Wolbachia spp. are bacterial endosymbionts that infect several arthropod species. The prophage-containing symbiont alters host reproduction, for example, by causing embryonic death when infected males mate with uninfected females or females that lack the same Wolbachia strain, a process known as cytoplasmic incompatibility. Previous studies identified two cytoplasmic incompatibility factor genes, cifA and cifB, which are encoded by prophage WO in the wMel strain of Wolbachia, to be responsible for cytoplasmic incompatibility. CifA and CifB invade the nuclei of developing Drosophila melanogaster spermatids and alter the abundance of histone and protamine nucleoproteins.

Now, Kaur, Bordenstein and colleagues report the mechanism whereby the Cif proteins modulate macromolecules of the developing sperm. They found that CifA is an RNase that depletes a long non-coding RNA that is required for the transformation of histone to protamine during sperm chromatin organization, a process crucial for sperm development. Moreover, they report that CifA and CifB are DNases that cause DNA damage in elongating spermatids and that fertilization by the modified sperm causes embryonic DNA damage and death.