Malaria parasite development in the mosquito vector
Plasmodium parasites, the unicellular protozoan parasites which cause malaria, have a complicated life cycle within two hosts. Our research focuses on the early event during the transmission from the mammalian host to the mosquito vector. Immediately after uptake of an infected blood meal the sexual stage is initiated. Gametocytes, which are formed in the blood of the mammalian host, mature to gametes within 10 minutes after uptake of the blood. In turn, the gametes fuse to form a zygote, which within the next 24 hours develops into a polar and motile cell, called the ookinete. The ookinete traverses the midgut epithelium, develops into a sporogonic cell called the oocyst. During the next 2 weeks in each oocyst thousands of infectious sporozoites are formed, which then travel to the salivary gland where they are injected when the mosquito takes a new blood meal.
Oocysts (green) developing in the mosquito midgut labeled with an antibody against Anopheles gambiae E-cadherin (red). Parasites and mosquito stained for DNA (blue)
Aim of research
In the laboratory we study gametogenesis and the development from zygotes to ookinetes. These are complex and little known processes, which are unique to this group of organisms. Our work aims at identifying gene products which are essential for these developmental stages. Investigations are hampered by the fact that malaria parasites are evolutionary diverged with a unique life style, evidenced by the fact that ~50% of the annotated proteins have no similarity to known proteins.
Bioinformatics is used to identify genes expressed at each stage and further analysis uses a combination of expression analysis, reverse genetics, and advanced microscopy techniques to elucidate the role of candidates.
A deeper understanding of these processes is a prerequisite for developing novel intervention strategies with the goal of blocking transmission through the mosquito.
Current view of events leading to the formation of male gametes
Exflagellating male (red) among red blood cells (green)
Egress of gametocytes from the host red blood cell
Our laboratory has identified three of the four proteins which are known to have a role in the escape of the gametocytes from the host cell. This is a complex process involving the rupture of two membranes which surround the gametocyte: the parasite derived parasitophorous vacuole membrane and the red blood cell plasma membrane. We have shown that the protein MDV-1/PEG3, and a stage-specific actin, actin2, have important functions in the former process, while a perforin-like protein is the first parasite protein identified being essential for rupture of the red cell membrane.
Superresolution microscopy of a male gametocyte labelled for MDV-1/PEG3 (green) and actin (red)
Mutant male gametocyte lacking actin2 is trapped within the red blood cell. Arrows point to the flagellar male gamete.
The ookinete is a polar and motile cell. The ookinete uses its own motile system to invade and traverse the midgut epithelial cells, employing an unusual kind of gliding motility. We have participated in the elucidation of the mechanism of motility through studies of actin and myosin, and we have showed that motility is regulated by a calcium-dependent protein kinase.
Ookinetes labeled with antibodies against tubulin (green) and actin (red)