Journal of Neuroscience, Vol 8, 4503-4512, Copyright © 1988 by Society for Neuroscience
The sequential appearance of low- and high-molecular-weight forms of MAP2 in the developing cerebellum
RP Tucker, LI Binder, C Viereck, BA Hemmings and AI Matus
Friedrich Miescher Institute, Basel, Switzerland.
Mammalian microtubule-associated protein 2 (MAP2) exists in high-
molecular-weight (Mr approximately 280,000) and low-molecular-weight (Mr
approximately 70,000) forms, with the latter protein being more abundant in
embryonic brain homogenates than in preparations from mature brain
(Riederer and Matus, 1985). In the current study, we have shown that avian
MAP2 also exists as both high- (Mr approximately 260,000) and
low-molecular-weight (Mr approximately 65,000) forms whose relative
abundance changes during brain maturation, indicating a conserved function
for these proteins during vertebrate neuronal morphogenesis. Using indirect
immunohistochemistry, we have determined the cellular distribution of the
high- and low-molecular-weight forms of MAP2 in the developing avian
cerebellum. In the embryonic cerebellum, low-molecular-weight MAP2 is found
in the external granular layer and in epithelial cells.
High-molecular-weight MAP2 is found only in neurons that have commenced
dendrogenesis, i.e., Purkinje cells and neurons within the internal
granular layer. Thus, low-molecular-weight MAP2 is not only more abundant
in embryonic nervous tissue than in the adult, but it also appears in glia
and in differentiating neurons before the high-molecular-weight form. We
have also shown that in the mature cerebellum high-molecular-weight MAP2
cannot be detected with monoclonal antibodies or polyclonal antisera in
Purkinje cell dendrites. Polyclonal antisera against the regulatory subunit
of the cAMP-dependent protein kinase, which is associated with MAP2 in the
Purkinje cell dendrites of the rat, also fail to stain Purkinje cell
dendrites in the mature quail cerebellum. This suggests that high-
molecular-weight MAP2 may be necessary for the establishment of dendrites
but is not necessary for the maintenance of dendritic form.