CDC-42 and RAC-1 regulate opposite chemotropisms in Neurospora crassa.
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.
Institute of Cell Biology, University of Edinburgh, Mayfield Road, Edinburgh EH9 3JR, Scotland, UK.
Alexander
A
Lichius
Andrew B
AB
Goryachev
Mark D
MD
Fricker
Boguslaw
B
Obara
Ernestina
E
Castro-Longoria
Nick D
ND
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D016764:Cell Polarity / Q000235:genetics / Q000502:physiology; D002633:Chemotaxis / Q000235:genetics / Q000502:physiology; D009492:Neurospora crassa / Q000378:metabolism*; D015398:Signal Transduction; D020764:cdc42 GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*; D020744:rac GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*
D020764:cdc42 GTP-Binding Protein; D020744:rac GTP-Binding Proteins
CDC-42; CRIB; Cell fusion; Chemotropism; Conidial anastomosis tube; Directional tip growth; Neurospora crassa; RAC-1