Plasmodium berghei Brca2 Is Required for Normal Development and Differentiation in Mice and Mosquitoes

Abstract

Background: Malaria is a major global parasitic infestation caused by Plasmodium spp. Its zygotes undergo meiosis and develop into haploid ookinetes which differentiate into oocysts that undergo sporogony. Homologous recombination (HR) occurs during meiosis and introduces genetic variation. However, the mechanisms of HR in Plasmodium are unclear. In humans, the recombinases Rad51 and Dmc1 are required for HR and are regulated by BRCA2. Most eukaryotes harbor BRCA2 homologs. Nevertheless, they have not been reported for Plasmodium.Methods: A Brca2 candidate was salvaged from a database to identify Brca2 homologs in Plasmodium. To confirm that the candidate protein was Brca2, interaction activity between Plasmodium berghei (Pb) Brca2 and Rad51 was tested by a mammalian two-hybrid assay. To elucidate the functions of PbBrca2, it was knocked out and parasite proliferation and differentiation were assessed in mice and mosquitoes. Transmission electron microscopy was used to identify sporogony.Results: The candidate protein was conserved among Plasmodium species and indicated that they harbored critical BRCA2 domains including BRC repeats, tower, and oligonucleotide/oligosaccharide-binding-fold domains. The P. berghei BRC repeats interacted with PbRad51. Hence, this candidate was considered a Brca2 homolog. PbBrca2 knockout parasites were associated with reduced parasitemia, gametocytemia, female gametocyte ratio, oocyst number, and ookinete development in both mice and mosquitoes. Nevertheless, gametocyte and ookinete morphology was comparable with that of wild type parasites. Transmission electron microscopy disclosed that sporogony never progressed in Brca2-knockout parasites.Conclusions: Brca2 is implicated in nearly all Plasmodium life cycle stages and especially in sporogony. PbBrca2 contributes to homologous recombination during meiosis.