Immunohistochemical study of microtubule-associated protein 5 (MAP5) expression in the developing human brain.

The expression of microtubule-associated protein 5 (MAP5) in the developing human brain was studied by means of an immunohistochemical method. In the cerebellum, MAP5 immunoreactivity appeared in the molecular layer and subcortical white matter from the early fetal age of 13 gestational weeks (GW), and temporally increased in the outer halves of the molecular layer and subcortical white matter at 36 GW to 2 months of age and 20 to 22 GW, respectively. In the cerebrum, it already appeared in the molecular layer and subcortical white matter from 13 GW, and was marked at 20 to 26 GW and 24 to 32 GW, respectively. Cortical pyramidal neurons gradually became immunoreactive from 28 GW to adolescence. Ependymal cilia were markedly positive in ventricular wall in all ages. In Western blot analyses, MAP5 showed two separate molecular weight bands. In the fetal period 320 kDa protein was prominent, but 300 kDa protein could be detected only at 11 years of age. Thus MAP5 was markedly expressed in growing axon in the fetal period and may be essential for the elongation and maturation as well as the function maintenance of axons and dendrites in developing human brain.