Calcium promotes the hatching process of Chlamydomonas
Stephanie Davis1, Takeaki Kubo2, and Pinfen Yang1
1) Biological Sciences, Marquette University, Milwaukee WI 53233, USA
2) Division of Integrated Life Sciences, Kyoto University, Kyoto 606-8502, Japan
Hatching poses a challenge for the study of Chlamydomonas flagella. After mitosis, daughter cells supposedly generate flagella and then release the flagella-associated sporangin, a calcium-dependent hatching protease that severs mother cell wall. However, many mutants, defective in flagellar movement or length, often remain unhatched despite the presence of calcium. Sometimes, suspension with distilled water or Hepes buffer induces hatching. It will be valuable to reveal the critical factors that stall or induce hatching. We found that unhatched mutant cells have flagella devoid of sporangin, indicating distinct regulation of flagellar elongation and sporangin transport. Hatching rates decrease drastically as liquid cultures approach the stationary phase while calcium supplement alleviates the decline. Reduction of hypotonicity to a critical level triggers hatching of every tested strain at the log phase including flagella-less fla10-2, bld2 and bld10 that is defective in anterograde intraflagellar transport or the basal body. Mother cells usually enlarge and hatch within 10 min, while longer for flagella-less or deprived cells. The threshold varies depending on strains and deprivation. Hatching is promoted by light and KCl that depolarizes cell membrane; tempered by NaCl, EGTA, mastoparan and calcium channel blockers; and independent of protein synthesis. These results strongly suggest that hypotonicity-induced calcium surge bypasses the cell cycle control to trigger the release of sporangin primarily through para-basal body area and flagella.
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