314 Developmental Brain Research, 13 (1984) 314-318 Elsevier BRD 60011 MAP2 is localized to the dendrites of hippocampal neurons which develop in culture ALFREDO CACERES l,*, GARY BANKER 1, OSWALD STEWARD 2, LESTER BINDER 3 and MICHAEL PAYNE 4 1Department of Anatomy, Albany Medical College, Albany, NY 12208; 2Departments of Neurosurgery and Physiology, University of Virginia School of Medicine, Charlottesville, VA 22908; 3Departmentof Biology, Universityof Virginia, Charlottesville, VA 22903; and 4Departmentof Anatomy, New York Medical College, Valhalla, NY10595 (U.S.A.) (Accepted December 20th, 1983) Key words: microtubule-associated proteins - - cytoskeleton - - hippocampal neurons - - tissue culture - - dendrites - - neuronal development - - immunocytochemistry - - monoclonal antibodies The distribution of the microtubule-associated protein MAP2 in cultured hippocampal neurons was studied using immunocyto- chemistry with monoclonal antibodies. MAP2 was preferentially localized to dendritic, but not axonal, processes even in single isola- ted cells which developed without making intercellular contacts. Hence regional differences in the molecular composition of the neu- ronal cytoskeleton can develop independently of cell interactions. The presence of MAP2 may be a useful marker for identifying den- drites in cell culture. Neurons are unique among all cells of the body for the remarkably complex shapes attained by their ax- onai and dendritic processes. Neuronal shape is of critical functional importance because it determines the synaptic connections which a cell can establish and because it is inextricably linked with a selective distribution of the molecular constituents of the cell to particular regions of its axon or dendrites. The re- gional localization of such constituents as neurotrans- mitter receptors and ion channels gives the nerve cell a functional polarity and determines the detailed functional properties which distinguish one type of nerve cell from another. Both intrinsic and extrinsic factors have been im- plicated in determining the detailed shape of neu- r o n s 7A4.23.25. T h e information presently available strongly suggests that the cytoskeleton is one of the important endogenous determinants of cell shapel4, 25. Recently it has been shown that the two fundamentally different classes of neuronal process- es, axons and dendrites, differ in the molecular com- position of their microtubules. Certain of the high molecular weight microtubule-associated proteins (MAPs) 20, including in particular MAP211,12,26, are preferentially associated with dendritic microtu- bules. MAPs can control the rate of microtubule polymerization in vitro, and are thought to influence the stability of microtubules 22 and their interactions with other elements of the cytoskeleton9,13,18 in living cells. Axons and dendrites also differ in the molecu- lar composition of their neurofilaments15, 24. We have chosen to study the cytoskeletal organiza- tion of neurons in culture, where the distribution of specific cytoskeletal constituents can be studied in in- dividual cells and where the extent of cellular interac- tions can be controlled. It has been established that neurons from the rat hippocampus elaborate process- es in culture which can be distinguished as axons or dendrites based on their light microscopic appear- ance 3, their ultrastructural features 4 and their synap- tic polarityS. In the present study we have used im- munocytochemistry,to determine the distribution of MAP2 in hippocampal neurons in culture in order to answer the following questions. Does MAP2 become preferentially localized to the dendritic compartment of the cell even when the spatial and temporal pat- * Permanent address: Instituto de Investigacion Medica Mercedes y Martin Ferreyra, Casilla de Correo 389, 5000 Cordoba, Argenti- na, Correspondence: G. Banker, Department of Anatomy, Albany Medical College, Albany, NY 12208, U.S.A. 0165-3806/84/$03.00 © 1984 Elsevier Science Publishers B.V.