Human Microtubule‐Associated Protein‐2c Localizes to Dendrites and Axons in Fetal Spinal Motor Neurons

: Microtubule‐associated protein‐2 (MAP‐2) functions to maintain neuronal morphology by promoting the assembly of microtubules. MAP‐2c is an alternately spliced form of MAP‐2, containing the first 151 amino acids of high‐molecular‐weight (HMW) MAP‐2 joined to the last 321 amino acids, eliminating 1,352 amino acids specific to HMW MAP‐2. A polyclonal antibody generated to the splice site of human MAP‐2c was used to determine its cellular localization. The MAP‐2c antiserum was depleted of any HMW MAP‐2 reactivity by absorption with HMW MAP‐2 fusion protein. Western blot analysis of human fetal spinal cord homogenates demonstrated that the antibody is specific for human MAP‐2c. MAP‐2c immunoreactivity was found in the perinuclear cytoplasm and processes of anterior motor neurons and large processes of the posterior column in sections from 22–24‐week human fetal spinal cord. Double‐label confocal microscopy was performed using the MAP‐2c polyclonal antibody and either a HMW MAP‐2 or a neurofilament protein (highly phosphorylated 160‐ and 200‐kDa protein) monoclonal antibody to identify these processes as dendrites or axons, respectively. HMW MAP‐2 and MAP‐2c colocalized in cell bodies and dendrites of anterior motor neurons, demonstrating for the first time the presence of native MAP‐2c within dendrites. In addition, immunoelectron microscopy showed MAP‐2c associated with microtubules in dendrites of motor neurons. MAP‐2c and the neurofilament proteins were found in axons of the dorsal and ventral roots. The presence of MAP‐2c within axons and dendrites suggests that MAP‐2c contributes to neuronal plasticity during human fetal development.