Ca2+ chemotaxis inDictyostelium discoideum

Abstract

SummaryUsing a newly developed microfluidic chamber, we have demonstrated in vitro that Ca 2+ functions as a chemoattractant of aggregationcompetent Dictyostelium discoideum amoebae, that parallel spatial gradients of cAMP and Ca 2+ are more effective than either alone, and that cAMP functions as a stronger chemoattractant than Ca 2+ . Effective Ca 2+ gradients are extremely steep compared with effective cAMP gradients. This presents a paradox because there is no indication to date that steep Ca 2+ gradients are generated in aggregation territories. However, given that Ca 2+ chemotaxis is co-acquired with cAMP chemotaxis during development, we speculate on the role that Ca 2+ chemotaxis might have and the possibility that steep, transient Ca 2+ gradients are generated during natural aggregation in the interstitial regions between cells.

The IplA Ca++ Channel OfDictyostelium discoideumIs Necessary For Ca++, But Not cAMP Chemotaxis, And Plays A Fundamental Role In Natural Aggregation

“…Instead, we found that although iplA -cells undergo a normal chemokinetic surge in velocity in response to the increasing phase of each naturally relayed cAMP wave in wild-type aggregation territories, they lose the ability to reorient towards the aggregation center at the onset of the front of each wave. These results support a hypothesis, previously entertained (Scherer et al, 2010), that transient Ca 2+ gradients might be generated between cells at the onset of the front of each natural relayed cAMP wave that augment orientation towards the center of an aggregation territory, the source of each wave. If this hypothesis proves to be true, it would provide a more complex context for interpreting mutations that affect natural chemotaxis.…”

“…mechanoreception) (Fache et al, 2005;Lombardi et al, 2008). Together, these results suggested that IplA was a strong candidate for a cell surface molecule or a molecule in the signal transduction pathway that mediated the facilitating effects of extracellular Ca 2+ on motility and cAMP chemotaxis, and/or Ca 2+ chemotaxis (Lusche et al, 2009;Scherer et al, 2010). Here, we provide evidence that IplA plays selective roles in the extracellular effects of Ca 2+ on cell behavior.…”

“…To test for Ca 2+ chemotaxis, we designed a microfluidic chamber that generates stable Ca 2+ gradients ( Fig. 2C) (Scherer et al, 2010). Although this chamber can be used to assess chemotaxis in spatial gradients of Ca 2+ or cAMP, it produces strong shear forces, which can effect flow-directed movement (Scherer et al, 2010).…”

“…For that reason, they must be present at optimum concentrations in the natural environment . For the soil amoeba Dictyostelium discoideum to achieve maximum velocity either the extracellular concentration of Ca 2+ must reach 10 mM or the concentration of K + reach 40 mM (Lusche et al, 2009;Lusche et al, 2011;Scherer et al, 2010). Moreover, for D. discoideum amoebae to orient in a spatial gradient of the chemoattractant cAMP, either Ca 2+ must reach 5 mM, or K + or Na + reach 15 mM (Lusche et al, 2009;Lusche et al, 2011).…”

“…In addition to its role in facilitating motility and chemotactic orientation, Ca 2+ also acts as a chemoattractant. When developing cells attain chemotactic responsiveness to spatial gradients of extracellular cAMP, they also attain chemotactic responsiveness to spatial gradients of extracellular Ca 2+ (Scherer et al, 2010). Deletion of the gene for the putative sodium/hydrogen exchanger Nhe1 (NheA) (Patel and Barber, 2005) resulted in the loss of K + as a facilitator of polarity and motility, and the loss of Na + or K + as a facilitator of chemotactic orientation in a spatial gradient of cAMP .…”