The Babesia bovis hap2 gene is not required for blood stage replication, but expressed upon in vitro sexual stage induction

Abstract

Babesia bovis, is a tick borne apicomplexan parasite responsible for important cattle losses globally. Babesia parasites have a complex life cycle including asexual replication in the mammalian host and sexual reproduction in the tick vector. Novel control strategies aimed at limiting transmission of the parasite are needed, but transmission blocking vaccine candidates remain undefined. Expression of HAP2 has been recognized as critical for the fertilization of parasites in the Babesia-related Plasmodium, and is a leading candidate for a transmission blocking vaccine against malaria. Hereby we identified the B. bovis hap2 gene and demonstrated that it is widely conserved and differentially transcribed during development within the tick midgut, but not by blood stage parasites. The hap2 gene was disrupted by transfecting B. bovis with a plasmid containing the flanking regions of the hap2 gene and the GPF-BSD gene under the control of the ef-1α-B promoter. Comparison of in vitro growth between a hap2-KO B. bovis clonal line and its parental wild type strain showed that HAP2 is not required for the development of B. bovis in erythrocytes. However, xanthurenic acid-in vitro induction experiments of sexual stages of parasites recovered after tick transmission resulted in surface expression of HAP2 exclusively in sexual stage induced parasites. In addition, hap2-KO parasites were not able to develop such sexual stages as defined both by morphology and by expression of the B. bovis sexual marker genes 6-Cys A and B. Together, the data strongly suggests that tick midgut stage differential expression of hap2 is associated with the development of B. bovis sexual forms. Overall these studies are consistent with a role of HAP2 in tick stages of the parasite and suggest that HAP2 is a potential candidate for a transmission blocking vaccine against bovine babesiosis.

Identification of a putative methyltransferase gene of Babesia bigemina as a novel molecular biomarker uniquely expressed in parasite tick stages

“…As a result, in vivo induction of sexual stages would be expected to occur non-synchronously and the rise and fall of ccp expression would be masked. In addition to ccp2 and ccp3 , expression of hap2 , a gene found to be important in B. bovis sexual stage development [ 16 ], was upregulated at 6 h but, unlike the expression pattern of the ccp genes, remained elevated at 15 and 24 h after TCEP induction (Additional file 2 : Figure S2), consistent with a previous study [ 13 ].…”

Characterization of Cystoisospora suis sexual stages in vitro

“…The results in C. suis correlate with previous reports on Eimeria and Toxoplasma. HAP2 is found in microgametes and unsporulated oocysts but not in sporulated oocysts or sporozoites [26,27,40,48,49]. Moreover, transcription of HAP2 was increased during the enteric development of T. gondii in the intestine of cats.…”

“…budding and faithful segregation of genetic material. A point mutation in a conserved portion of the gene causes a severe mitotic defect [48]. In Plasmodium, Nima1 is found in replicative forms of the parasites, in asexual and sexual stages, with a role in mitosis, and specifically in microgametes.…”

Sequencing-based phylogenetic-study of Babesia spp detected in tick tissues in Al-Diwaniyah province, Iraq

“…Different genera and species of ticks such as Hyalomma and Rhipicephalus are well-known for their enhancement to transmit Babesia species to different animals (4). This microorganism has a lifestyle of asexual proliferation in animal hosts and a sexual-based life-style in ticks (5). A regular, but not too much trustworthy, diagnostic tool is the microscopic diagnosis of Babesia spp that has been used for decades till now to perform the diagnosis of this protozoan.…”