Polar cell fate stimulates Wolbachia intracellular growth

Abstract

Bacteria are critical partners in the development and evolution of vertebrates and invertebrates. A large fraction of insects harbor Wolbachia, a bacterial endosymbiont that manipulate host reproduction to favor their spreading. Since they are maternally inherited, Wolbachia are under selective pressure to reach the female germline and infect the offspring. However, Wolbachia infection is not limited to the germline. Somatic cell types, including stem cell niches, have higher Wolbachia loads compared to the surrounding tissue. Here we show a novel Wolbachia tropism to the polar cells (PC), specialized somatic cells in the Drosophila ovary. During oogenesis, all stages of PC development are easily visualized, facilitating the investigation of the kinetics of Wolbachia intracellular growth. Wolbachia accumulation is triggered by particular events of PC morphogenesis, including differentiation from progenitors and between stages 8 and 9 of oogenesis. Moreover, induction of ectopic PC fate is sufficient to promote Wolbachia accumulation. We found Wolbachia PC tropism is evolutionarily conserved across most Drosophila species but not in Culex mosquitos. These findings highlight the coordination of endosymbiont tropism with host development and cell differentiation.