The acquisition of cell type-specific morphologies is a central feature of
neuronal differentiation. Many extra- and intracellular signals are known t
o cause the morphological changes of neuronal cells through the reconstruct
ion of the microfilaments underneath the cell membrane. The membrane microd
omain called "raft" has been paid much attention, for this domain contains
many signal-transducing molecules including trimeric G proteins and cytoske
letal proteins. The raft domain is recovered in a low-density fraction afte
r the treatment of the membrane with the non-ionic detergent such as Triton
X-100 and the enrichment of cholesterol and sphingolipids is ascribed to b
e responsible for the detergent insolubility. In contrast to the well-known
localization of trimeric G proteins in raft. the localization of small G p
roteins in the raft is poorly characterized. Since Rho family small G prote
ins (Rho. Rac. and Cdc42) regulate the microfilament system. we studied the
localization of Rho family small G proteins in the raft of rat brain with
western blotting. Specific localization of Rad was detected in the raft fro
m 10-day-old and 8-week-old rat whole brain, and also in the raft prepared
from the growth cone and synaptic plasma membrane fractions. Rho and Cdc42
were. in contrast, recovered in the Triton soluble fraction. Double immunos
taining of cultured hippocampal neurons with antibodies to Rad and MAP-2, o
r Rad and tau, showed punctate distribution of Rad in axons as well as in d
endrites. (C) 2001 Elsevier Science Ireland Ltd and the Japan Neuroscience
Society. All rights reserved.