EXPRESSION OF A PAIRED HELICAL FILAMENT TAU-EPITOPE IN EMBRYONIC CHICKEN CENTRAL-NERVOUS-SYSTEM

IMMUNOBLOTS from embryonic chicken optic lobes (midbrain) and spinal c ord were found to contain different proteins with a molecular weight b etween 45 and 70 kDa that are recognized by monoclonal antibodies (mAb s) directed at human tau proteins. Each appears as a doublet on SDS-PA GE. The upper, slower migrating bands were recognized by AT8, a monocl onal antibody that requires a phosphorylated Ser-202, an epitope speci fic for abnormally phosphorylated tau of paired helical filaments (PHF -tau) in Alzheimer brains. The corresponding faster migrating bands we re stained by the mAbs BT2 and tau-1, both requiring an epitope contai ning a non-phosphorylated Ser-202. Phosphatase treatment abolished bin ding of AT8 and induced an additional binding of tau-1 (and BT2) to th e upper bands. Thus, the data suggest that in embryonic chicken centra l nervous system Ser-202 occurs in a phosphorylated and in a non-phosp horylated state in several distinct tau isoforms.