The role of calcium in the Chlamydomonas reinhardtii mating reaction.
The mating reaction of Chlamydomonas reinhardtii entails a rapid series of cell-cell interactions leading to cell fusion. We have demonstrated (Pasquale, S. M., and U. Goodenough. 1987. J. Cell Biol. 105:2279-2293) that cAMP plays a key role in this process: gametic flagellar adhesion elicits a sharp increase in intracellular cAMP, and presentation of dibutyryl-cAMP to unmated gametes elicits all known mating responses. The present study evaluates the role of Ca2+ in this system. We document that the mating-induced increase in cAMP, and hence the mating responses themselves, are blocked by a variety of drugs known to interfere with Ca(2+)-sensitive processes. These data suggest that Ca(2+)-mediated events may couple adhesion to the generation of cAMP. Such events, however, appear to be localized to the flagellar membrane; we find no evidence for the mating-related increase in cytosolic free Ca2+ that has been postulated by others. Indeed, by monitoring the length of the Ca(2+)-sensitive centrin-containing nucleus-basal body connector, we show that cytosolic free Ca2+ levels, if anything, decrease in response to cAMP signaling. We confirm a previous report that Ca2+ levels increase in the mating medium, but document that this represents a response to augmented cAMP levels and not a prelude. Finally, we show that IP3 levels remain constant throughout the mating reaction. These results are discussed in terms of the various signal transduction systems that have now been identified in Chlamydomonas.
Goodenough
U W
UW
Department of Biology, Washington University, St. Louis, Missouri 63130.
Shames
B
B
Small
L
L
Saito
T
T
Crain
R C
RC
Sanders
M A
MA
Salisbury
J L
JL
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002450:Cell Communication; D002459:Cell Fusion; D016825:Chlamydomonas reinhardtii / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism*; D010716:Phosphatidylinositols / Q000378:metabolism; D015398:Signal Transduction
D010716:Phosphatidylinositols; D000242:Cyclic AMP; D002118:Calcium