Apoptosis ofAscogregarina taiwanensis(Apicomplexa: Lecudinidae) which failed to migrate within its natural host

Abstract

SummarySexual reproduction of Ascogregarina taiwanensis (Apicomplexa: Lecudinidae), a parasite specific to the mosquito Aedes albopictus, in malpighian tubules is initiated by the entry of the trophotozoites developed in the midgut shortly afterpupation (usually < 5 h). However, only a low proportion of trophozoites are able to migrate; others end up dying. In this study, we demonstrated those trophozoites which failed to migrate eventually died of apoptosis. Morphological changes such as shrinkage, chromatin aggregations, and formation of blunt ridges on the surface were seen in moribund trophozoites. In addition, DNA fragmentation of trophozoites isolated from the midgut of pupae was demonstrated by the presence of DNA ladders, Annexin V staining, and TUNEL assays. Due to detection of caspase-like activity, apoptosis of those trophozoites may have occurred through a mechanism of an intrinsic or mitochondrial-mediated pathway. Although apoptosis has been observed in various species of protozoa, it is not clear how apoptosis in single-celled organisms might result from evolution by natural selection. However, we speculate that apoptosis may regulate the parasite load of A. taiwanensis within its natural mosquito host, leading to an optimized state of the survival rate for both parasite and host.