The Molecular Mechanism of a Male Killing Gene

Project Summary Sexual reproduction is a battleground for inherited bacteria and their hosts, yet how maternally-inherited bacteria modify the reproductive biology of their host species to favor the fitness of infected females is largely unresolved. Wolbachia are the archetypes of this adaptive strategy and exist globally in nearly half of all arthropod species and many filarial nematodes, making them one of the most widespread microorganisms in the animal world. In a variety of arthropod orders, Wolbachia selectively kill sons of infected females in a process termed male killing. This form of sex-specific lethality enhances the spread of the bacteria by increasing the fitness of transmitting females through reduced competition with their dead brothers for limited resources. It can also spur host adaptive responses including male mate choice to avoid the costs of reproductive parasitism or Wolbachia density suppression as males become rare in populations experiencing high levels of male killing. Notably, population genetic models specify that male killing bacteria can speed up the eradication of target pest populations when used in conjunction with the sterile insect technique. However, despite six decades of research on male killing and its relevance to ecology, evolution, cell biology, and vector control, the mechanistic bases remain enigmatic and one of the field’s most central challenges to resolve. We recently identified a gene, hereafter termed WO Male Killing (wmk) from the prophage WO region of Wolbachia, that can cause male killing. When wmk is transgenically expressed in uninfected D. melanogaster embryos, it kills nearly half of male embryos in association with an increase in Dosage Compensation Complex activity and DNA damage. Additionally, the canonical cytological defects caused by male killing Wolbachia are also enriched in wmk-expressing embryos. This project will test the central hypothesis that the Wmk protein kills males by disrupting host transcription in early embryogenesis via host DNA binding and transcriptional misregulation. In Aim 1, we will assess if Wmk acts as a transcription factor to induce male killing by binding host DNA and altering gene expression. In Aim 2, we will interrogate the regions and conserved sites of the Wmk protein necessary to induce male death and the dependency of male killing on early versus late embryonic expression. In Aim 3, we will test if Wmk transport from the cell is mediated by the type IV secretion system, phage particles, or vesicles. Despite decades of intensive research and applications to pest control studies, the details surrounding the mechanistic basis of male killing remain a central question.