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Published 25 April 2005. doi:10.1083/jcb.200412145
The Rockefeller University Press, 0021-9525 $8.00
JCB, Volume 169, Number 2, 321-329
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Article

A developmentally regulated Na-H exchanger in Dictyostelium discoideum is necessary for cell polarity during chemotaxis



Hitesh Patel and Diane L. Barber

Department of Cell and Tissue Biology, University of California, San Francisco, San Francisco, CA 94143

Correspondence to Diane L. Barber: barber{at}itsa.ucsf.edu

Increased intracellular H+ efflux is speculated to be an evolutionarily conserved mechanism necessary for rapid assembly of cytoskeletal filaments and for morphological polarity during cell motility. In Dictyostelium discoideum, increased intracellular pH through undefined transport mechanisms plays a key role in directed cell movement. We report that a developmentally regulated Na-H exchanger in Dictyostelium discoideum (DdNHE1) localizes to the leading edge of polarized cells and is necessary for intracellular pH homeostasis and for efficient chemotaxis. Starved DdNHE1-null cells (Ddnhe1–) differentiate, and in response to the chemoattractant cAMP they retain directional sensing; however, they cannot attain a polarized morphology, but instead extend mislocalized pseudopodia around the cell and exhibit decreased velocity. Consistent with impaired polarity, in response to chemoattractant, Ddnhe1– cells lack a leading edge localization of F-actin and have significantly attenuated de novo F-actin polymerization but increased abundance of membrane-associated phosphatidylinositol 3,4,5-trisphosphate (PI(3,4,5)P3). These findings indicate that during chemotaxis DdNHE1 is necessary for establishing the kinetics of actin polymerization and PI(3,4,5)P3 production and for attaining a polarized phenotype.

Abbreviations used in this paper: CRAC, cytosolic regulator of adenylyl cyclase; PH, pleckstrin homology; pHi, intracellular pH; PI3, phosphatidylinositol 3; PI(3,4,5)P3, phosphatidylinositol 3,4,5-trisphosphate.


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