The study by Binder, Frankfurter, and Rebhun investigates the distribution of tau, a microtubule-associated protein, in the mammalian central nervous system. Using a monoclonal antibody that binds to all tau polypeptides in both bovine and rat brains, they found that tau is more abundant in white matter extracts and microtubules compared to gray matter regions. Biochemical and immunocytochemical analyses revealed that tau is primarily localized in axons, as evidenced by its absence in glial cells. The monoclonal antibody Tau-1, which binds to all tau polypeptides, was used to demonstrate that tau is predominantly found in axons. The results suggest that tau may define a subpopulation of microtubules restricted to axons, and the antibody could be useful for studying axonal sprouting and growth. The study also highlights the differential localization of tau and MAP2, with tau being more abundant in axons and MAP2 in dendrites and cell bodies. These findings provide insights into the functional roles of tau in axonal microtubules and its potential importance in neuronal development and function.The study by Binder, Frankfurter, and Rebhun investigates the distribution of tau, a microtubule-associated protein, in the mammalian central nervous system. Using a monoclonal antibody that binds to all tau polypeptides in both bovine and rat brains, they found that tau is more abundant in white matter extracts and microtubules compared to gray matter regions. Biochemical and immunocytochemical analyses revealed that tau is primarily localized in axons, as evidenced by its absence in glial cells. The monoclonal antibody Tau-1, which binds to all tau polypeptides, was used to demonstrate that tau is predominantly found in axons. The results suggest that tau may define a subpopulation of microtubules restricted to axons, and the antibody could be useful for studying axonal sprouting and growth. The study also highlights the differential localization of tau and MAP2, with tau being more abundant in axons and MAP2 in dendrites and cell bodies. These findings provide insights into the functional roles of tau in axonal microtubules and its potential importance in neuronal development and function.