The Endosymbiotic Bacterium Wolbachia Selectively Kills Male Hosts by Targeting the Masculinizing Gene

Abstract

Pathogens are known to manipulate the reproduction and development of their hosts for their own benefit. Wolbachia is an endosymbiotic bacterium that infects a wide range of insect species. Wolbachia is known as an example of a parasite that manipulates the sex of its host's progeny. Infection of Ostrinia moths by Wolbachia causes the production of all-female progeny, however, the mechanism of how Wolbachia accomplishes this male-specific killing is unknown. Here we show for the first time that Wolbachia targets the host masculinizing gene of Ostrinia to accomplish male-killing. We found that Wolbachia-infected O. furnacalis embryos do not express the male-specific splice variant of doublesex, a gene which acts at the downstream end of the sex differentiation cascade, throughout embryonic development. Transcriptome analysis revealed that Wolbachia infection markedly reduces the mRNA level of Masc, a gene that encodes a protein required for both masculinization and dosage compensation in the silkworm Bombyx mori. Detailed bioinformatic analysis also elucidated that dosage compensation of Z-linked genes fails in Wolbachia-infected O. furnacalis embryos, a phenomenon that is extremely similar to that observed in Masc mRNA-depleted male embryos of B. mori. Finally, injection of in vitro transcribed Masc cRNA into Wolbachia-infected embryos rescued male progeny. Our results show that Wolbachia-induced male-killing is caused by a failure of dosage compensation via repression of the host masculinizing gene. Our study also shows a novel strategy by which a pathogen hijacks the host sex determination cascade.

Genetic conflicts: the usual suspects and beyond

“…Indeed, many restriction factors that were originally discovered because of their activity against viruses (including retroviruses) were subsequently shown to be potent restrictors of retrotransposons (transposable elements that mobilize via an RNA intermediate and reverse transcriptase activity) (Goodier et al, 2015;Hu et al, 2015;McLaughlin et al, 2014;Moldovan and Moran, 2015;Muckenfuss et al, 2006). However, one mechanism that is unique to transposon control stems from the fact that the transposons are resident within host genomes (among eukaryotic viruses, only retroviruses have this obligate requirement of host genome integration).…”

“…As a result, males represent an 'evolutionary dead-end' for any cytoplasmically inherited bacteria, and they adopt a number of insidious strategies to avoid this fate (B-E). (B) Because male fitness is inconsequential (and may even be harmful) to Wolbachia, it can eliminate male larvae via lethal interaction between the male genotype and the cytoplasmically inherited Wolbachia (Fukui et al, 2015;Hurst and Jiggins, 2000). This maximizes resources available to the female larvae, which can transmit Wolbachia to future generations.…”

Two Conserved Cysteine Residues Are Required for the Masculinizing Activity of the Silkworm Masc Protein

“…Masc encodes a CCCH tandem zinc finger (ZF) protein, which is conserved among lepidopteran insects (6,13,14). Transfection of a B. mori ovary-derived cell line, BmN-4, with Masc cDNA produced the male-type splice variants of Bmdsx (6), as well as enhanced the expression of BmIMP (B. mori IGF-II mRNA-binding protein) (13,14), the product of which is involved in the male-specific splicing of Bmdsx (15).…”

“…Transfection of a B. mori ovary-derived cell line, BmN-4, with Masc cDNA produced the male-type splice variants of Bmdsx (6), as well as enhanced the expression of BmIMP (B. mori IGF-II mRNA-binding protein) (13,14), the product of which is involved in the male-specific splicing of Bmdsx (15). These results indicate that the masculinizing activity of the Masc protein can be assessed in BmN-4 cells by transfecting Masc cDNA derivatives.…”

“…These results indicate that the masculinizing activity of the Masc protein can be assessed in BmN-4 cells by transfecting Masc cDNA derivatives. Using this heterologous assay system, we recently detected the masculinizing activity of the Masc proteins from other lepidopteran insects, that is, Trilocha varians and Ostrinia furnacalis (13,14). However, the domains and/or amino acid residues of the Masc protein that are required for the masculinizing activity are unknown.…”