Calcium signal regulates temperature-dependent transformation of sporozoites in malaria parasite development.

The infection by the malaria parasite of its mammalian host is initiated by the asexual reproduction of the parasite within the host hepatocyte. Before the reproduction, the elongated sporozoites undergo a depolarizing morphogenesis to the spherical exo-erythrocytic form (EEF). This change can be induced in vitro by shifting the environmental conditions, in the absence of host hepatocytes. Using rodent malaria parasites expressing a FRET-based calcium sensor, YC3.60, we observed that the intracellular calcium increased at the center of the bulbous structure during sporozoite transformation. Modulators of intracellular calcium signaling (A23187 and W-7) accelerated the sporozoite-rounding process. These data suggest that calcium signaling regulates the morphological development of the malaria parasite sporozoite to the EEF, and support a fundamental role for calcium as a universal transducer of external stimuli in the parasitic life cycle.