A Putative Plasmodium RNA-Binding Protein Plays a Critical Role in Female Gamete Fertility and Parasite Transmission to the Mosquito Vector

Abstract

Plasmodium falciparum sexual stage gametocytes are critical for parasite transmission from the human host to the mosquito vector. Mature gametocytes generate fertile male (micro-) or female (macro-) gametes upon activation inside the mosquito midgut. While a number of parasite genes have been described that are critical for P. falciparum gametogenesis and fertility, no parasite gene has been shown to have a unique function in macrogametes. The genome of P. falciparum encodes numerous RNA-binding proteins. We identified a novel protein containing a putative RNA-binding domain, which we named Macrogamete-Contributed Factor Essential for Transmission (MaCFET). This protein is expressed in the asexual and sexual stages. Parasites that carry a deletion of MaCFET (Pfmacfet¯), developed normally as asexual stages, indicating that its function is not essential for the asexual proliferation of the parasite in vitro. Furthermore, Pfmacfet¯ male and female gametocytes developed normally and underwent activation to form microgametes and macrogametes. However, by utilizing genetic crosses, we demonstrate that Pfmacfet¯ parasites suffer a complete female-specific defect in successful fertilization. Therefore, PfMaCFET is a critical female-contributed factor for parasite transmission to the mosquito. Based on its putative RNA-binding properties, PfMaCFET might be in involved in the regulation of mRNAs that encode female-specific functions for fertilization or female-contributed factors needed post fertilization.

Pf ARID Regulates P. falciparum Malaria Parasite Male Gametogenesis and Female Fertility and Is Critical for Parasite Transmission to the Mosquito Vector

“…In contrast, we observed no discernible defect in Pfarid – macrogamete formation. The Pfarid – genetic crosses we performed with transgenic lines producing either fertile microgametes ( 6 ) or macrogametes ( 35 ) confirmed a completely penetrant male defect but, surprisingly, also showed that Pf ARID is required for fertility of female gametes. A recent study describing screening for fertility-related genes in the rodent malaria parasite P. berghei , showed that the P. berghei ARID ( Pb ARID) ortholog named MD4 (PBANKA_0102400) is involved in fertility of male gametes only ( 42 ).…”

“…To further substantiate the finding that the lack of ARID causes a male-specific defect, we assessed the fertility of male and female Pfarid – gametes using genetic crosses with gene deletion parasite lines which either formed only fertile female gametes ( Pfcdpk4 – ) ( 6 ) or only fertile male gametes ( Pfmacfet – ) ( 35 ). WT Pf NF54, Pfarid – , Pfcdpk4 – , and Pfmacfet – gametocytes were generated in vitro followed by pairwise mixing and fed to female Anopheles stephensi mosquitoes on day 15 of culture.…”

Malaria parasites utilize two essential plasma membrane fusogens for gamete fertilization

“…4 A). We next examined a sex-specific function for Pf HAP2 and Pf HAP2p using genetic crosses with Pfhap2¯ and Pfhap2p¯ parasites in combination with transgenic parasite lines which formed either fertile female gametes only ( Pfcdpk4¯ ) [ 26 ] or fertile male gametes only ( Pfmacfet¯ ) [ 27 ]. WT Pf NF54, Pfhap2¯ , Pfhap2p¯ , Pfcdpk4¯ , Pfmacfet¯ gametocytes were generated in vitro and cultures were first individually fed to A. stephensi mosquitoes on day 15 of in vitro culture.…”

Pf SRPK1 Regulates Asexual Blood Stage Schizogony and Is Essential for Male Gamete Formation

“…After determining the role of Pf SRPK1 in male gamete formation, we further analyzed the fertility of male and female Pfsrpk1 − gametes. Since gametocytes in Plasmodium occur together and it is not possible to separate them, we performed genetic crosses between Pfsrpk1 − parasites and transgenic parasite lines, which either formed fertile female gametes only ( Pfcdpk4 − ) ( 8 ) or fertile male gametes only ( Pfmacfet − ) ( 41 ). WT Pf NF54, Pfsrpk1 − , Pfcdpk4 − , and Pfmacfet − gametocytes were generated in in vitro culture for 15 days, and cultures were first fed individually to female A. stephensi mosquitoes.…”

“…Furthermore, we showed that Pfsrpk1 − parasites did not transmit to the mosquito vector. Utilizing genetic crosses with transgenic parasite lines producing either fertile female ( 8 ) or male gametes( 41 ), we showed that Pf SRPK1 has mainly a male gender function. Female Pfsrpk1 − gametes were fertile, but our observation that their transmission in the cross with the female-deficient line was reduced might indicate some function in females.…”