Abstract
Malaria parasite transmission requires differentiation of male and female gametocytes into gametes within a mosquito following a blood meal. A mosquito-derived molecule, xanthurenic acid (XA), can trigger gametogenesis, but the signalling events controlling this process in the human malaria parasite Plasmodium falciparum remain unknown. A role for cGMP was revealed by our observation that zaprinast (an inhibitor of phosphodiesterases that hydrolyse cGMP) stimulates gametogenesis in the absence of XA. Using cGMP-dependent protein kinase (PKG) inhibitors in conjunction with transgenic parasites expressing an inhibitor-insensitive mutant PKG enzyme, we demonstrate that PKG is essential for XA- and zaprinast-induced gametogenesis. Furthermore, we show that intracellular calcium (Ca2+) is required for differentiation and acts downstream of or in parallel with PKG activation. This work defines a key role for PKG in gametogenesis, elucidates the hierarchy of signalling events governing this process in P. falciparum, and demonstrates the feasibility of selective inhibition of a crucial regulator of the malaria parasite life cycle.
Highlights
Plasmodium falciparum is the causative agent of the most lethal form of malaria, thought to kill over a million people each year
By using genetically modified malaria parasites in combination with specific inhibitors of the protein kinase, we have illustrated the feasibility of blocking development of the sexual stage of the parasite’s life cycle
We have used a genetic approach combined with specific inhibitors to show conclusively that in P. falciparum, cGMP-dependent protein kinase (PKG) is essential for mediating initiation of gametogenesis, and we provide evidence that the enzyme may be activated in a narrow temporal window prior to Ca2þ signalling
Summary
Plasmodium falciparum is the causative agent of the most lethal form of malaria, thought to kill over a million people each year. Male gametocytes undergo a series of spectacular changes, including three rounds of genome replication and mitotic division, resulting in the release of eight highly motile, flagellated gametes within only 10 min [6,7]. Observation of this process (known as exflagellation) by Laveran in 1880 was one of the first major clues that malaria was caused by a parasitic protozoan [8].
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