Gametogenesis, the formation of gametes from gametocytes, an essential step for malaria parasite transmission, is targeted by transmission‐blocking drugs and vaccines. We identified a conserved protein (PBANKA_0305900) in Plasmodium berghei, which encodes a protein of 22 kDa (thus named Pb22) and is expressed in both asexual stages and gametocytes. Its homologues are present in all Plasmodium species and its closely related, Hepatocystis, but not in other apicomplexans. Pb22 protein was localised in the cytosols of schizonts, as well as male and female gametocytes. During gamete‐to‐ookinete development, Pb22 became localised on the plasma membranes of gametes and ookinetes. Compared to the wild‐type (WT) parasites, P. berghei with pb22 knockout (KO) showed a significant reduction in exflagellation (~89%) of male gametocytes and ookinete number (~97%) during in vitro ookinete culture. Mosquito feeding assays showed that ookinete and oocyst formation of the pb22‐KO line in mosquito midguts was almost completely abolished. These defects were rescued in parasites where pb22 was restored. Cross‐fertilisation experiments with parasite lines defective in either male or female gametes confirmed that the defects in the pb22‐KO line were restricted to the male gametes, whereas female gametes in the pb22‐KO line were fertile at the WT level. Detailed analysis of male gametogenesis showed that 30% of the male gametocytes in the pb22‐KO line failed to assemble the axonemes, whereas ~48.9% of the male gametocytes formed flagella but failed to egress from the host erythrocyte. To explore its transmission‐blocking potential, recombinant Pb22 (rPb22) was expressed and used to immunise mice. in vitro assays showed that the rPb22‐antisera significantly inhibited exflagellation by ~64.8% and ookinete formation by ~93.4%. Mosquitoes after feeding on rPb22‐immunised mice also showed significant decreases in infection prevalence (83.3–93.3%) and oocyst density (93.5–99.6%). Further studies of the Pb22 orthologues in human malaria parasites are warranted.

中文翻译：

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一种保守的疟原虫抗原 Pb22 在伯氏疟原虫的雄性配子发生中起关键作用

配子发生是由配子体形成配子，是疟疾寄生虫传播的重要步骤，是传播阻断药物和疫苗的目标。我们在伯氏疟原虫中鉴定出一种保守蛋白 (PBANKA_0305900) ，它编码一种 22 kDa 的蛋白（因此命名为Pb22），并在无性阶段和配子体中均有表达。它的同源物存在于所有疟原虫物种及其密切相关的肝囊虫属中，但不存在于其他顶复门。Pb22 蛋白定位于裂殖体以及雄性和雌性配子体的胞质溶胶中。在配子到合子发育过程中，Pb22 定位在配子和合子的质膜上。与野生型（WT）寄生虫相比，具有pb22敲除 (KO) 的P. berghei在体外合子培养过程中显示雄性配子体的鞭毛 (~89%) 和合子数量 (~97%) 显着减少。蚊子摄食试验表明，蚊子中肠中pb22- KO 系的动子和卵囊形成几乎完全消除。这些缺陷在pb22被恢复的寄生虫中得到了拯救。雄性或雌性配子中有缺陷的寄生虫系的交叉受精实验证实pb22- KO 系中的缺陷仅限于雄性配子，而pb22中的雌性配子‐KO 系在 WT 水平上是肥沃的。对雄性配子发生的详细分析表明，pb22- KO 系中 30% 的雄性配子体未能组装轴丝，而约 48.9% 的雄性配子体形成鞭毛但未能从宿主红细胞中排出。为了探索其传输阻断潜力，重组 Pb22 (rPb22) 被表达并用于免疫小鼠。体外试验表明，rPb22 抗血清显着抑制了约 64.8% 的鞭毛和约 93.4% 的合子形成。以 rPb22 免疫小鼠为食后的蚊子也显示出感染率 (83.3-93.3%) 和卵囊密度 (93.5-99.6%) 的显着降低。有必要进一步研究人类疟疾寄生虫中的 Pb22 直系同源物。