We reviewed here putative functional roles of introns in various cellular processes such as splicing, mRNA transport, NMD, and expression regulation. Besides, introns may give some advantages as a mutational buffer in eukaryotic genomes protecting coding sequences from being affected by randomly occurring deleterious mutations. Introns occupy about 40% on average of the total length of genes, which means that most randomly occurring mutations will fall into intron regions, and do not affect protein sequences and functions. However, it is not clear how extensively and strongly this buffering effect of intron regions might have evolutionary advantages for intron retention against the pressure of removing cellular burdens.
