the potential for using RNA-seq in cancer is expanding rapidly. Commercial RNA-seq tests are now available, and they provide the opportunity for clinicians to profile cancer more comprehensively and use this information to guide treatment selection for their patients.

In addition, the authors reported on several recent applications for RNA-seq in the diagnosis and management of infectious diseases, such as monitoring for drug-resistant populations during therapy and tracking the origin and spread of the Ebola virus.

Despite these advances, the authors also sounded a few cautionary notes. “There are currently few agreed upon methods for isolation or quantitative measurements and a current lack of quality controls that can be used to test platform accuracy and sample preparation quality,” they wrote. “Analytical, bioinformatics, and regulatory challenges exist, and ongoing efforts toward the establishment of benchmark standards, assay optimization for clinical conditions and demonstration of assay reproducibility are required to expand the clinical utility of RNA-seq.”

Overall, the authors remain hopeful that precision medicine will embrace RNA sequencing. For example, lead author Sara Byron, research assistant professor in TGen’s Center for Translational Innovation, said, “RNA is a dynamic and diverse biomolecule with an essential role in numerous biological processes. From a molecular diagnostic standpoint, RNA-based measurements have the potential for broad application across diverse areas of human health, including disease diagnosis, prognosis, and therapeutic selection.”


RNA Bacteriophages May Open New Path to Fighting Antibiotic-Resistant Infections

Micrograph image of RNA bacteriophages attached to part of the bacterium E. coli. A new study at Washington University School of Medicine in St. Louis suggests that bacteriophages made of RNA, a close chemical cousin of DNA, likely play a much larger role in shaping the bacterial makeup of worldwide habitats than previously recognized. [Graham Beards/Wikimedia]

Scientists at Washington University School of Medicine in St. Louis report that bacteriophages made of RNA likely play a much larger role in shaping the bacterial makeup of worldwide habitats than previously recognized. Their study (“Hyperexpansion of RNA Bacteriophage Diversity”), published in PLOS Biology, identified 122 new types of RNA bacteriophages in diverse ecological niches, providing an opportunity for scientists to define their contributions to ecology and potentially to exploit them as novel tools to fight bacterial infections, particularly those that are resistant to antibiotics.

“Lots of DNA bacteriophages have been identified, but there’s an incredible lack of understanding about RNA bacteriophages,” explained senior author David Wang, Ph.D., associate professor of molecular microbiology. “They have been largely ignored—relatively few were known to exist, and for the most part, scientists haven’t bothered to look for them. This study puts RNA bacteriophages on the map and opens many new avenues of exploration.”

Dr. Wang estimates that of the more than 1500 bacteriophages that have been identified, 99% of them have DNA genomes. The advent of large-scale genome sequencing has helped scientists identify DNA bacteriophages in the human gut, skin, and blood, as well as in the environment, but few researchers have looked for RNA bacteriophages in those samples (doing so requires that RNA be isolated from the samples and then converted back to DNA before sequencing).

As part of the new study, first author and graduate student Siddharth Krishnamurthy, and the team, including Dan Barouch, M.D., Ph.D., of Beth Israel Deaconess Medical Center and Harvard Medical School, identified RNA bacteriophages by analyzing data from samples taken from the environment, such as oceans, sewage, and soils, and from aquatic invertebrates including crabs, sponges, and barnacles, as well as insects, mice, and rhesus macaques.

RNA bacteriophages have been shown to infect Gram-negative bacteria, which have become increasingly resistant to antibiotics and are the source of many infections in health care settings. But the researchers also showed for the first time that these bacteriophages also may infect Gram-positive bacteria, which are responsible for strep and staph infections as well as MRSA (methicillin-resistant Staphylococcus aureus).

“What we know about RNA bacteriophages in any environment is limited,” Dr. Wang said. “But you can think of bacteriophages and bacteria as having a predator–prey relationship. We need to understand the dynamics of that relationship. Eventually, we’d like to manipulate that dynamic to use phages to selectively kill particular bacteria.”


Hyperexpansion of RNA Bacteriophage Diversity

Siddharth R. Krishnamurthy , Andrew B. Janowski , Guoyan Zhao , Dan Barouch
24 Mar 2016 | PLOS Biology

Bacteriophage modulation of microbial populations impacts critical processes in ocean, soil, and animal ecosystems. However, the role of bacteriophages with RNA genomes (RNA bacteriophages) in these processes is poorly understood, in part because of the limited number of known RNA bacteriophage species. Here, we identify partial genome sequences of 122 RNA bacteriophage phylotypes that are highly divergent from each other and from previously described RNA bacteriophages. These novel RNA bacteriophage sequences were present in samples collected from a range of ecological niches worldwide, including invertebrates and extreme microbial sediment, demonstrating that they are more widely distributed than previously recognized. Genomic analyses of these novel bacteriophages yielded multiple novel genome organizations. Furthermore, one RNA bacteriophage was detected in the transcriptome of a pure culture of Streptomyces avermitilis, suggesting for the first time that the known tropism of RNA bacteriophages may include gram-positive bacteria. Finally, reverse transcription PCR (RT-PCR)-based screening for two specific RNA bacteriophages in stool samples from a longitudinal cohort of macaques suggested that they are generally acutely present rather than persistent.

Bacteriophages (viruses that infect bacteria) can alter biological processes in numerous ecosystems. While there are numerous studies describing the role of bacteriophages with DNA genomes in these processes, the role of bacteriophages with RNA genomes (RNA bacteriophages) is poorly understood. This gap in knowledge is in part because of the limited diversity of known RNA bacteriophages. Here, we begin to address the question by identifying 122 novel RNA bacteriophage partial genome sequences present in metagenomic datasets that are highly divergent from each other and previously described RNA bacteriophages. Additionally, many of these sequences contained novel properties, including novel genes, segmentation, and host range, expanding the frontiers of RNA bacteriophage genomics, evolution, and tropism. These novel RNA bacteriophage sequences were globally distributed from numerous ecological niches, including animal-associated and environmental habitats. These findings will facilitate our understanding of the role of the RNA bacteriophage in microbial communities. Furthermore, there are likely many more unrecognized RNA bacteriophages that remain to be discovered.



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