Transcriptome and Proteome Analysis using Signature Tags

Sammanfattning: With the full sequence of the human genome now available, anexciting era in biomedical research has started. The sequenceprovides information about all our genes and greatly increasesthe scope to compare genetic activities in different cells, toanalyze genetic variation between individuals and betweendifferent species and, most importantly, to investigatesystematically the whole genome in a gene-by-gene manner, andthus increase our understanding of gene function.This thesis describes studies in which developments weremade in several areas of functional genomics. Messenger RNAlevels were analyzed by the use of an amplification procedure,in which the 3´-ends of the transcripts were selected inorder to amplify the mRNA population in an unbiased fashion. Bysonicating cDNA originating from expressed mRNA, uniformlysized representatives of the transcripts,?signaturetags?, were obtained. The mRNA levels in the original mRNApopulation correlated well with the levels in the amplifiedmaterial, as verified by microarray analysis and realtimequantitative PCR. The expressed transcripts can be identifiedusing pyrosequencing, by comparing the obtained sequenceinformation from the signature tags to information contained invarious sequence databases. In one of the articles, the use ofpyrosequencing is illustrated by efforts to find genes involvedin the disease progression of atherosclerosis.More challenging than the study of mRNA levels is to analyzewhen, where and how proteins fulfill their wide-ranging rolesin all the various cellular processes. Proteins are morecomplex biomolecules than mRNA, each having unique properties.Current techniques for studying proteins need much improvement,and are often limited to investigations of a specific portionof the proteome. One approach for studying the whole proteomeis to systematically generate reagents with specific affinityfor the proteins encoded by the genome, one by one. Theaffinity reagents can be used as flags for their targets,providing a flag-specific detection system, so that the targetproteins can be sub-cellularly localized in the majority ofhuman tissues in an array format. One of the articles includedin the thesis presents a pilot project for large-scale affinityreagent production. The aim was to provide a sound basis forwhole proteome studies, but as a pilot study this investigationwas limited to the proteins encoded by human chromosome 21. Allputative genes on the chromosome were subjected to antibodygeneration in a systematic manner. Small, uniform, and easilyproduced representative portions of the full-length proteinswere expressed. These were denoted?Protein EpitopeSignature Tags?and were designed to be unique for theirfull-length counterparts. The antibodies were produced inrabbits and two of the articles in the thesis discuss differentapproaches for affinity purification of the antibodies toachieve the highest possible specificity towards the targets.The resulting?mono-specific?, but still?multi-epitope?, antibodies can be used for a widerange of additional biochemical studies, such as protein arrayand protein pull-out analyses.Keywords:functional genomics, 3´-end signaturetags, pyrosequencing, amplification, PrEST, chromosome 21,polyclonal antibodies, dual expression, affinitypurification.