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Cell polarization and fusion are crucial developmental processes that occur in response to intracellular and extracellular signals. Asexual spores (conidia) of the mold Neurospora crassa differentiate two types of polarized cell protrusions, germ tubes and conidial anastomosis tubes (CATs), which exhibit negative and positive chemotropism, respectively. We provide the first evidence that shared and separate functions of the Rho-type GTPases CDC-42 and RAC-1 regulate these opposite chemotropisms. We demonstrate that RAC-1 is essential for CAT formation and cell fusion, whereas CDC-42 is necessary and sufficient for normal germ tube development. Cdc42-Rac-interactive-binding (CRIB) reporters were constructed to exclusively label locally activated GTP-bound GTPases. Time course analyses showed that repositioning of these activated GTPase clusters within germ tube and CAT tip apices controls directional growth in the absence of a tip-localized vesicle supply center (Spitzenkörper). We propose a model in which the local assembly of a plasma-membrane-associated GTPase-PAK-MAPK signaling platform regulates chemoattractant perception and secretion in order to synchronize oscillatory cell-cell communication and directional CAT tip growth.

Original publication

DOI

10.1242/jcs.141630

Type

Journal article

Journal

J Cell Sci

Publication Date

01/05/2014

Volume

127

Pages

1953 - 1965

Keywords

CDC-42, CRIB, Cell fusion, Chemotropism, Conidial anastomosis tube, Directional tip growth, Neurospora crassa, RAC-1, Cell Polarity, Chemotaxis, Neurospora crassa, Signal Transduction, cdc42 GTP-Binding Protein, rac GTP-Binding Proteins