Quantitative analysis of gene expression by ion-pair high-performance liquid chromatography

Quantification of the levels of CYP2D6 mRNA in peripheral blood leukocytes by reverse transcriptase polymerase chain reaction HPLC

We developed a sensitive high performance liquid chromatography (HPLC) method for determining CYP2D6 mRNA in peripheral blood leukocytes (PBL) by using competitive reverse transcriptase polymerase chain reaction (RT-PCR). The method is specific, reproducible, and sensitive enough to quantify the absolute amount of low and high abundant CYP2D6 mRNA. The native CYP2D6 transcript and the internal standard, a CYP2D6 deletion RNA, were amplified with similar efficiency in RT-PCR. The PCR products were separated as the corresponding peaks in optimized HPLC. The coefficients of variation for competitive RT-PCR and HPLC determination were 1.5-6.5% and 0.6-2.4%, respectively, showing high reproducibility and reliability. This approach could also be applicable to the quantification of mRNA expressing on various tissues, including PBL, of which the expression levels were so low that they were hard to determine by existing agarose gel electrophoresis methods.

Synthesis and characterization of the oxidized dGTP lesions spiroiminodihydantoin-2'-deoxynucleoside-5'- triphosphate and guanidinohydantoin-2'-deoxynucleoside-5'- triphosphate

Two convenient synthetic routes to the oxidized guanosine triphosphate lesions spiroiminodihydantoin-2'-deoxynucleoside-5'-triphosphate (dSpTP) and guanidinohydantoin-2'-deoxynucleoside-5'-triphosphate (dGhTP) are reported. Both two-electron oxidation of 2'-deoxy-7,8-dihydro-8-oxoguanosine-5'-triphosphate (dOGTP) using SO4*- generated photolytically from K2S2O8 or four-electron oxidation of 2'-deoxyguanosine-5'-triphosphate (dGTP) from singlet oxygen provide either dSpTP or dGhTP at pH 8.0 or 4.4, respectively. Highly purified triphosphates are obtained by ion pair reversed-phase HPLC.

Identification and characterisation of clonal incomplete T-cell-receptor Vdelta2-Ddelta3/Ddelta2-Ddelta3 rearrangements by denaturing high-performance liquid chromatography and subsequent fragment collection: implications for minimal residual disease monitoring in childhood acute lymphoblastic leukemia

Incomplete T-cell-receptor delta (TCR-delta) rearrangements are widely used for detection of minimal residual disease in childhood acute lymphoblastic leukemia. In a substantial number of cases both alleles are rearranged and polymerase chain reaction (PCR) products have either to be cloned or excised and reamplified from acrylamide gels. Here we describe a novel HPLC-based method for identification and characterization of clonal TCR-delta targets. Clonality of PCR amplified TCR-delta products was examined on a high-resolution micropellicular DNASep matrix (WAVE Nucleic Acid Fragment Analysis System, Transgenomic) and subsequently classified into clonal, biclonal or negative samples. Vdelta2-Ddelta3 and Ddelta2-Ddelta3 rearrangements were analyzed by denaturing high-performance liquid chromatography (DHPLC), using triethylammonium acetate as an ion-pairing reagent, with a linear acetonitrile gradient at 50 degrees C. Biclonal elution profiles consisted of two individual homoduplex peaks and one heteroduplex peak unique for each patient sample. For characterization of biclonal rearrangements DHPLC separated samples were subjected to a second run and individual clonal peaks were collected. A software-controlled fragment collector was arranged in tandem with the HPLC system for this purpose and purified PCR products were collected in a time-dependent manner. Fractions were air dried and subsequently sequenced directly. The specificity of the observed patient specific sequences was tested via real time quantitative PCR on a LightCycler system.

Denaturing HPLC analysis of DNA deletions and insertions

Denaturing HPLC (DHPLC) is a useful technique for the fast screening of known and unknown heterozygous gene mutations. Most DNA mutations causing genetic disorders consist of nucleotide substitutions, but insertions and deletions occur, albeit less frequently. The heteroduplexes with insertions/deletions have gaps that may affect molecular stability differently from the mismatches caused by substitutions. Therefore, gaps and mismatches may be distinguished by DHPLC analysis, which is based on the differential thermal stability of amplicons with different characteristics. To verify this hypothesis, we examined 12 DNA samples containing insertions and deletions of different sizes (one to 29 residues) from four different genes (ABCA4, CFTR, FTL, and SLC11A3). We found that all of them were detected by DHPLC runs at 50 degrees C, which is considered a non-denaturing temperature, as well as by runs at the temperature optimized for mismatch recognition. The finding confirms that gaps reduce heteroduplex stability more than mismatches, and indicates that DHPLC analysis at low temperature may be applied to distinguish DNA deletions/insertions from substitutions.

The use of denaturing high-performance liquid chromatography (DHPLC) for the analysis of genetic variations: impact for diagnostics and pharmacogenetics

Over the past five years, denaturing high-performance liquid chromatography (DHPLC) has emerged as one of the most versatile technologies for the analysis of genetic variations. With the benefit of novel polymer chemistries used for separation, the accuracy, sensitivity, and the throughput of DHPLC for DNA and RNA analysis have greatly improved. DHPLC has been adopted in many laboratories for the screening of mutations and single-nucleotide polymorphisms (SNPs). The ability of DHPLC to detect known and unknown mutations simultaneously has put this technology at the forefront of genetic analysis for a wide variety of diseases. In addition, the high sensitivity of DHPLC combined with the accuracy of the heteroduplex analysis has allowed the development of applications beyond the scope of traditional sequencing or genotyping, e.g., the early detection of cancer. This article reviews the methods, which made DHPLC a widely used tool for diagnosis in molecular genetics and pharmacogenetics. The article provides an overview of current applications in these fields and points to novel applications in areas like epigenetics and the analysis of heteroplasmic mitochondrial DNA, in which DHPLC is becoming the leading technology.

Application of high-resolution capillary array electrophoresis with automated fraction collection for GeneCalling trade mark analysis of the yeast genomic DNA

Capillary array instrument was applied to transcript profiling of the yeast genomic DNA using GeneCalling trade mark chemistry. The instrument integrated a 12-capillary array for DNA separation with a replaceable sieving matrix, laser-induced fluorescence detection and an automated microfraction collector. The DNA fractions, exiting the separation capillaries, were continuously deposited in a 1536-well collection plate made of agarose gel. DNA fragments recovered from selected fractions were cloned and then sequenced. Over 80% of theoretically predicted fragments could be recovered in the collected fractions, cloned and sequenced with an average redundancy of threefold. Excellent correlation of the experimentally obtained sequences with the theoretically predicted gene fragments demonstrated the suitability of capillary array electrophoresis for micropreparative recovery of DNA fragments. This approach, useful especially for rapid DNA expression profiling of unknown genes for nonsequenced organisms, demonstrates the practical capability of the prototype multicapillary fraction collector.

A decade of high-resolution liquid chromatography of nucleic acids on styrene-divinylbenzene copolymers

The introduction of alkylated, nonporous poly-(styrene-divinylbenzene) microparticles in 1992 enabled the subsequent development of denaturing HPLC that has emerged as the most sensitive screening method for mutations to date. Denaturing HPLC has provided unprecedented insight into human origins and prehistoric migrations, accelerated the cloning of genes involved in mono- and polygenic traits, and facilitated the mutational analysis of more than a hundred candidate genes of human disease. A significant step toward increased sample-throughput and information content was accomplished by the recent introduction of monolithic poly(styrene-divinylbenzene) capillary columns. They have enabled the construction of capillary arrays amenable to multiplex analysis of fluorescent dye-labeled nucleic acids by laser-induced fluorescence detection. Hyphenation of denaturing HPLC with electrospray ionization mass spectrometry, on the other hand, has allowed the direct elucidation of the chemical nature of DNA variation and determination of phase of multiple alleles on a chromosome.

Flow Cytometric Quantification of Competitive Reverse Transcription-PCR Products

Background: Competitive PCR of reverse transcribed mRNA sequences is used to quantify transcripts, but the usual approaches are labor-intensive and time-consuming. We describe the non-gel-based quantification of competitive reverse transcription (RT)-PCR products with use of microparticles and flow cytometry.

Methods: PCR products of a target sequence and an internal control sequence (competitor) were labeled during PCR using digoxigenin (DIG)- and dinitrophenol (DNP)-labeled primer, respectively, allowing specific binding to microparticles coated with the corresponding antibody. Both amplification products were biotinylated to enable fluorescence labeling with streptavidin-R-phycoerythrin. The mean fluorescence intensity of each microparticle population, corresponding to the amount of bound PCR product, was measured in a flow cytometer. We constructed microparticles coated with antibodies against DIG and DNP to specifically capture PCR products derived from target and competitor sequences, respectively.

Results: As required for a reliable competitive PCR assay, nearly identical kinetics were found for the amplification of target and competitor sequences when using only one competitive primer. The method was applied to examine interleukin-8 expression in human lymphocytes after x-irradiation. One hour after irradiation, the concentration of transcripts decreased by half.

Conclusions: The flow cytometric assay for the quantification of competitive RT-PCR products avoids additional hybridization steps and antibody labeling. The use of paramagnetic microparticles would also enable the complete automation of this method.

Quantitative determination of gene expression in human lymphocytes assessed by reverse transcription-polymerase chain reaction coupled to high-performance liquid chromatography

Gene expression in human lymphocytes was assessed using reverse transcription and polymerase chain reaction amplification followed by ion-pair reversed-phase chromatography analysis. Competitive PCR was used to quantitate the desired cDNAs with a polivalent competitor adaptable to multiple novel mRNAs estimations with minor changes. Accuracy was 11.27+/- 11.87% (n = 7), as determined using standards. The coefficients of variation of the assessment of human OK12b were 7% (n = 6), 7.68 attmol/microg of total RNA, and 21% (n = 6), 0.93 attmol/microg of total RNA. Sample-to-sample variation in the reverse transcription and in the quantity and quality of RNA was attenuated by normalising results to beta-actin mRNA expression. The correlation between the OK12b/beta-actin ratio and competitive assessments of OK12b was 0.984, n = 6. The correlation between HPLC results and an independent method based on radionuclide uptake by the product, detected by electrophoretic separation, was 0.848, n = 10.

Denaturing high-performance liquid chromatography: A review

Denaturing high-performance liquid chromatography (DHPLC) compares two or more chromosomes as a mixture of denatured and reannealed PCR amplicons, revealing the presence of a mutation by the differential retention of homo- and heteroduplex DNA on reversed-phase chromatography supports under partial denaturation. Temperature determines sensitivity, and its optimum can be predicted by computation. Single-nucleotide substitutions, deletions, and insertions have been detected successfully by on-line UV or fluorescence monitoring within 2-3 minutes in unpurified amplicons as large as 1.5 Kb. Sensitivity and specificity of DHPLC consistently exceed 96%. These features and its low cost make DHPLC one of the most powerful tools for the re-sequencing of the human and other genomes. Aside from its application to the mutational analysis of candidate genes, DHPLC has proven instrumental in elucidating human evolution and in the mapping of genes. Employing completely denaturing conditions, the utility of DHPLC has been extended to the genotyping of known polymorphisms by utilizing the ability of poly(styrene-divinylbenzene) to resolve single-stranded DNA molecules of identical size that differ in a single base. Under completely denaturing conditions, it is thus possible to resolve all possible base substitutions with the single exception of C-->G transversions. Improvements in throughput became feasible with the recent introduction of monolithic poly(styrene-divinylbenzene) capillaries that lend themselves to the fabrication of arrays connected to a multi-color laser induced fluorescence scanner or a mass spectrometer.

Cyclophilin B expression in renal proximal tubules of hypertensive rats

Rat cyclophilin-like protein (Cy-LP) is a candidate hypertension gene initially identified by differential hybridization and implicated in renal mechanisms of salt retention and high blood pressure. We report the molecular characterization of rat cyclophilin B (CypB) and demonstrate, through sequence analysis and an allele-specific polymerase chain reaction primer assay, that CypB but not Cy-LP is expressed in rat kidney. CypB is an endoplasmic reticulum-localized prolyl-isomerase that interacts with elongation initiation factor 2-beta, an important regulator of protein translation and a central component of the endoplasmic reticulum stress response to hypoxia or ATP depletion. Active renal transport of sodium is increased in the spontaneously hypertensive rat (SHR), and there is evidence that this coincides with hypoxia and ATP depletion in the renal cortex. In the present studies we have examined expression of CypB in rat proximal tubules, which contributes to the increased renal sodium reabsorption in this model of hypertension. We report that CypB transcript abundance is significantly elevated in proximal convoluted tubules from SHR compared with the control Wistar-Kyoto strain. This upregulation occurs in weanling animals and precedes the development of hypertension, indicating that it is not a simple response to hypertension in SHR. Further, CypB expression is also higher in a proximal tubule cell line derived from SHR compared with a similar line derived from Wistar-Kyoto rats, indicating that this difference is genetically determined. No sequence differences were observed in the CypB cDNA from these 2 strains. These observations suggest that a genetically determined alteration in proximal tubules from SHR occurs that leads to increased expression of CypB. In view of evidence linking CypB to the regulation of elongation initiation factor-2, the upregulation of CypB may result from metabolic stress.

Altered sodium pump alpha and gamma subunit gene expression in nephron segments from hypertensive rats

OBJECTIVE

To determine the qualitative and quantitative expression of alpha and gamma sodium pump subunits in whole kidney and nephron segment RNA from Sprague Dawley rats, spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats.

DESIGN

A novel reverse transcription polymerase chain reaction technique was devised which provides accurate and precise measurement of the number of molecules of specific transcript abundance, a measurement of gene expression. This allows the quantitative comparison of multiple samples across multiple subjects and, since the estimates are accurate rather than relative, can also be used to make quantitative comparisons across expressed genes, such as isoforms and subunits of the heterotrimeric renal sodium pump.

METHODS

We examined which catalytic isoforms were expressed and then quantified transcript abundance in whole kidney and convoluted and straight segments of the proximal tubule.

RESULTS

Alpha 1 and gamma transcripts, but not alpha 2, alpha 3 or alpha 4 isoforms, were consistently observed in nephron segments. Levels of alpha 1 were lower in kidney RNA from 15-16-week-old SHR than in WKY rats of the same age (P = 0.001), but were not different between SHR and WKY in 4-5-week-old animals. No significant difference was observed in gamma subunit abundance in kidney RNA from 4-5-week-old animals; however, at 15-16 weeks, the expression in SHR was one-third that in WKY rats (P = 0.003). In proximal convoluted tubules from 4-5-week-old animals, the level of alpha 1 RNA expression was lower (P = 0.03) in SHR than in WKY rats. In addition, levels of alpha 1 in proximal straight tubule from the 4-5-week-old SHR were also lower than in WKY rats (P = 0.02). This difference was even greater in 15-16-week-old animals: in SHR, alpha 1 expression was less than 20% of the level of expression in WKY rats (P = 0.0003). Expression of the gamma subunit exhibited a similar pattern of downregulation in SHR. In RNA from proximal convoluted tubules and proximal straight tubules from both 4-5- and 15-16-week-old animals, expression of the gamma subunit was demonstrated to be significantly lower in SHR than in WKY rats.

CONCLUSION

The results indicate a coordinate reduction in the abundance of sodium pump alpha and gamma subunits in the proximal tubules of SHR, which occurs early during the development of hypertension.