AUTHOR=Kuniyori Maki , Sato Nariko , Yokoyama Naoaki , Kawazu Shin-ichiro , Xuan Xuenan , Suzuki Hiroshi , Fujisaki Kozo , Umemiya-Shirafuji Rika 

TITLE=Vitellogenin-2 Accumulation in the Fat Body and Hemolymph of Babesia-Infected Haemaphysalis longicornis Ticks

JOURNAL=Frontiers in Cellular and Infection Microbiology

VOLUME=12

YEAR=2022

URL=https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2022.908142

DOI=10.3389/fcimb.2022.908142

ISSN=2235-2988

ABSTRACT=<p>The protozoan parasite <italic>Babesia</italic> spp. invades into tick oocytes and remains in the offspring. The transovarial transmission phenomenon of <italic>Babesia</italic> in ticks has been demonstrated experimentally, but the molecular mechanisms remain unclear. <italic>Babesia</italic> invasion into oocytes occurs along with the progression of oogenesis. In the present study, to find the key tick factor(s) for <italic>Babesia</italic> transmission, we focused on molecules involved in yolk protein precursor (vitellogenin, Vg) synthesis and Vg uptake, which are crucial events in tick oogenesis. With a <italic>Haemaphysalis longicornis</italic> tick–<italic>Babesia ovata</italic> experimental model, the expression profiles of <italic>Akt</italic>, <italic>target of rapamycin</italic>, <italic>S6K</italic>, <italic>GATA</italic>, and <italic>Vg</italic>, Vg synthesis-related genes, and Vg receptor (<italic>VgR</italic>) and autophagy-related gene 6 (<italic>ATG6</italic>), Vg uptake-related genes, were analyzed using real-time PCR using tissues collected during the preovipositional period in <italic>Babesia</italic>-infected ticks. The expression levels of <italic>H. longicornis Vg-2</italic> (<italic>HlVg-2</italic>) and <italic>HlVg-3</italic> decreased in the fat body of <italic>Babesia</italic>-infected ticks 1 day after engorgement. In the ovary, <italic>HlVg-2</italic> mRNA expression was significantly higher in <italic>Babesia</italic>-infected ticks than in uninfected ticks 1 and 2 days after engorgement and decreased 3 days after engorgement. <italic>HlVgR</italic> expression was significantly lower in <italic>Babesia</italic>-infected ticks than in uninfected ticks 2 and 4 days after engorgement. <italic>HlATG6</italic> had a lower gene expression in <italic>Babesia</italic>-infected ticks compared to uninfected ticks 2 days after engorgement. Additionally, western blot analysis using protein extracts from each collected tissue revealed that <italic>H. longicornis</italic> Vg-2 (HlVg-2) accumulate in the fat body and hemolymph of <italic>Babesia</italic>-infected ticks. These results suggest that Vg uptake from the hemolymph to the ovary was suppressed in the presence of <italic>B. ovata</italic>. Moreover, <italic>HlVg-2</italic> knockdown ticks had a lower detection rate of <italic>B. ovata</italic> DNA in the ovary and a significant reduction of <italic>B. ovata</italic> DNA in the hemolymph compared with control ticks. Taken together, our results suggest that accumulated HlVg-2 is associated with <italic>Babesia</italic> infection or transmission in the tick body. These findings, besides previous reports on VgR, provide important information to elucidate the transovarial transmission mechanisms of pathogens in tick vectors.</p>