Calmodulin regulates a TRP channel (ADF1) and phospholipase C (PLC) to mediate elevation of cytosolic calcium during acidic stress that induces deflagellation inChlamydomonas

What is it about?

Cilia and eukaryotic flagella (exchangeable terms) are organelles that function in cell motility and signaling. Ciliary defects are associated with a cohort of human diseases and developmental disorders. Calcium has been implicated in several aspects of ciliary biology such as flagellar motility, assembly and disassembly of flagella, and deflagellation. How calcium mediates downstream signaling in these cellular processes is not well understood. Calmodulin (CaM) is a critical calcium transducer and is known to be required for flagellar motility. Whether and how CaM functions in other aspects of ciliary biology is not clear. We have studied CaM in Chlamydomonas, a model organism widely used for flagellar studies. We have found that CaM is enriched in the transition zone and the nucleus basal body connector (NBBC). By analyzing a cam mutant, we have found that loss of CaM shortens the NBBC, impairs flagellar motility and assembly but not flagellar disassembly. Moreover, the cam mutants are defective in pH shock induced deflagellation. Deflagellation requires elevation of cytosolic calcium followed by severing of the axonemal microtubules. We have found that CaM is not involved in microtubule severing but cytosolic rise of calcium. CaM mediates pH-shock induced calcium entry through a TRP channel ADF1 as well as calcium release by indirectly activation of phospholipase C. Thus, this work has provided molecular insights into the function of CaM in ciliary biology. The mechanism of CaM in controlling calcium homeostasis discovered here also has implications in calcium signaling during acidic stress in plant and mammalian cells.

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