Abstract:
The life cycle of the malaria parasite Plasmodium falciparum is tightly regulated, oscillating between
stages of intense proliferation and quiescence. Cyclic 48-hour asexual replication of Plasmodium is
markedly different from cell division in higher eukaryotes, and mechanistically poorly understood.
Here, we report tight synchronisation of malaria parasites during the early phases of the cell cycle by
exposure to DL-α-difluoromethylornithine (DFMO), which results in the depletion of polyamines. This
induces an inescapable cell cycle arrest in G1 (~15 hours post-invasion) by blocking G1/S transition. Cell
cycle-arrested parasites enter a quiescent G0-like state but, upon addition of exogenous polyamines,
re-initiate their cell cycle. This ability to halt malaria parasites at a specific point in their cell cycle, and to
subsequently trigger re-entry into the cell cycle, provides a valuable framework to investigate cell cycle
regulation in these parasites. We subsequently used gene expression analyses to show that re-entry
into the cell cycle involves expression of Ca2+-sensitive (cdpk4 and pk2) and mitotic kinases (nima and
ark2), with deregulation of the pre-replicative complex associated with expression of pk2. Changes in
gene expression could be driven through transcription factors MYB1 and two ApiAP2 family members.
This new approach to parasite synchronisation therefore expands our currently limited toolkit to
investigate cell cycle regulation in malaria parasites.
