Gene expression

This project used a bioinformatics approach to identify the genetic differential expression of chronic lymphocytic leukemia (CLL) white blood cells as compared to normal white blood cells. Several public access databases and data mining tools were used to collect these data. The data collected was validated by independent bioinformatics databases and the methodology was supported by previously published "gene chip" differential expression data. This research identifies a pattern of differential gene expression specific to CLL white blood cells that can be used for the early diagnosis of CLL. The study also identifies the probable genetic origin for the low expression of tyrosine kinase and IgM immunoglobulin observed in CLL B-cells. Also presented are genes associated with chromosomal regions previously reported as deleted in a high percentage of CLL cases. These data can be used in further research and for the treatment of CLL.

It is known that Reovirus selectively destroys transformed cells, but the complex mechanism is not completely understood at this time. In this study, gene expression was examined by comparing Reovirus-infected SV-40 transformed human embryonic fibroblasts, with mock-infected cells. Among the 40 genes shown to be altered, 38 genes were up regulated, and 2 genes were down regulated. Out of the 40 genes having differential gene expression, 8 were significantly over induced. 3 of these were DNA binding transcription factors. Activation of transcription factors following Reovirus infection suggests that gene expression is essential in Reovirus induced transformed cell killing. Another 3 genes were found to be tumor suppressor proteins and oncogenes expressed downstream of the Ras pathway. The over expression of these was shown to induce apoptosis induced cell killing by Reovirus. Finally, 2 of the 8 significantly up regulated genes cause cell cycle progression inhibition. The cell cycle arrest then leads to cell death.

Recently Dr. Narayanan's laboratory, utilizing bioinformatics approaches, identified a novel gene which may play a role in colon cancer. This gene in view of its expression specificity was termed Colon Carcinoma Related Gene (CCRG). The CCRG belongs to a novel class of secreted molecules with a unique cysteine rich motif. The function of CCRG however, remains unknown. The basis of this project revolved around establishing the putative function (functional genomics) of CCRG. The rationale for the project was to test a hypothesis that CCRG may offer a growth advantage to cancer cells. The availability of diverse tumor-derived cell lines, which were CCRG negative offered a possibility to study the consequence of enforced expression of CCRG. A breast carcinoma cell line was transfected with an exogenous CCRG expression vector and the stable clones were characterized. The stable transfectants of CCRG showed enhanced growth and a partial abrogation of serum growth factor(s) requirement. These results provide a framework for future experiments to further elucidate the function of CCRG.

The Cancer Genome Anatomy Project (CGAP) database of the National Cancer Institute contains thousands of expressed sequences, both known and novel, derived from diverse sets of normal, precancerous, and tumor cDNA libraries. This offers the possibility of using this database as a rational starting point for bioinformatics-based cancer gene discovery. Using the Digital Differential Display tool of the CGAP database, a hypothesis-driven gene discovery approach was undertaken to analyze differential expression of various solid tumor types. Two hundred known genes and five hundred novel sequences were discovered to be differentially expressed, and a comprehensive database was established to facilitate identification of cancer diagnostic and therapeutic targets. To validate the use of bioinformatics in discovering genes with organ- and tumor-selectivity, novel ESTs predicted to be colon tumor-specific were analyzed further for expression specificity. Reverse Transcriptase-Polymerase Chain Reaction (RT-PCR) analysis using matched sets of colon normal- and tumor-derived cDNAs identified one EST to be specifically expressed in the majority of colon tumors and normal small intestine. Due to this apparent specificity, the gene was termed Colon Carcinoma Related Gene (CCRG). Based on protein sequence analysis, CCRG belongs to a novel class of secreted factors. Another gene identified in this study showed homology to Single Minded 2 gene (SIM2). Involvement between SIM2 and cancer has not yet been reported. Isoform-specific expression of SIM2 short-form (SIM2-s) was seen in colon, pancreas, and prostate carcinomas but not in most normal tissues. Using a large collection of paraffin sections from colon, pancreas, and prostate tumor and normal tissues, elevated protein expression was seen in tumors compared to normal tissue specimens, demonstrating the diagnostic potential of SIM2-s. Antisense inhibition of SIM2-s expression in colon and pancreatic cancer cell lines caused inhibition of gene expression, growth inhibition, and apoptosis. Administration of SIM2-s antisense in nude mice caused inhibition of colon tumor growth without pronounced gross toxicity. Using GeneChipRTM technology, a gene expression profile indicative of apoptosis was observed in the colon cancer model. CCRG and SIM2-s offer both a diagnostic and therapeutic potential in select cancers and validate the use of bioinformatics approaches in the gene discovery paradigm.

Experimentally naive rats show variance in their locomotor reactivity to novelty, some displaying higher (HR) while others displaying lower (LR) reactivity, associated with vulnerability to stress. LRHR phenotype is proposed as an antecedent to the development of stress hyper responsiveness. Results presented here show emergence of antidepressive-like behavior following peripubertal-juvenile exposure to chronic variable physical (CVP) and chronic variable social stress (CVS) in HR rats, and depressive-like behavior following CVP in the LRs. The antidepressive-like behavior in HR rats was accompanied by increased levels of acetylated Histone3 (acH3) and acetylated Histone4 (acH4) at the hippocampal brain-derived neurotrophic factor (BDNF) P2 and P4 promoters respectively. This effect may mediate increased mossy fibre (MF) terminal field size, particularly the suprapyramidal mossy fibre projection volume (SP-MF), in the HR animals following both stress regimens. These findings show that chronic variable stress during adolescence induces individual differences in molecular, neuromorphological and behavioral parameters between LRs and HRs, which provides further evidence that individual differences in stress responsiveness is an important factor in resistance or vulnerability to stress-induced depression and/or anxiety.

Sponges are an important source of bioactive marine natural products, or secondary metabolites. The common Caribbean reef sponge, Axinella corrugata, produces an antitumor and antibacterial chemical, stevensine. This study determined whether environmental stressors, such as elevated temperature and exposure to Amphibalanus amphitrite larvae, affect the production of stevensine by A.corrugata and if the stressors caused A.corrugata to exhibit differential gene expression. Temperature stress resulted in no significant change in the production of stevensine; only two genes were significantly differentially expressed, including hsp70. Larval stressed resulted in increased production of stevensine and significant differential gene expression (more than seventy genes). This study suggests that A.corrugata may be resilient to elevations in temperature and that one of stevensine's roles in nature is as an antifoulant.

The zinc finger associated domain (ZAD) family of transcription factors from Drosophila melanogaster is not well described in the literature, in part because it is very difficult to study by traditional mutagenesis screens. Bioinformatic studies indicate this is due to overlapping functions remaining after a recent evolutionary divergence. I set out to use in vitro-binding techniques to identify the characteristics of the ZAD family and test this theory. I have constructed glutathione S-transferase (GST)-ZAD domain chimeric proteins for use in pull down protein binding assays,and GST-Zinc finger (ZnF) array domain chimera for electrophoretic mobility shift assays (EMSA). Protein binding assays indicated two putative conserved interactors, similar to the analogous KRAB system in mammals. ... Competitive bindings were carried out to show a specificity of binding conferred by the identified conserved positions. While the consensus binding sites show relatively few similarities, the predicted target genes identified by the consensus binding sites show significant overlap. The nature of this overlap conforms to the known characteristics of the ZAD family but points to a more positive selection to maintain conservation of function.

The assembly and maintenance of central synapses is a complex process, requiring myriad genes and their products. Highwire is a large gene containing a RING domain, characteristic of ubiquitin E3 ligases. Highwire has been shown to restrain axon growth and control synaptogenesis at a peripheral synapse. Here I examine the roles of Highwire at a central synapse in the adult Drosophila Giant Fiber System (GFS). Highwire is indeed necessary for proper axonal growth as well as synaptic transmission in the GFS. Differences arise between the central synapse and the neuromuscular junction (NMJ), where highwire was initially characterized : expresion from the postsynaptic cell can rescue highwire synaptic defects, which is not seen at the NMJ. In addition, a MAP kinase signaling pathway regulated by highwire at the NMJ has differing roles at a central synapse. Wallenda MAPK can rescue not only the highwire anatomical phenotype but also the defects seen in transmission. Another distinction is seen here : loss of function basket and Dfos enhance the highwire anatomical phenotype while expression of dominant negative basket and Dfos suppress the highwire phenotype. As a result we have compared the signaling pathway in flies and worms and found that the NMJ in the two organisms use a parallel pathway while the central synapse uses a distinct pathway.

MicroRNAs (miRNAs) may serve as diagnostic and predictive biomarkers for cancer. The aim of this study was to identify novel cancer biomarkers from miRNA datasets, in addition to those already known. Three published miRNA cancer datasets (liver, breast, and brain) were evaluated, and the performance of the entire feature set was compared to the performance of individual feature filters, an ensemble of those filters, and a support vector machine (SVM) wrapper. In addition to confirming many known biomarkers, the main contribution of this study is that seven miRNAs have been newly identified by our ensemble methodology as possible important biomarkers for hepatocellular carcinoma or breast cancer, pending wet lab confirmation. These biomarkers were identified from miRNA expression datasets by combining multiple feature selection techniques (i.e., creating an ensemble) or by the SVM-wrapper, and then classified by different learners. Generally speaking, creating a subset of features by selecting only the highest ranking features (miRNAs) improved upon results generated when using all the miRNAs, and the ensemble and SVM-wrapper approaches outperformed individual feature selection methods. Finally, an algorithm to determine the number of top-ranked features to include in the creation of feature subsets was developed. This algorithm takes into account the performance improvement gained by adding additional features compared to the cost of adding those features.