title: Biologically relevant effects of mRNA amplification on gene expression profiles.
abstract: BACKGROUND
  Gene expression microarray technology permits the analysis of global gene expression profiles. The amount of sample needed limits the use of small excision biopsies and/or needle biopsies from human or animal tissues. Linear amplification techniques have been developed to increase the amount of sample derived cDNA. These amplified samples can be hybridised on microarrays. However, little information is available whether microarrays based on amplified and unamplified material yield comparable results. In the present study we compared microarray data obtained from amplified mRNA derived from biopsies of rat cardiac left ventricle and non-amplified mRNA derived from the same organ. Biopsies were linearly amplified to acquire enough material for a microarray experiment. Both amplified and unamplified samples were hybridized to the Rat Expression Set 230 Array of Affymetrix.
  
  
  RESULTS
  Analysis of the microarray data showed that unamplified material of two different left ventricles had 99.6% identical gene expression. Gene expression patterns of two biopsies obtained from the same parental organ were 96.3% identical. Similarly, gene expression pattern of two biopsies from dissimilar organs were 92.8% identical to each other.Twenty-one percent of reporters called present in parental left ventricular tissue disappeared after amplification in the biopsies. Those reporters were predominantly seen in the low intensity range. Sequence analysis showed that reporters that disappeared after amplification had a GC-content of 53.7+/-4.0%, while reporters called present in biopsy- and whole LV-samples had an average GC content of 47.8+/-5.5% (P <0.001). Those reporters were also predicted to form significantly more (0.76+/-0.07 versus 0.38+/-0.1) and longer (9.4+/-0.3 versus 8.4+/-0.4) hairpins as compared to representative control reporters present before and after amplification.
  
  
  CONCLUSIONS
  This study establishes that the gene expression profile obtained after amplification of mRNA of left ventricular biopsies is representative for the whole left ventricle of the rat heart. However, specific gene transcripts present in parental tissues were undetectable in the minute left ventricular biopsies. Transcripts that were lost due to the amplification process were not randomly distributed, but had higher GC-content and hairpins in the sequence and were mainly found in the lower intensity range which includes many transcription factors from specific signalling pathways.
authors.affiliation: BiGCaT Bioinformatics, University of Maastricht and Technical University Eindhoven, Maastricht, The Netherlands. rachel.vanhaaften@bigcat.unimaas.nl
authors.forename: Rachel I M
authors.initials: RI
authors.lastname: van Haaften
authors.forename: Blanche
authors.initials: B
authors.lastname: Schroen
authors.forename: Ben J A
authors.initials: BJ
authors.lastname: Janssen
authors.forename: Arie
authors.initials: A
authors.lastname: van Erk
authors.forename: Jacques J M
authors.initials: JJ
authors.lastname: Debets
authors.forename: Hubert J M
authors.initials: HJ
authors.lastname: Smeets
authors.forename: Jos F M
authors.initials: JF
authors.lastname: Smits
authors.forename: Arthur
authors.initials: A
authors.lastname: van den Wijngaard
authors.forename: Yigal M
authors.initials: YM
authors.lastname: Pinto
authors.forename: Chris T A
authors.initials: CT
authors.lastname: Evelo
mesh_terms: D000818:Animals; D016477:Artifacts; D003198:Computer Simulation; D020869:Gene Expression Profiling / Q000379:methods*; D017930:Genes, Reporter; D006352:Heart Ventricles / Q000378:metabolism*; D008957:Models, Genetic; D015233:Models, Statistical; D021141:Nucleic Acid Amplification Techniques / Q000379:methods*; D020411:Oligonucleotide Array Sequence Analysis / Q000379:methods*; D012333:RNA, Messenger / Q000235:genetics*; D051381:Rats; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014157:Transcription Factors / Q000235:genetics*
chemical_list: D012333:RNA, Messenger; D014157:Transcription Factors