The gene, mRNA and protein isoforms of tau. In tau genomic structure (top panel), the black boxes represent constitutive exons, and the gray and empty boxes represent alternative spliced exons. The middle panel demonstrates mRNAs of tau in adult human brain. A total six mRNAs are generated by alternative splicing of exons 2, 3 and 10, which is indicated by alternative lines linking these exons. The lower panel shows six isoforms of tau in adult human brain. Gray boxes represent the N-terminal inserts (coded by exons 2 and 3) or MT-binding repeats (coded by exons 9, 10, 11 and 12). The second MT-binding repeat coded by exon 10 is highlighted by dark gray box. The commonly used terms for each tau isoform are listed at the right side of the isoforms.