Wolbachia cifBinduces cytoplasmic incompatibility in the malaria mosquito

Abstract

Wolbachia infections are a fascinating example of reproductive parasitism with strong potential to combat vector-borne diseases, due to their combined ability to spread in insect populations and block pathogen replication. Though the Wolbachia factors mediating the notable reproductive manipulation cytoplasmic incompatibility (CI) have now been identified as prophage WO genes cifA and cifB, the relative role of these genes is still intensely debated, with different models claiming that CI requires either both factors or cifB alone. Here we investigated whether cifA and cifB are sufficient to induce conditional sterility in the major malaria vector Anopheles gambiae, a species that appears to have limited susceptibility to invasion by Wolbachia. We report that CI can be fully recapitulated in these mosquitoes, and that cifB is sufficient to cause this reproductive manipulation. cifB-induced sterility is fully rescued by high levels of cifA expression in females. Surprisingly, however, when cifA is highly expressed in males alongside cifB, the CI phenotype is attenuated. cifB strongly impairs fertility also when expressed in the female germline, again mitigated by cifA. These data support a system whereby cifB and cifA must be fine-tuned to exercise CI and rescue, respectively, possibly explaining the limited success of Wolbachia at invading Anopheles. Our findings pave the way towards facilitating Wolbachia infections in anopheline vectors, for use in malaria control strategies.

The Cif proteins from Wolbachia prophage WO modify sperm genome integrity to establish cytoplasmic incompatibility

“…At the genetic level, dual expression of cifA and cifB or single expression of cifB can recapitulate CI; and cifA rescues CI [13,[15][16][17][18][19]52]. However, the cellular and mechanistic bases of CI and rescue remain unresolved and the subject of several questions: When and where do the Cif proteins localize in testes to potentiate CI?…”

The Cif proteins from Wolbachia prophage WO modify sperm genome integrity to establish cytoplasmic incompatibility

“…We previously demonstrated that dual, transgenic expression of cifA and cifB from w Mel Wolbachia in Drosophila melanogaster males induces CI, while single expression of cifA in females rescues CI [ 16 , 17 ]. These results form the basis of the Two-by-One genetic model of CI for several, but not all, strains of Wolbachia [ 13 , 15 , 18 , 19 ]. At the cellular level, CI-defining lethality associates with chromatin defects and mitotic arrest within the first few hours of embryonic development.…”

Nuclease proteins CifA and CifB promote spermatid DNA damage associated with symbiont-induced cytoplasmic incompatibility

“…Notably, the QxxxY motif is also present in T4 CifB of w Pip characterized as a DNase, present in T3 CifB of w No (Adams et al, 2021; Sun et al, 2021) and missing in T1 CifB of w Pip previously deemed to lack nuclease function (Chen et al, 2019). Thus, it is tentatively possible that the QxxxY motif may assist CifB DNase activity since it is localized in CTND, and the sites in CTND are proposed to be involved in substrate binding or catalytic regulation (Xiao et al, 2021).…”

“…Thus, CI is governed by the Two-by-One genetic model demonstrated in various systems (Beckmann et al, 2019; Chen et al, 2019; LePage et al, 2017; Shropshire et al, 2021b; Shropshire and Bordenstein, 2019). cifB alone can also cause cifA -rescuable CI under a One-by-One genetic model (Adams et al, 2021; Sun et al, 2021). Therefore, deciphering the Cif molecular mechanism(s) and potentially universal features of CI and rescue remains a central goal for understanding how sexual reproduction serves as a battleground for host- Wolbachia interactions.…”