Kinesin-8B controls basal body function and flagellum formation and is key to malaria transmission

Abstract

Eukaryotic flagella are conserved microtubule-based organelles that drive cell motility. Plasmodium, the causative agent of malaria, has a single flagellate stage: the male gamete in the mosquito. Three rounds of endomitotic division in male gametocyte together with an unusual mode of flagellum assembly rapidly produce eight motile gametes. These processes are tightly coordinated, but their regulation is poorly understood. To understand this important developmental stage, we studied the function and location of the microtubule-based motor kinesin-8B, using gene-targeting, electron microscopy, and live cell imaging. Deletion of the kinesin-8B gene showed no effect on mitosis but disrupted 9+2 axoneme assembly and flagellum formation during male gamete development and also completely ablated parasite transmission. Live cell imaging showed that kinesin-8B–GFP did not co-localise with kinetochores in the nucleus but instead revealed a dynamic, cytoplasmic localisation with the basal bodies and the assembling axoneme during flagellum formation. We, thus, uncovered an unexpected role for kinesin-8B in parasite flagellum formation that is vital for the parasite life cycle.

Plasmodium bergheikinesin-5 associates with the spindle apparatus during cell division and is important for efficient production of infectious sporozoites

“…The loss of kinesin-5 may have been compensated for by the over-expression of another member of the kinesin family, therefore we analysed the transcript level of kinesin-8B, kinesin-8X and kinesin-13 in gametocytes of Δ kinesin-5 parasites. These kinesins are highly expressed in gametocytes and have important role during male gametogony [23,30]. We found that the kinesin-13 transcript level was significantly upregulated ( Fig.…”

“…The transgenic parasites also produced gametocytes in mice, and therefore next we analysed male and female gametocyte differentiation following activation in the exflagellation/ookinete medium that mimics the mosquito gut environment. Male and female gametes emerge from the infected erythrocyte, and in the case of male gamete development this is preceded by three rapid rounds of genome duplication, resulting in eight flagellate male gametes [22,23]. There was no defect in male gamete exflagellation for either of the Δ kinesin-5 parasite clones, with the same exflagellation frequency as WT-GFP parasites ( Fig.…”

“…The first type of mitosis occurs during asexual proliferation, with multiple asynchronous nuclear divisions producing up to 32 nuclei (during schizogony in the blood of the vertebrate host) or more than 1000 nuclei (during schizogony in the liver of the vertebrate host and sporogony in the mosquito gut), with cytokinesis occurring only after nuclear division is complete, to produce haploid progeny cells [19][20][21][22]. The second type of mitosis is during male gametogony (part of the sexual stage in the mosquito gut) where there are three rapid rounds of DNA replication from 1N to 8N within 10 to 15 minutes, followed by karyokinesis and cytokinesis to produce 8 flagellate haploid male gametes [22,23]. The first phase of meiotic division occurs following fertilization as the zygote differentiates into a motile ookinete in the mosquito gut.…”

“…As cell division in Plasmodium is atypical, so the molecules regulating cell division are also divergent from those of higher eukaryotes [24][25][26][27]. The large family of kinesins includes molecular motors that are essential for several processes during cell division [28,29], and in Plasmodium berghei there are nine kinesin genes, including two kinesin-8 genes that are important in cell division and male gamete formation [23,30]. There is a single Plasmodium kinesin-5, and since this protein plays an important role during cell proliferation in many eukaryotes, and is considered as a strong target for the development of therapeutics against many diseases including malaria [31], we decided to study its role during cell division in the malaria parasite.…”

A divergent cyclin/cyclin-dependent kinase complex controls the atypical replication of a malaria parasite during gametogony and transmission

“…Current evidence suggests that certain canonical cell-cycle checkpoints are absent 16 . For example, compounds that interfere with mitotic spindle formation do not prevent DNA replication proceeding 17,18 , while spindle formation is not affected in a mutant that is unable to replicate DNA 18,19 . Recently, we observed that proteins involved in DNA replication and cytoskeletal reorganisation are phosphorylated during the first seconds of gametogony 20 .…”