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Transcriptome profiling and the pathogenesis of diabetic complications.

Diabetes is an escalating problem worldwide and a major cause of vascular disease, renal failure, and blindness, among other complications. The cellular mediators of high glucose-induced injury include activation of protein kinase C, accumulation of cell sorbitol from increased flux through the aldose reductase pathway, and generation of advanced glycosylation end products and reactive oxygen species, among others. Current strategies for preventing and slowing the progression of the macrovascular and microvascular complications of diabetes include optimization of glycemic control and BP, angiotensin-converting enzyme inhibitors and angiotensin II blockers, and HMG CoA reductase inhibitors. However, there is an urgent need to develop new therapeutic strategies, as these interventions, although they may slow, rarely halt the progression of diabetic complications. Central to this process is the elucidation of the molecular events that drive this complex disease and that are potential therapeutic targets. This review discusses the promise offered in this regard by global monitoring of cellular or tissue mRNA expression (so-called transcriptomics) and illustrates the potential of this approach by focusing on recent studies on the pathogenesis of diabetic nephropathy.

Actins↗

Transcriptome profiling of a Saccharomyces cerevisiae mutant with a constitutively activated Ras/cAMP pathway.

Often changes in gene expression levels have been considered significant only when above/below some arbitrarily chosen threshold. We investigated the effect of applying a purely statistical approach to microarray analysis and demonstrated that small changes in gene expression have biological significance. Whole genome microarray analysis of a pde2Delta mutant, constructed in the Saccharomyces cerevisiae reference strain FY23, revealed altered expression of approximately 11% of protein encoding genes. The mutant, characterized by constitutive activation of the Ras/cAMP pathway, has increased sensitivity to stress, reduced ability to assimilate nonfermentable carbon sources, and some cell wall integrity defects. Applying the Munich Information Centre for Protein Sequences (MIPS) functional categories revealed increased expression of genes related to ribosome biogenesis and downregulation of genes in the cell rescue, defense, cell death and aging category, suggesting a decreased response to stress conditions. A reduced level of gene expression in the unfolded protein response pathway (UPR) was observed. Cell wall genes whose expression was affected by this mutation were also identified. Several of the cAMP-responsive orphan genes, upon further investigation, revealed cell wall functions; others had previously unidentified phenotypes assigned to them. This investigation provides a statistical global transcriptome analysis of the cellular response to constitutive activation of the Ras/cAMP pathway.

Cell Wall↗

Comparative proteome analysis of Staphylococcus aureus biofilm and planktonic cells and correlation with transcriptome profiling.

Pathogenic staphylococci can form biofilms in which they show a higher resistance to antibiotics and the immune defense system than their planktonic counterparts, which suggests that the cells in a biofilm have an altered metabolic activity. Here, 2-D PAGE was used to identify secreted, cell wall-associated and cytoplasmic proteins expressed in Staphylococcus aureus after 8 and 48 h of growth. The proteins were separated at pH ranges of 4-7 or 6-11. The protein patterns revealed significant differences in 427 protein spots; from these, 258 non-redundant proteins were identified using ESI-MS/MS. Biofilm cells expressed higher levels of proteins associated with cell attachment and peptidoglycan synthesis, and in particular fibrinogen-binding proteins. Enzymes involved in pyruvate and formate metabolism were upregulated. Furthermore, biofilm cells expressed more staphylococcal accessory regulator A protein (SarA), which corroborates the positive effect of SarA on the expression of the intercellular adhesion operon ica and biofilm growth. In contrast, proteins, such as proteases and particularly immunodominant antigen A (IsaA) and staphylococcal secretory antigen (SsaA), were found in lower amounts. The RNA expression profiling largely supports the proteomic data. The results were mapped onto KEGG pathways.

Bacterial Proteins↗

Transcriptome profiling of lung schistosomula,in vitro cultured schistosomula and adult Schistosoma japonicum.

The schistosomulum is the main target of vaccine-induced protective immunity; however, most studies have utilized schistosomula produced by mechanical transformation of infective larvae followed by in vitro culture rather than larvae isolated directly from the lungs of infected mammals. Using transmission electron microscopy, we demonstrated that there was little difference in the ultrastructure of Schistosoma japonicum schistosomula obtained by the two methods. However, significant differences in gene expression profiles were apparent when we used an oligonucleotide microarray to compare the gene expression profiles of schistosomula obtained in vivo from lung tissue with those maintained in vitro, and with adult worms of S. japonicum. It is likely that host environmental factors, which cannot be reliably reproduced in vitro, do influence the growth, development and overall biology of schistosomes. Thus caution is urged when using in vitro-cultured schistosomes and mechanically transformed/cultured schistosomula in molecular, biochemical and immunological studies.

Animals↗

Distinct developmental defense activations in barley embryos identified by transcriptome profiling.

Proper embryo development is crucial for normal growth and development of barley. Numerous related aspects of this process--for example how the embryo establishes and sustains disease resistance for extended periods during dormancy--remain largely unknown. Here we report the results of microarray analyses of >22,000 genes, which together with measurements of jasmonic acid and salicylic acid during embryo development provide new information on the initiation in the developing barley embryo of at least two distinct types of developmental defense activation (DDA). Early DDA is characterized by the up-regulation of a specific set of genes around 20 days after flowering, including co-regulation of those for encoding 9-lipoxygenase and several oxylipin-generating enzymes, possibly leading to the formation of alpha-ketols. The same developmental phase includes an up-regulation of several defense genes, and indications of co-regulation of those for enzymes involved in the generation of phenylpropanoid phytoalexins. Late DDA is initiated prior to grain desiccation, around 37 days after flowering, with up-regulation of several genes encoding proteins with roles in antioxidant responses as well as a simultaneous up-regulation of several PR genes is notable. Throughout barley embryo development, there are no indications of an increased biosynthesis of either jasmonic acid or salicylic acid. Collectively, the results help explain how the proposed DDA enables protection of the developing barley embryo and grain for purposes of disease resistance.

Cell Cycle↗

Identification of changes in the transcriptome profile of human hepatoma HepG2 cells stimulated with interleukin-1 beta.

Interleukin-1 (IL-1) is the principal pro-inflammatory cytokine participating in the initiation of acute phase response. Human hepatoma HepG2 cells were exposed to 15 ng/ml of IL-1beta for times ranging from 1 to 24 h and the total RNA was isolated. Then cDNA was obtained and used for differential display with 10 arbitrary primers and 9 oligo(dT) primers designed by Clontech. Validation of observed changes of differentially expressed known genes was carried out by RT-PCR or Northern blot analysis. Out of 90 cDNA strands modulated by IL-1, 46 have been successfully reamplified and their sequencing indicates that they represent 36 different cDNA templates. By GenBank search, 26 cDNA clones were identified as already known genes while 10 showed no homology to any known gene. The identified transcripts modulated by IL-1 in HepG2 cells code for intracellular proteins of various function: trafficking/motor proteins (3 genes), proteins participating in the translation machinery or posttranscriptional/posttranslational modifications (7 genes), proteases (1 gene), proteins involved in metabolism (6 genes), activity modulators (3 genes), proteins of the cell cycle machinery (2 genes) and those functionally unclassified (4 genes). Majority of genes responded to IL-1 within 1 to 6 h (early genes), while two were late response genes (12-24 h) and four showed prolonged response over the whole 24-h period. Most of the observed changes of expression were in the range of two- to threefold increase in comparison to control untreated cells. Among identified genes, no typical secretory acute phase protein was found. The obtained results suggest that IL-1 affects the expression of several genes in HepG2 cells, especially those engaged in the synthesis and modifications of proteins.

Carcinoma, Hepatocellular↗

Genome-wide transcriptome profiling of the early cadmium response of Arabidopsis roots and shoots.

Transcriptional regulation in response to cadmium treatment was investigated in both roots and leaves of Arabidopsis, using the whole genome CATMA microarray containing at least 24,576 independent probe sets. Arabidopsis plants were hydroponically treated with low (5 microM) or high (50 microM) cadmium concentrations during 2, 6, and 30 hours. At each time point, Cd level was determined using ICP-AES showing that both plant tissues are able to accumulate the heavy metal. RT-PCR of eight randomly selected genes confirmed the reliability of our microarray results. Analyses of response profiles demonstrate the existence of a regulatory network that differentially modulates gene expression in a tissue- and kinetic-specific manner in response to cadmium. One of the main response observed in roots was the induction of genes involved in sulfur assimilation-reduction and glutathione (GSH) metabolism. In addition, HPLC analysis of GSH and phytochelatin (PC) content shows a transient decrease of GSH after 2 and 6 h of metal treatment in roots correlated with an increase of PC contents. Altogether, our results suggest that to cope with cadmium, plants activate the sulfur assimilation pathway by increasing transcription of related genes to provide an enhanced supply of GSH for PC biosynthesis. Interestingly, in leaves an early induction of several genes encoding enzymes involved in the biosynthesis of phenylpropanoids was observed. Finally, our results provide new insights to understand the molecular mechanisms involved in transcriptional regulation in response to cadmium exposure in plants.

Arabidopsis↗

Global survey of organ and organelle protein expression in mouse: combined proteomic and transcriptomic profiling.

Organs and organelles represent core biological systems in mammals, but the diversity in protein composition remains unclear. Here, we combine subcellular fractionation with exhaustive tandem mass spectrometry-based shotgun sequencing to examine the protein content of four major organellar compartments (cytosol, membranes [microsomes], mitochondria, and nuclei) in six organs (brain, heart, kidney, liver, lung, and placenta) of the laboratory mouse, Mus musculus. Using rigorous statistical filtering and machine-learning methods, the subcellular localization of 3274 of the 4768 proteins identified was determined with high confidence, including 1503 previously uncharacterized factors, while tissue selectivity was evaluated by comparison to previously reported mRNA expression patterns. This molecular compendium, fully accessible via a searchable web-browser interface, serves as a reliable reference of the expressed tissue and organelle proteomes of a leading model mammal.

Animals↗

Transcriptome profile within the mouse central nervous system and activation of myelin-reactive T cells following murine coronavirus infection.

Multiple sclerosis (MS) is an autoimmune disease associated with environmental factors, possibly including several viruses such as the coronaviruses. Indeed, murine coronavirus (MHV) infection provides a well-known experimental model for MS studies. Intracerebral infection of C57BL/6 mice with MHV-A59 revealed that viral replication was efficient and that clearance of infectious virus occurred as soon as 7 days post-infection. Using cDNA arrays, analysis of gene expression profile in the brain revealed a modulation of 80 different genes following infection, with at least 27 of these genes having previously been directly related to innate or acquired immune responses. Concordingly, an important activation of auto-reactive T cells specific to myelin basic protein was demonstrated. Altogether, these results indicate that an MHV infection of the central nervous system (CNS) leads to an important host genomic response implicating immunity-related genes and to the activation of myelin-reactive autoimmune T cells.

Animals↗

Transcriptome profiling reveals similarities and differences in plant responses to cadmium and lead.

We analyzed the influence of salts of two heavy metals--lead and cadmium (Pb2+ and Cd2+) on plants, including plant and root size, plant genome stability as well as global genome expression. Measurement of the metal uptake showed that there was a significantly higher incorporation of Cd than of Pb, 0.6 and 0.15 uM per gram of dry weight, respectively. The analysis of the root length and plant size showed a dose dependent decrease in plants exposed to cadmium. In contrast there was little difference in the size of plants exposed to lead, although there was nearly four-fold increase of the root length. Analysis of the genome stability revealed that cadmium led to a dose dependent increase of homologous recombination whereas lead had no effect. Analysis of the global genome expression of plants chronically exposed to 50 uM of Cd and Pb revealed 65 and 338 up- and down-regulated genes by Cd and 19 and 76 by Pb, respectively. Interestingly, half of the genes that changed their expression in Pb-treated plants also changed their expression in Cd-treated ones. The greater number of genes regulated by Cd reflects generally higher genome instability of plants as well as higher uptake as compared to Pb.

Arabidopsis↗

Differential transcriptome profiling identifies Plasmodium genes encoding pre-erythrocytic stage-specific proteins.

Invasive sporozoite and merozoite stages of malaria parasites that infect mammals enter and subsequently reside in hepatocytes and red blood cells respectively. Each invasive stage may exhibit unique adaptations that allow it to interact with and survive in its distinct host cell environment, and these adaptations are likely to be controlled by differential gene expression. We used suppression subtractive hybridization (SSH) of Plasmodium yoelii salivary gland sporozoites versus merozoites to identify stage-specific pre-erythrocytic transcripts. Sequencing of the SSH library and matching the cDNA sequences to the P. yoelii genome yielded 25 redundantly tagged genes including the only two previously characterized sporozoite-specific genes encoding the circumsporozoite protein (CSP) and thrombospondin-related anonymous protein (TRAP). Twelve novel genes encode predicted proteins with signal peptides, indicating that they enter the secretory pathway of the sporozoite. We show that one novel protein bearing a thrombospondin type 1 repeat (TSR) exhibits an expression pattern that suggests localization in the sporozoite secretory rhoptry organelles. In addition, we identified a group of four genes encoding putative low-molecular-mass proteins. Two proteins in this group exhibit an expression pattern similar to TRAP, and thus possibly localize in the sporozoite secretory micronemes. Proteins encoded by the differentially expressed genes identified here probably mediate specific interactions of the sporozoite with the mosquito vector salivary glands or the mammalian host hepatocyte and are not used during merozoite-red blood cell interactions.

Amino Acid Sequence↗

Transcriptome profiling to identify genes involved in peroxisome assembly and function.

Yeast cells were induced to proliferate peroxisomes, and microarray transcriptional profiling was used to identify PEX genes encoding peroxins involved in peroxisome assembly and genes involved in peroxisome function. Clustering algorithms identified 224 genes with expression profiles similar to those of genes encoding peroxisomal proteins and genes involved in peroxisome biogenesis. Several previously uncharacterized genes were identified, two of which, YPL112c and YOR084w, encode proteins of the peroxisomal membrane and matrix, respectively. Ypl112p, renamed Pex25p, is a novel peroxin required for the regulation of peroxisome size and maintenance. These studies demonstrate the utility of comparative gene profiling as an alternative to functional assays to identify genes with roles in peroxisome biogenesis.

Gene Expression Profiling↗

Within-tree transcriptome profiling in wood-forming tissues of a fast-growing Eucalyptus tree.

Despite the availability of high-throughput transcript profiling technology, little is known about tissue-specific gene expression patterns in the wood-forming tissues of Eucalyptus plantation tree species. We used cDNA-amplified fragment length polymorphism (AFLP) analysis in combination with infrared fragment detection and semi-automated band quantification to profile gene expression in a 6-year-old, fast- growing Eucalyptus tree. The expression profiles of 6385 transcript-derived fragments (TDFs) were analyzed across four major woody tissues (mature xylem, immature xylem, phloem and cork) collected from two stem positions, to provide a global view of transcript abundance and variability in the Eucalyptus stem. About 21% of the TDFs were differentially expressed and could be grouped into clusters representing co- expressed genes. A total of 71 TDFs representing different gene clusters were isolated and characterized. These included genes implicated in cell fate, signal transduction and cell wall biosynthesis, processes closely associated with xylogenesis. Analysis of the expression levels of selected TDFs by quantitative RT-PCR corroborated the TDF quantification and confirmed that cDNA-AFLP analysis is a highly efficient and accurate tool for transcript profiling and gene discovery in wood-forming tissues of tree species.

Cluster Analysis↗

Combined transcriptome profiling reveals a novel family of arbuscular mycorrhizal-specific Medicago truncatula lectin genes.

The large majority of plants are capable of undergoing a tight symbiosis with arbuscular mycorrhizal (AM) fungi. During this symbiosis, highly specialized new structures called arbuscules are formed within the host cells, indicating that, during interaction with AM fungi, plants express AM-specific genetic programs. Despite increasing efforts, the number of genes known to be induced in the AM symbiosis is still low. In order to identify novel AM-induced genes which have not been listed before, 5,646 expressed sequence tags (ESTs) were generated from two Medicago truncatula cDNA libraries: a random cDNA library (MtAmp) and a suppression subtractive hybridization (SSH) library (MtGim), the latter being designed to enhance the cloning of mycorrhiza-upregulated genes. In silico expression analysis was applied to identify those tentative consensus sequences (TCs) of The Institute for Genomic Research M. truncatula gene index (MtGI) that are composed exclusively of ESTs deriving from the MtGim or MtAmp library, but not from any other cDNA library of the MtGI. This search revealed 115 MtAmp- or MTGim-specific TCs. For the majority of these TCs with sequence similarities to plant genes, the AM-specific expression was verified by quantitative reverse-transcription polymerase chain reaction. Annotation of the novel genes induced in mycorrhizal roots suggested their involvement in different transport as well as signaling processes and revealed a novel family of AM-specific lectin genes. The expression of reporter gene fusions in transgenic roots revealed an arbuscule-related expression of two members of the lectin gene family, indicating a role for AM-specific lectins during arbuscule formation or functioning.

Amino Acid Sequence↗

Transcriptome profiling of the response of Arabidopsis suspension culture cells to Suc starvation.

Upon encountering nutrient stress conditions, plant cells undergo extensive metabolic changes and induce nutrient recycling pathways for their continued survival. The role of nutrient mobilization in the response of Arabidopsis suspension cells to Suc starvation was examined. Vacuolar autophagy was induced within 24 h of starvation, with increased expression of vacuolar proteases that are likely to be required for degradation of cytoplasmic components delivered to the vacuole, and thus for nutrient recycling. After 48 h of starvation, culture viability began to decrease, and substantial cell death was evident by 72 h. To provide further insight into the pathways required for survival during Suc deficit, transcriptional profiling during Suc starvation was performed using the ATH1 GeneChip array containing 22,810 probe sets. A significant increase in transcript levels was observed for 343 genes within 48 h of starvation, indicating a response to nutrient stress that utilizes the recycling of cellular components and nutrient scavenging for maintaining cell function, the protection of the cell from death through activation of various defense and stress response pathways, and regulation of these processes by specific protein kinases and transcription factors. These physiological and molecular data support a model in which plant cells initiate a coordinated response of nutrient mobilization at the onset of Suc depletion that is able to maintain cell viability for up to 48 h. After this point, genes potentially involved in cell death increase in expression, whereas those functioning in translation and replication decrease, leading to a decrease in culture viability and activation of cell death programs.

Arabidopsis↗

Transcriptome profiling, molecular biological, and physiological studies reveal a major role for ethylene in cotton fiber cell elongation.

Upland cotton (Gossypium hirsutum) produces the most widely used natural fibers, yet the regulatory mechanisms governing fiber cell elongation are not well understood. Through sequencing of a cotton fiber cDNA library and subsequent microarray analysis, we found that ethylene biosynthesis is one of the most significantly upregulated biochemical pathways during fiber elongation. The 1-Aminocyclopropane-1-Carboxylic Acid Oxidase1-3 (ACO1-3) genes responsible for ethylene production were expressed at significantly higher levels during this growth stage. The amount of ethylene released from cultured ovules correlated with ACO expression and the rate of fiber growth. Exogenously applied ethylene promoted robust fiber cell expansion, whereas its biosynthetic inhibitor l-(2-aminoethoxyvinyl)-glycine (AVG) specifically suppressed fiber growth. The brassinosteroid (BR) biosynthetic pathway was modestly upregulated during this growth stage, and treatment with BR or its biosynthetic inhibitor brassinazole (BRZ) also promoted or inhibited, respectively, fiber growth. However, the effect of ethylene treatment was much stronger than that of BR, and the inhibitory effect of BRZ on fiber cells could be overcome by ethylene, but the AVG effect was much less reversed by BR. These results indicate that ethylene plays a major role in promoting cotton fiber elongation. Furthermore, ethylene may promote cell elongation by increasing the expression of sucrose synthase, tubulin, and expansin genes.

Amino Acids, Cyclic↗

Arcuate nucleus transcriptome profiling identifies ankyrin repeat and suppressor of cytokine signalling box-containing protein 4 as a gene regulated by fasting in central nervous system feeding circuits.

The arcuate nucleus of the hypothalamus is a primary site for sensing blood borne nutrients and hormonal messengers that reflect caloric status. To identify novel energy homeostatic genes, we examined RNA extracts from the microdissected arcuate nucleus of fed and 48-h fasted rats using oligonucleotide microarrays. The relative abundance of 118 mRNA transcripts was increased and 203 mRNA transcripts was decreased during fasting. One of the down-regulated mRNAs was ankyrin-repeat and suppressor of cytokine signalling box-containing protein 4 (Asb-4). The predicted structure of Asb-4 protein suggested that it might encode an intracellular regulatory protein, and therefore its mRNA expression was investigated further. Reverse transcription quantitative polymerase chain reaction was used to validate down-regulation of Asb-4 mRNA in the arcuate nucleus of the fasted Sprague-Dawley rat (relative expression of Asb-4 mRNA: fed = 4.66 +/- 0.26; fasted = 3.96 +/- 0.23; n = 4, P < 0.01). Down-regulation was also demonstrated in the obese fa/fa Zucker rat, another model of energy disequilibrium (relative expression of Asb-4 mRNA: lean Zucker = 3.91 +/- 0.32; fa/fa = 2.93 +/- 0.26; n = 5, P < 0.001). In situ hybridisation shows that Asb-4 mRNA is expressed in brain areas linked to energy homeostasis, including the arcuate nucleus, paraventricular nucleus, dorsomedial nucleus, lateral hypothalamus and posterodorsal medial amygdaloid area. Double in situ hybridisation revealed that Asb-4 mRNA colocalises with key energy homeostatic neurones. In the fed state, Asb-4 mRNA is expressed by 95.6% of pro-opiomelanocortin (POMC) neurones and 46.4% of neuropeptide Y (NPY) neurones. By contrast, in the fasted state, the percentage of POMC neurones expressing Asb-4 mRNA drops to 73.2% (P < 0.001). Moreover, the density of Asb-4 mRNA per fasted POMC neurone is markedly decreased. Conversely, expression of Asb-4 mRNA by NPY neurones in the fasted state is modestly increased to 52.7% (P < 0.05). Based on its differential expression, neuroanatomical distribution and colocalisation, we hypothesise that Asb-4 is a gene involved in energy homeostasis.

Animals↗

Long serial analysis of gene expression for gene discovery and transcriptome profiling in the widespread marine coccolithophore Emiliania huxleyi.

The abundant and widespread coccolithophore Emiliania huxleyi plays an important role in mediating CO2 exchange between the ocean and the atmosphere through its impact on marine photosynthesis and calcification. Here, we use long serial analysis of gene expression (SAGE) to identify E. huxleyi genes responsive to nitrogen (N) or phosphorus (P) starvation. Long SAGE is an elegant approach for examining quantitative and comprehensive gene expression patterns without a priori knowledge of gene sequences via the detection of 21-bp nucleotide sequence tags. E. huxleyi appears to have a robust transcriptional-level response to macronutrient deficiency, with 42 tags uniquely present or up-regulated twofold or greater in the N-starved library and 128 tags uniquely present or up-regulated twofold or greater in the P-starved library. The expression patterns of several tags were validated with reverse transcriptase PCR. Roughly 48% of these differentially expressed tags could be mapped to publicly available genomic or expressed sequence tag (EST) sequence data. For example, in the P-starved library a number of the tags mapped to genes with a role in P scavenging, including a putative phosphate-repressible permease and a putative polyphosphate synthetase. In short, the long SAGE analyses have (i) identified many new differentially regulated gene sequences, (ii) assigned regulation data to EST sequences with no database homology and unknown function, and (iii) highlighted previously uncharacterized aspects of E. huxleyi N and P physiology. To this end, our long SAGE libraries provide a new public resource for gene discovery and transcriptional analysis in this biogeochemically important marine organism.

Base Sequence↗