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J. Cell Biol.,
Volume 142, Number 3, August 10, 1998 815-825
* Cell Adhesion Unit, Department of Biological and Technological Research, San Raffaele Scientific Institute, 20132 Milano,
Italy; and Rho family GTPases have been implicated in
cytoskeletal reorganization during neuritogenesis. We
have recently identified a new gene of this family,
cRac1B, specifically expressed in the chicken developing nervous system. This GTPase was overexpressed in
primary neurons to study the role of cRac1B in the development of the neuronal phenotype. Overexpression
of cRac1B induced an increment in the number of neurites per neuron, and dramatically increased neurite
branching, whereas overexpression of the highly related and ubiquitous cRac1A GTPase did not evidently
affect neuronal morphology. Furthermore, expression
of an inactive form of cRac1B strikingly inhibited neurite formation. The specificity of cRac1B action observed in neurons was not observed in fibroblasts, where both GTPases produced similar effects on cell
morphology and actin organization, indicating the existence of a cell type-dependent specificity of cRac1B
function. Molecular dissection of cRac1B function by
analysis of the effects of chimeric cRac1A/cRac1B proteins showed that the COOH-terminal portion of
cRac1B is essential to induce increased neuritogenesis
and neurite branching. Considering the distinctive regulation of cRac1B expression during neural development, our data strongly support an important role of
cRac1B during neuritogenesis, and they uncover new
mechanisms underlying the functional specificity of distinct Rho family GTPases.
Institute of Hormone Chemistry, National Research Council, 20133 Milano, Italy
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