DIFFERENTIAL EXPRESSION OF EXON-10 AND EXON-11 IN NORMAL TAU AND TAU ASSOCIATED WITH PAIRED HELICAL FILAMENTS

Antibodies were raised to two synthetic peptides with amino acid seque nces encoded by a variable region of exons 10 and 11 of the tau gene. The affinity-purified antibodies, designated E-10 and E-11, were used to determine whether PHF-tau and normal tau differ in variants contain ing three or four repeats in the microtubule-binding domain, respectiv ely. Normal adult human brain was shown by gel electrophoresis to cont ain six isoforms of tau. All of the isoforms reacted with E-11, wherea s only four of them with slower electrophoretic mobility were recogniz ed by E-10. Fetal brain tau was readily recognized by E-11 but reacted poorly with E-10. In PHF preparations, E-11 bound to all three polype ptides of PHF-tau of 68 kD, 64 kD, and 60 kD and reacted intensely wit h a material smearing from the top of the gel to about the 50-kD regio n. In contrast, E-10 only weakly recognized the two higher molecular w eight PHF-tau polypeptides of 68 kD and 64 kD), as well as smeared mat erial, and the binding was not affected by phosphatase treatment. Usin g recombinant tau with four repeats as a reference, the immunoreactivi ty of E-10 with PHF-tau was estimated to be approximately 5% of that o f E-11. By comparison, the immunoreactivity of E-10 with four isoforms of normal tan was comparable to that of E-11. These results indicate that the ratio of three vs. four repeat variants in PHF-tau is higher than in normal tau and suggest that Alzheimer disease may be associate d with the disproportional expression of fetal (or juvenile) forms of tau. Alternatively, the weak reactivity of PHF-tau with E-10 antibody could be due to post-translational modifications other than phosphoryl ation. (C) 1995 Wiley-Liss, Inc.