Transition of Plasmodium Sporozoites into Liver Stage-Like Forms Is Regulated by the RNA Binding Protein Pumilio

Abstract

Many eukaryotic developmental and cell fate decisions that are effected post-transcriptionally involve RNA binding proteins as regulators of translation of key mRNAs. In malaria parasites (Plasmodium spp.), the development of round, non-motile and replicating exo-erythrocytic liver stage forms from slender, motile and cell-cycle arrested sporozoites is believed to depend on environmental changes experienced during the transmission of the parasite from the mosquito vector to the vertebrate host. Here we identify a Plasmodium member of the RNA binding protein family PUF as a key regulator of this transformation. In the absence of Pumilio-2 (Puf2) sporozoites initiate EEF development inside mosquito salivary glands independently of the normal transmission-associated environmental cues. Puf2- sporozoites exhibit genome-wide transcriptional changes that result in loss of gliding motility, cell traversal ability and reduction in infectivity, and, moreover, trigger metamorphosis typical of early Plasmodium intra-hepatic development. These data demonstrate that Puf2 is a key player in regulating sporozoite developmental control, and imply that transformation of salivary gland-resident sporozoites into liver stage-like parasites is regulated by a post-transcriptional mechanism.

Translational Control in Plasmodium and Toxoplasma Parasites

“…These untranslated mRNAs are stored for translation after fertilization. RNA-binding proteins (Puf proteins) that repress translation by binding to the mRNA 3= untranslated region are specifically upregulated in gametocytes (Puf1 and Puf2) (27,28) and sporozoites (Puf2) (46,47). The phosphorylation of eIF2␣ in salivary gland sporozoites, mature schizonts, and gametocytes induces translational repression and storage of untranslated mRNAs as stress granules (42,52).…”

“…It has been suggested that the phosphatase in the salivary glands may be repressed by the RNA-binding protein Puf-2. Indeed, when Puf2 is knocked out in P. berghei, the sporozoites start transforming into liver stages while inside the mosquito salivary glands (46,47).…”

Depletion of the Trypanosome Pumilio Domain Protein PUF2 or of Some Other Essential Proteins Causes Transcriptome Changes Related to Coding Region Length

“…Meanwhile, Puf6p is involved in translational repression and localization of the ASH1 mRNA (12). Pumilio domain proteins in malaria parasites effect stage-specific translational repression (13,14). In contrast, some pumilio proteins have also been shown to increase expression: for example, in Caenorhabditis elegans olfactory sensory neurons, Fas-binding factor 1 (FBF-1) promotes translation of egl-4 mRNA by binding to its 3=-UTR (15).…”

The RNA-binding protein PfPuf1 functions in the maintenance of gametocytes in Plasmodium falciparum

“…Intriguingly, in one study, Puf2 knockout in P. berghei altered the gametocyte sex ratio, as observed in P. falciparum (Muller et al, 2011), whereas sex ratio was unchanged with Puf2 knockout in either P. berghei (GomesSantos et al, 2011) or P. yoelii (Lindner et al, 2013). The functions of Puf2 during sporozoite development appear to be conserved in these two rodent parasite species (Gomes-Santos et al, 2011;Lindner et al, 2013). Puf2 deletion in both rodent parasite species resulted in the loss of infectivity and in premature transformation of sporozoites to exoerythrocytic forms, though such changes occurred much earlier during sporogony in P. berghei than in P. yoelii.…”

“…Disruption of PfPuf2 results in increased gametocyte differentiation and elevation of the male-to-female sex ratio (Miao et al, 2013). Studies on the Puf2 protein in P. berghei and P. yoelii have shown that knockout of Puf2 results in failure of maintenance of sporozoites in mosquito salivary glands and premature transformation of sporozoites into liver-stage-like parasites (Gomes-Santos et al, 2011;Lindner et al, 2013;Muller et al, 2011). However, Puf1 knockout in P. berghei did not reveal any noticeable phenotypic changes during parasite development (Gomes-Santos et al, 2011;Muller et al, 2011).…”