Journal of Cell Science 116, e705-e705 (2003)
Copyright © 2003 The Company of Biologists Limited
Rac — a passport to complexity
Rho-family GTPases, such as Rho, Rac and Cdc42, are essential cytoskeletal
regulators in higher eukaryotes, controlling reorganization of the actin
network and polarized cell growth. Rho and Cdc42 are also present in S.
cerevisiae and S. pombe. By contrast, Rac, which is implicated
in control of lamellipodium formation and cell morphology, has no orthologue
in these organisms. Why is this? Alex Andrianopoulos and co-workers provide a
clue, identifying a Rac orthologue (CflB) in Penicillium marneffei
— a fungus that switches between uninucleate yeast and multinucleate
hyphal forms (see p. 1249).
They show that CflB colocalizes with actin at septation sites and the tips of
vegetative hyphal cells. Furthermore, by generating strains that express
activated or dominant negative CflB (or lack it entirely), they demonstrate
that the GTPase is necessary for cell polarization during hyphal growth but
not yeast growth — unlike the Cdc42 orthologue, CflA. The authors also
observe that CflB (but not CflA) is required for morphogenesis of
conidiophores — complex multicellular structures that appear during
asexual development of P. marneffei. The Rac GTPase thus appears to
complement Cdc42 by providing aspects of polarity control associated with
increasing cellular complexity.
Related articles in JCS:
- Control of morphogenesis and actin localization by the Penicillium marneffei RAC homolog
- Kylie J. Boyce, Michael J. Hynes, and Alex Andrianopoulos
JCS 2003 116: 1249-1260.
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