Comparative gene expression profiling by oligonucleotide fingerprinting.

The use of hybridisation of synthetic oligonucleotides to cDNAs under high stringency to characterise gene sequences has been demonstrated by a number of groups. We have used two cDNA libraries of 9 and 12 day mouse embryos (24 133 and 34 783 clones respectively) in a pilot study to characterise expressed genes by hybridisation with 110 hybridisation probes. We have identified 33 369 clusters of cDNA clones, that ranged in representation from 1 to 487 copies (0.7%). 737 were assigned to known rodent genes, and a further 13 845 showed significant homologies. A total of 404 clusters were identified as significantly differentially represented (P < 0.01) between the two cDNA libraries. This study demonstrates the utility of the fingerprinting approach for the generation of comparative gene expression profiles through the analysis of cDNAs derived from different biological materials.     

Heterologous array analysis in Pinaceae: hybridization of Pinus taeda cDNA arrays with cDNA from needles and embryogenic cultures of P. Taeda, P. Sylvestris or Picea abies

Hybridization of labelled cDNA from various cell types with high-density arrays of expressed sequence tags is a powerful technique for investigating gene expression. Few conifer cDNA libraries have been sequenced. Because of the high level of sequence conservation between Pinus and Picea we have investigated the use of arrays from one genus for studies of gene expression in the other. The partial cDNAs from 384 identifiable genes expressed in differentiating xylem of Pinus taeda were printed on nylon membranes in randomized replicates. These were hybridized with labelled cDNA from needles or embryogenic cultures of Pinus taeda, P. sylvestris and Picea abies, and with labelled cDNA from leaves of Nicotiana tabacum. The Spearman correlation of gene expression for pairs of conifer species was high for needles (r(2) = 0.78 - 0.86), and somewhat lower for embryogenic cultures (r(2) = 0.68 - 0.83). The correlation of gene expression for tobacco leaves and needles of each of the three conifer species was lower but sufficiently high (r(2) = 0.52 - 0.63) to suggest that many partial gene sequences are conserved in angiosperms and gymnosperms. Heterologous probing was further used to identify tissue-specific gene expression over species boundaries. To evaluate the significance of differences in gene expression, conventional parametric tests were compared with permutation tests after four methods of normalization. Permutation tests after Z-normalization provide the highest degree of discrimination but may enhance the probability of type I errors. It is concluded that arrays of cDNA from loblolly pine are useful for studies of gene expression in other pines or spruces.     

DNA sequence-based "bar codes" for tracking the origins of expressed sequence tags from a maize cDNA library constructed using multiple mRNA sources

To enhance gene discovery, expressed sequence tag (EST) projects often make use of cDNA libraries produced using diverse mixtures of mRNAs. As such, expression data are lost because the origins of the resulting ESTs cannot be determined. Alternatively, multiple libraries can be prepared, each from a more restricted source of mRNAs. Although this approach allows the origins of ESTs to be determined, it requires the production of multiple libraries. A hybrid approach is reported here. A cDNA library was prepared using 21 different pools of maize (Zea mays) mRNAs. DNA sequence "bar codes" were added during first-strand cDNA synthesis to uniquely identify the mRNA source pool from which individual cDNAs were derived. Using a decoding algorithm that included error correction, it was possible to identify the source mRNA pool of more than 97% of the ESTs. The frequency at which a bar code is represented in an EST contig should be proportional to the abundance of the corresponding mRNA in the source pool. Consistent with this, all ESTs derived from several genes (zein and adh1) that are known to be exclusively expressed in kernels or preferentially expressed under anaerobic conditions, respectively, were exclusively tagged with bar codes associated with mRNA pools prepared from kernel and anaerobically treated seedlings, respectively. Hence, by allowing for the retention of expression data, the bar coding of cDNA libraries can enhance the value of EST projects.     

PCR-based immortalization and screening of hierarchical pools of cDNAs.

Starting from sequences of at least 60 bp, PCR-based screening has been developed to recover cDNAs from libraries without the necessity for hybridization or extensive DNA extraction steps. The method maintains the indefinite availability of even scarce cDNA libraries and provides an estimate of the relative abundance of the mRNA species. Isolation of a cDNA clone can be done in less than a week. cDNAs were isolated that were cognate for fragments of expressed sequences and for an exon predicted from genomic sequence.     

The NOLA2 and RPS3A genes as highly informative markers for human squamous cell lung cancer

cDNA libraries enriched with sequences that are differentially transcribed in normal and tumor tissues were prepared using the subtractive hybridization of mixtures of cDNAs from ten patients with squamous cell lung cancer and the corresponding mixtures of cDNAs from normal tissues of the same patients. An analysis of the libraries revealed two genes, NOLA2 and RPS3A, whose expression in patients with squamous cell lung cancer increased by 70%. A high frequency of enhanced expression of these genes in the cancer makes them highly informative markers of squamous cell lung cancer, which, together with other markers, can be used for reliable diagnosis of the disease.     

Screening of Rice Genes from the cDNA Catalog Using the Data Obtained by Protein Sequencing

The partial amino acid sequences of 121 rice proteins separated by two-dimensional gel electrophoresis (2D-PAGE), were determined for a protein sequence data file. In the Rice Genome Research Program (RGP), more than 20,000 cDNA clones randomly selected from rice cDNA libraries have been sequenced to construct a cDNA catalog. Complimentary DNAs encoding about 30% of proteins in the protein sequence data file could be identified in the catalog by computer search. It was deduced that 20,000–40,000 genes are present in the rice genome. Only half of about 20,000 cDNAs sequenced in the RGP, corresponding to 1/4–1/2 of genes present in the entire rice genome, should have unique sequences after considering gene redundancy. This is consistent with the fact that the cDNAs encoding about 30% of the sequenced proteins could be identified in the catalog. If the size of the cDNA catalog is enlarged further, cDNAs encoding all proteins separated by 2D-PAGE could be easily identified from the catalog by using the protein sequence data.     

Global amplification of cDNA from limiting amounts of tissue. An improved method for gene cloning and analysis

In this study we present an improved polymerase chain reaction (PCR)-based methodology to generate large amounts of high-quality complementary DNA (cDNA) from small amounts of initial total RNA. Global amplification of cDNA makes it possible to simultaneously clone many cDNAs and to construct directional cDNA libraries from a sequence-abundance-normalized cDNA population, and also permits rapid amplification of cDNA ends (RACE), from a limited amount of starting material. The priming of cDNAs with an adapter oligo-deoxythymidine (oligo-dT) primer and the ligation of a modified oligonucleotide to the 3′ end of single-stranded cDNAs, through the use of T4 RNA ligase, generates known sequences on either end of the cDNA population. This helps in the global amplification of cDNAs and in the sequence-abundance normalization of the cDNA population through the use of PCR. Utilization of a long-range PCR enzyme mix to amplify the cDNA population helps to reduce bias toward the preferential amplification of shorter molecules. Incorporation of restriction sites in the PCR primers allows the amplified cDNAs to be directionally cloned into appropriate cloning vectors to generate cDNA libraries. RACE-PCR done with biotinylated primers and streptavidin-coated para-magnetic particles are used for the efficient isolation of either full-length coding or noncoding strands.     

Identification of grapevine aquaporins and expression analysis in developing berries

Aquaporins are membrane water channels that play critical roles in controlling the water content of cells and tissues. In this work, nine full-length cDNAs encoding putative aquaporins were isolated from grape berry cDNA libraries. A phylogenetic analysis conducted with 28 aquaporin genes identified in the grapevine genome and previously characterized aquaporins from Arabidopsis indicates that three cDNAs encode putative tonoplast aquaporins (TIPs) whereas six cDNAs belong to the plasma membrane aquaporin subfamily (PIPs). Specific probes designed on the 3' untranslated regions of each cDNA were used for the preparation of cDNA macroarray filters and in situ hybridization experiments. Macroarray data indicate that expression levels of most TIP and PIP genes depend on grape berry developmental stages and point out to a global decrease of aquaporin gene expression during berry ripening. In young berries, high expression of aquaporin genes was preferentially observed in dividing and elongating cells and in cells involved in water and solutes transport. Taken together, the data provided in this paper indicate that aquaporins are implicated in various physiological aspects of grape berry development.     

Prediction of the coding sequences of mouse homologues of KIAA gene: I. The complete nucleotide sequences of 100 mouse KIAA-homologous cDNAs identified by screening of terminal sequences of cDNA clones randomly sampled from size-fractionated libraries.

We have been conducting a human cDNA project to predict protein-coding sequences in long cDNAs (> 4 kb) since 1994. The number of these newly identified human genes exceeds 2000 and these genes are known as KIAA genes. As an extension of this project, we herein report characterization of cDNAs derived from mouse KIAA-homologous genes. A primary aim of this study was to prepare a set of mouse. KIAA-homologous cDNAs that could be used to analyze the physiological roles of KIAA genes in mice. In addition, comparison of the structures of mouse and human KIAA cDNAs might enable us to evaluate the integrity of KIAA cDNAs more convincingly. In this study, we selected mouse KIAA-homologous cDNA clones to be sequenced by screening a library of terminal sequences of mouse cDNAs in size-fractionated libraries. We present the entire sequences of 100 cDNA clones thus selected and predict their protein-coding sequences. The average size of the 100 cDNA sequences reached 5.1 kb and that of mouse KIAA-homologous proteins predicted from these cDNAs was 989 amino acid residues.     

Characterisation of red and white muscle myosin heavy chain gene coding sequences from antarctic and tropical fish

To understand molecular adaptation for locomotion at different environmental temperatures, we have studied the myosin heavy chain genes as these encode the molecular motors involved. For this purpose, cDNA libraries from white (fast) and red (slow) myotomal muscle of an Antarctic and a tropical fish were constructed and from these different myosin heavy chain cDNAs were isolated. Northern and in situ hybridisation confirmed in which type of muscle these isoform genes are expressed. The cDNAs were sequenced and the structure of the ATPase sites compared. There was a marked similarity between the tropical fast myosin and the Antarctic slow myosin in the loop 1 region, which has similar amino acid side chains, charge distribution and conformation. These findings help to explain why the myofibrils isolated from white muscle of tropical fish show a lower specific ATPase activity than the white muscle of Antarctic fish but a similar activity to the Antarctic red (slow) muscle. It also provides insight into the way molecular motors in Antarctic fish have evolved to produce more power and thus ensure effective swimming at near zero temperatures by the substitution or addition of a few residues in strategic regions, which include the ATPase site.     

Manganese superoxide dismutase: nucleotide and deduced amino acid sequence of a cDNA encoding a new human transcript.

Three human cDNA libraries were screened with a human manganese superoxide dismutase (Mn-SOD) cDNA under moderately stringent conditions to characterize a large 4-6 kb RNA species which hybridizes to Mn-SOD in RNA blot analyses. A new 4.2 kb Mn-SOD cDNA clone (Mn-SOD 1) was isolated. Its long 3426 nucleotide 3'-untranslated sequence contains both of the 240 base 3'-untranslated sequences of the 1 kb Mn-SOD 4 and 5 cDNAs. This is a fully processed, cytoplasmic RNA species and raises the possibility of a role for particular 3'-untranslated sequence selection in Mn-SOD gene regulation.     

ISOLATION AND CHARACTERIZATION OF PHASE-SPECIFIC COMPLEMENTARY DNAs FROM SPOROPHYTES AND GAMETOPHYTES OF PORPHYRA PURPUREA (RHODOPHYTA) USING SUBTRACTED COMPLEMENTARY DNA LIBRARIES1

The red alga Porphyra purpurea (Roth) C. Agardh has a life cycle that alternates between shell-boring, filamentous sporophytes and free-living, foliose gametophytes. The significant morphological differences between these two phases suggest that many genes should be developmentally regulated and expressed in a phase-specific manner. In this study, we prepared and screened subtracted complementary DNA (cDNA) libraries specific for the sporophyte and gametophyte of P. purpurea. This involved the construction of cDNA libraries from each phase, followed by the removal of common clones through subtractive hybridization. Sampling of the subtracted libraries indicated that 8–10% of the recombinant colonies in each library were specific for the appropriate phase. Of 20 putative phase-specific cDNAs selected from each subtracted library, eight unique clones were obtained for the sporophyte and seven for the gametophyte. After confirming their phase-specificities by hybridization to gametophyte and sporophyte messenger RNA, these 15 phase-specific cDNAs were sequenced, and the deduced amino acid sequences were used to search protein databanks. Two proteins encoded by the sporophyte-specific cDNAs and two by the gametophyte-specific cDNAs were identified by their similarity to databank entries.     

An ''equalized cDNA library'' by the reassociation of short double-stranded cDNAs.

The total number of genes in higher organisms is estimated to be under one hundred thousand. However, constructing a cDNA library containing a full set of genes expressed throughout the life time of an organism, without redundancy, is a major challenge for modern biology. Towards this goal, I have tried to make a library of mouse fibroblastoid Ltk- cells with nearly equal representations of cDNA clones. Double-stranded cDNAs (ds-cDNAs) are synthesized from mRNA using an oligo(dT)-Notl primer. After shearing to 200-400 bp, a synthetic linker-primer, which has one blunt and one sticky end and an internal EcoRl site, is ligated to the cDNAs. The cDNAs are amplified by the polymerase chain reaction (PCR) using the ligated linker-primer sequence. After denaturation and reassociation of the ds-cDNAs, and isolation of single-stranded cDNAs (ss-cDNAs) by hydroxylapatite chromatography, the ss-cDNAs are again amplified by PCR. The cDNAs are digested with EcoRl and Notl, and inserted into a plasmid vector. Colony hybridization with eight probes of different abundance showed a reduction in 'abundance variation' from at least 20,000-fold in the original library to 40-fold in the library constructed after three cycles of equalization. This indicates the usefulness of the current procedure for making equalized cDNA libraries.     

Expression cloning of oncogenes by retroviral transfer of cDNA libraries.

a cDNA library transfer system based on retroviral vectors has been developed for expression cloning in mammalian cells. The use of retroviral vectors results in stable cDNA transfer efficiencies which are at least 100-fold higher than those achieved by transfection and therefore enables the transfer and functional screening of very large libraries. In our initial application of retroviral transfer of cDNA libraries, we have selected for cDNAs which induce oncogenic transformation of NIH 3T3 fibroblasts, as measured by loss of contact inhibition of proliferation. Nineteen different transforming cDNAs were isolated from a total of 300,000 transferred cDNA clones. Three of these cDNAs were derived from known oncogenes (raf-1, lck, and ect2), while nine others were derived from genes which had been cloned previously but were not known to have the ability to transform fibroblasts (beta-catenin, thrombin receptor, phospholipase C-gamma 2 and Spi-2 protease inhibitor genes). The Spi-2 cDNA was expressed in antisense orientation and therefore is likely to act as an inhibitor of an endogenous transformation suppressor. Seven novel cDNAs with transforming activities, including those for three new members of the CDC24 family of guanine nucleotide exchange factors, were also cloned from the retroviral cDNA libraries. Retroviral transfer of libraries should be generally useful for cloning cDNAs which confer selectable phenotypes on many different types of mammalian cells.     

Characterization of size-fractionated cDNA libraries generated by the in vitro recombination-assisted method.

We here modified a previously reported method for the construction of cDNA libraries by employing an in vitro recombination reaction to make it more suitable for comprehensive cDNA analysis. For the evaluation of the modified method, sets of size-selected cDNA libraries of four different mouse tissues and human brain were constructed and characterized. Clustering analysis of the 3' end sequence data of the mouse cDNA libraries indicated that each of the size-fractionated libraries was complex enough for comprehensive cDNA analysis and that the occurrence rates of unidentified cDNAs varied considerably depending on their size and on the tissue source. In addition, the end sequence data of human brain cDNAs thus generated showed that this method decreased the occurrence rates of chimeric clones by more than fivefold compared to conventional ligation-assisted methods when the cDNAs were larger than 5 kb. To further evaluate this method, we entirely sequenced 13 human unidentified cDNAs, named KIAA1990-KIAA2002, and characterized them in terms of the predicted protein sequences and their expression profiles. Taking all these results together, we here conclude that this new method for the construction of size-fractionated cDNA libraries makes it possible to analyze cDNAs efficiently and comprehensively.     

Isolation of diallyl trisulfide inducible differentially expressed genes in human gastric cancer cells by modified cDNA representational difference analysis

Extensive epidemiologic studies indicated protective effects of consumption of garlic on reducing human gastric cancer (HGC) incidence. Diallyl trisulfide (DATS), a critical organic allyl sulfur component of garlic, was reported to have chemopreventive effects in inhibiting tumor process. We used DATS to treat HGC cell line BGC823 cells, and showed that DATS induces G1/S arrest and apoptosis in BGC823 cells demonstrated by a flow cytometric analysis. To further isolate DATS inducible differentially expressed genes in BGC823 cells, we combined a highly specific subtractive hybridization of cDNA representational difference analysis (cDNA RDA) with a sensitive bidirectional radioactive detection of mRNA differential display (mRNA DD) to develop a subtractive hybridization differential display (SHDD) method. This modified method adopted a first round of bidirectional subtractive hybridization between two sample cDNAs and a second round of bidirectional subtractive hybridization between the two resultant first-round difference products. Bidirectional subtractive hybridizations magnified the differences between the two sample cDNAs and favored isolating mRNA species with very small expression differences. We employed the SHDD method to detect DATS inducible differentially expressed genes in BGC823 cells. A total of 14 cDNA fragments (11 upregulated and 3 downregulated by DATS treatment) were isolated and confirmed by reverse Northern blot analysis. Our data show that SHDD is a powerful technique for identifying differentially expressed mRNA species between two sample cDNAs and provide useful cellular and molecular information for understanding the effects of garlic against human gastric cancer.     

Representational difference analysis using minute quantities of DNA.

Representational difference analysis (RDA) is a differential hybridization method which can effectively isolate unique DNA sequences from complex and highly related genomes or cDNA libraries. A major drawback of the RDA analysis is the requirement for pure driver and relatively pure tester samples, ruling out the analysis of whole tissue biopsies. To circumvent this problem, we have modified the technique for the analysis of very small quantities of DNA so that pure cell populations isolated by micromanipulation from tissue sections can be analyzed. Using this modified technique, as few as 50 diploid cells ( approximately 500 pg of DNA) can be analyzed.