A. Raibaud et al., Cryofracture electron microscopy of the ookinete pellicle of Plasmodium gallinaceum reveals the existence of novel pores in the alveolar membranes, J STRUCT B, 135(1), 2001, pp. 47-57
The malaria parasite invades the midgut tissue of its mosquito host as a mo
tile form called the ookinete. We have examined the pellicle of the ookinet
e of Plasmodium gallinaceum by freeze-fracture and quick-freeze, deep-etch
electron microscopy. The general organization is analogous to that of invas
ive stages of other members of Apicomplexa. The pellicle is composed of thr
ee membranes: the plasma membrane, and the two linked intermediate and inne
r membranes, which in the ookinete form one flattened vacuole that is locat
ed beneath the plasma membrane. The edges of this vacuole form a longitudin
al suture. Beneath the vacuole is found an array of microtubules that are c
onnected to the inner membrane by intramembranous particles. During freeze-
fracture, the membranes can split along their hydrophobic planes, thus yiel
ding six fracture faces, each of which displays a characteristic pattern of
intramembranous particles. Additionally, we find that the ookinete pellicl
e differs from all other apicomplexan motile stages by the presence of larg
e pores. These pores are of unknown function, but clearly might constitute
a novel pathway for the transport of molecules to and from the cortex, whic
h is independent of the well-described route through the apical micronemal/
rhoptry complex. The pores may be the route by which motor proteins or othe
r nonmicronemal surface proteins are trafficked, such as P25/P28 and SOAP,
some of which are implicated in transmission blocking immunity. (C) 2001 Ac
ademic Press.