Many biological processes can not be fully understood without detailed knowledge of RNA metabolism. RNA does more than simply serve an intermediary function and many RNA molecules are the principal actors in largely unexplored networks of gene regulation. RNA is full of surprises and in 2006 two Nobel prizes were attributed in the field of RNA. Unknown classes of noncoding RNAs have been discovered. MicroRNAs (miRNA) and small interfering RNAs (siRNA) have been shown to bind and control their target mRNAs. Chemically synthesized siRNA are showing to be a ground-breaking tool for analysis of gene function and gene therapy.

RNA stability is very important for differential gene expression. RNAs differ in their susceptibility to degradation by ribonucleases, due in part to their different sequence and structure. Moreover, there are surveillance mechanisms that degrade aberrant RNAs. Mutants deficient in one or more ribonucleases have played a primordial role in the study of the decay processes. The rates of decay can be altered in response to stress and physiological signals. RNA metabolism shows greater similarities between prokaryotic and eukaryotic systems than was generally believed. For instance, in both systems poly(A) tails of mRNAs play major roles in the control of mRNA decay. It is important to study RNA metabolism in different systems, to allow universally conserved features to be recognized.

The maturation, turnover and quality control of RNA is performed by many different classes of ribonucleases. Ribonuclease II (RNase II) intervenes in all of these fundamental processes, degrading single-stranded RNA from its 3' end and releasing ribonucleoside 5'-monophosphates. This exoribonuclease can act independently or as a component of the exosome, an essential RNA-degrading multiprotein complex. RNase II-like enzymes are found in all three domains of life. RNase II is often essential for growth, can be developmentally regulated, and mutations in its gene have been linked with abnormal chloroplast biogenesis, mitotic control and cancer.

We have participated in the resolution of the structures of both the ligand-free and RNA-bound forms of Escherichia coli RNase II. The structural and biochemical analysis has helped explaining the activity of these enzymes. The 3D model proposed showed the dynamics of the RNase II-mediated RNA degradation and opened an exciting new chapter in the comprehension of RNA metabolism. We have constructed mutants of RNase II protein and RNase II-hybrid proteins with domains from other exoribonucleases. We have confirmed the role of specific aminoacids, we have identified the residue responsible for setting the end product, and we have constructed a “super-enzyme”. Computational analysis has given interesting data regarding the evolution of the RNase II family of enzymes. In particular we are focusing our studies in the enzymes that have been crucial in defining the properties of the exosome (namely the Rrp44 /Dis3 yeast and human homologues), in enzymes that we have already been studying (namely E. coli RNase R and Drosophila Tazman), and enzymes that can be important in pathogenesis (RNase II from Salmonella thyphimurium and Streptococcus pneumoniae). We have also constructed mutants to study the role of RNase II in the degradation of mRNAs and small noncoding RNAs. We also want to understand its role in the surveillance mechanisms that degrade aberrant RNAs for RNA quality control. The biological significance of the RNase II family of enzymes will be discussed.

TBA

The promise of genomic medicine includes personalizing diagnoses and therapies, if not to the level of the individual, then to a small population of individuals with shared pathophysiology. The availability of commodity-priced genome-scale assays has led to increased popular demand and expectation for the application of these assays to clinical care. Yet there are several structural impediments to the safe practice of genomic medicine, all of which fall within the domain of biomedical informatics. These include:

1. the growth of the Incidentalome, the tsunami of false positives that inevitably result from application of massively parallel tests;
2. the lack of systematic interpretations of genomic tests and evaluation of their performance;
3. the absence of a mechanism to transfer the growing knowledge of genomics to the physician at the point of care.

Fortunately there are several developments in biomedical informatics that address these impediments. These include:

1. the industrialization of measurement of phenotype, sample acquisition and genotype across large populations seen in the course of clinical care as exemplified by the i2b2 infrastructure (see www.i2b2.org);
2. integration of knowledge from the bibliome into clinical care;
3. including patients as collaborators in the research enterprise.

Helicos Single Molecule Sequencing provides a unique view of genome biology through direct sequencing of cellular nucleic acids in an unbiased manner providing both quantitation and sequence information. Using a simple sample preparation involving no ligation or PCR amplification genomic DNA is sheared, tailed with poly A and hybridized to the flow cell surface containing oligo-dT for initiating sequencing by synthesis. RNA measurements include both single stranded cDNA based measurements as well as new studies which rely on direct hybridization of RNA to the flow cell to directly sequence and quantitate RNA molecules. From these methods a diverse array of applications have now be successfully demonstrated on the HeliScopeTM Sequencer including human genome sequencing for accurate variant detection, ChIP Seq studies involving picogram quantities of DNA obtained from low cell quantities, copy number variation studies from both fresh tumor tissue and formalin-fixed paraffin embedded tissue and archival tissue samples, the study of ancient and degraded DNAs, small RNA studies leading to the identification of new classes of RNAs and the direct capture and sequencing of RNA from cell quantities as low as 200 cells. We continue to optimize our sample preparation protocols to allow preparation and sequencing from picogram quantities of nucleic acid – all aimed at maximizing researchers ability to perform important biological experiments with limiting biological sample amounts. Genomic studies aimed at building comprehensive views of cellular states including tumor biological differences will be discussed.

We are using high-throughput genome-wide RNA interference (RNAi) screens to assign phenotypic signatures, or phenoprints, to every gene in the fruit fly Drosophila melanogaster. These screens are based on a diverse set of cell-based assays, which rely on transcriptional analyses, protein modification, and high-content imaging to provide a wealth of phenotypic information. With these phenoprints, global correlations can be drawn to other large-scale datasets, such as transcriptional profiling and interactome data, in order to derive the network graphs critical for data mining. In addition, our group is taking a quantitative approach to elucidate the organization of signaling networks, using a combination of RNAi, gene expression profiling and Mass Spectrometry approaches.

Large-scale cellular networks have been determined for a wide range of organisms across the evolutionary spectrum. Computational analyses of these networks have proven to be an important means for uncovering insights into cellular organization and functioning. The next frontier in biological network analysis is the development of approaches for inferring the dynamics inherent within known networks. Indeed, proper cellular functioning requires the precise coordination of a large number of events, and dynamic molecular interactions play a central role in regulating the functioning of cells and organisms. Thus, identifying the temporal and contextual signals underlying proposed interactions is a crucial part of understanding cellular function. In this talk, I will highlight recent computational efforts attempting to characterize dynamics from large-scale biological networks, and suggest promising avenues for future work.