Transcriptomic approaches to toxicity assessment

‘Omics’ technologies, such as the study of genomes (‘genomics’), proteomes (‘proteomics’) and metabolites (‘metabolomics’), are widely applied in a diverse range of biological disciplines. Furthermore, the ready availability of entire genome sequences from humans and many other organisms has resulted in numerous studies to understand gene functions (1). In gene function studies, gene expression is generally viewed as the expression of transcripts that encode the fi nal product of proteins. Transcripts globally expressed from the genome are called the transcriptome: the mRNAs produced as a result of transcription from individual genes are called transcripts, while the entire array of mRNAs transcribed from all genes (i.e., genome) is called the transcriptome; the study of transcriptomes is called transcriptomics (2). The fi nal protein products globally expressed from genomes are called proteomes (3). The transcriptomes and proteomes are collectively referred to as expressomes, and global assessment of expressomes is called expressomics.