In multi-cellular organisms, cells from different tissues have dramatically different phenotypes, even though they share the same genetic information. Until recently, phenotype diversity was thought to be largely the result of transcriptional regulation, different sets of genes being expressed in different cell types or at different developmental stages. It therefore came as a surprise that the human genome contains around 40,000 genes, only about twice as many as the genome of the worm Caernorhabditis elegans (The C.elegans sequencing consortium 1998). Probing the mammalian transcriptome with high-throughput sequencing techniques revealed that the key to this puzzle resides - at least partially - in the increased complexity of gene structure in mammalian genomes. 60% of human (Lander et al. 2001) and mouse (Zavolan et al. 2003) multi-exon genes have splice variants compared to only 22% of worm genes, although some authors argued that this is due to deeper coverage of mammalian compared to worm transcriptome (Brett et al. 2002). Another surprising finding of full-length cDNA sequencing studies is that mammalian genes frequently initiate transcription from different promoters, and that there are multiple polyadenylation sites for a given gene. Thus, in eukaryotes, the one gene - one protein paradigm of molecular biology turns out to be the exception rather than the rule, and various molecular mechanisms contribute to transcriptome diversification.
|Title of host publication||Computational and Statistical Approaches to Genomics|
|Number of pages||30|
|ISBN (Print)||0387262873, 9780387262871|
|Publication status||Published - Jan 1 2006|
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