The study by Lester I. Binder, Anthony Frankfurter, and Lionel I. Rebhun investigates the biochemical and immunocytochemical localization of the heterogeneous microtubule-associated protein tau in bovine and rat brains. Using a monoclonal antibody that binds to all tau polypeptides, they found that tau is more abundant in white matter extracts and microtubules compared to gray matter. Immunohistochemical studies showed that tau is localized in axons, not in glia, indicating that tau is neuron-specific. These findings suggest that tau may define a subpopulation of microtubules restricted to axons. The monoclonal antibody developed in this study is useful for studying axonal sprouting and growth as it is an exclusive axonal marker. MAP2 and tau are both microtubule-associated proteins that stimulate microtubule assembly in vitro and bind along the entire length of the polymer. MAP2 is primarily found in dendrites and cell bodies, while tau is mainly in axons. Biochemical studies showed that tau is more electroproteically heterogeneous and varies in electrophoretic mobility during brain maturation, indicating posttranslational modifications. The immature forms of MAP2 and tau are less efficient in promoting microtubule assembly than their adult forms, suggesting that microtubules in immature brain are less stable. The study also found that tau is more abundant in white matter microtubules than in gray matter, and that tau is primarily localized in axons. Immunohistochemical studies confirmed that tau is restricted to axons, with no staining in cell bodies or dendrites. These findings support the idea that tau is predominantly axonal. The monoclonal antibody used in this study was developed to recognize all tau polypeptides in both bovine and rat brains and was used to demonstrate the localization of tau in axons. The study also highlights the importance of tau in the development and maturation of neurons, as the number and complexity of tau polypeptides change during postnatal development, paralleling changes in MAP2 and tubulin. The findings suggest that tau may play a role in the biochemical composition of axonal microtubules.The study by Lester I. Binder, Anthony Frankfurter, and Lionel I. Rebhun investigates the biochemical and immunocytochemical localization of the heterogeneous microtubule-associated protein tau in bovine and rat brains. Using a monoclonal antibody that binds to all tau polypeptides, they found that tau is more abundant in white matter extracts and microtubules compared to gray matter. Immunohistochemical studies showed that tau is localized in axons, not in glia, indicating that tau is neuron-specific. These findings suggest that tau may define a subpopulation of microtubules restricted to axons. The monoclonal antibody developed in this study is useful for studying axonal sprouting and growth as it is an exclusive axonal marker. MAP2 and tau are both microtubule-associated proteins that stimulate microtubule assembly in vitro and bind along the entire length of the polymer. MAP2 is primarily found in dendrites and cell bodies, while tau is mainly in axons. Biochemical studies showed that tau is more electroproteically heterogeneous and varies in electrophoretic mobility during brain maturation, indicating posttranslational modifications. The immature forms of MAP2 and tau are less efficient in promoting microtubule assembly than their adult forms, suggesting that microtubules in immature brain are less stable. The study also found that tau is more abundant in white matter microtubules than in gray matter, and that tau is primarily localized in axons. Immunohistochemical studies confirmed that tau is restricted to axons, with no staining in cell bodies or dendrites. These findings support the idea that tau is predominantly axonal. The monoclonal antibody used in this study was developed to recognize all tau polypeptides in both bovine and rat brains and was used to demonstrate the localization of tau in axons. The study also highlights the importance of tau in the development and maturation of neurons, as the number and complexity of tau polypeptides change during postnatal development, paralleling changes in MAP2 and tubulin. The findings suggest that tau may play a role in the biochemical composition of axonal microtubules.