Developmental expression of a 56 kDa protein isolated from rat neocortex

The expression of ALZ-50 immunoreactivity in the immature rat cortex was assessed using a variety of immunochemical techniques. The antigen recognized by ALZ-50 was isolated using immunoaffinity column chromatography. Unlike the ALZ-50-positive antigen found in the brains of people with Alzheimer's Disease (mol. wt. 68 kDa), the principal antigen expressed in the immature rat had a molecular weight of 56 kDa. The temporal expression of ALZ-50-positive antigens was determined with immunoblotting techniques. The expression of the 56 kDa protein appeared during the last prenatal week, increased to a peak during the second postnatal week and waned in the third postnatal week. Immunohistochemically, neonatal cortex contained many ALZ-50-positive neurons in the cortical subplate and the intermediate zone and a smattering of neurons in the cortical plate. The temporal expression of the ALZ-50-positive 56 kDa antigen was similar to that for fetal tau (tau-1); however, the principal protein identified by the anti-tau-1 antibody was considerably larger (being about 68-70 kDa). In contrast to ALZ-50, tau-1-immunoreactive elements were distributed in the subplate, the deep cortical plate, the intermediate zone and the subventricular zone. tau-1-positive axons passing through the superficial intermediate zone were conspicuous. Thus, the biochemical and anatomical evidence show that ALZ-50 and tau-1 recognize distinct proteins.