The enrichment and complexity of the transcriptome in the human brain are accompanied by high—compared to others tissues—magnitudes and levels of alternative splicing, the process by which the exons (the portions of the gene coding for protein) of a gene are reconnected in multiple ways producing different forms of mature RNA (de la Grange, et al., 2010; Mortazavi, et al., 2008; E. T. Wang, et al., 2008; Yeo, Holste, Kreiman, & Burge, 2004). Using data from public transcript databases corresponding to 800 cDNA library sources, Yeo and colleagues (Yeo, et al., 2004) assessed the frequencies of genes containing skipped exons, i.e., genes containing alternative 3′ or 5′ splice site exons, which indicate which version of the gene needs to be transcribed (or not), that are shortened or lengthened due to alternative splicing, across a sample of 16 human tissues. Unusually high levels of all these alternative splicing events were found in the human liver, testes and brain. Additionally these particular human tissues have highly distinct splicing patterns (or sets of spliced isoforms) that differ from most other tissues. Another study
