Molecular mechanisms for Wolbachia hub tropism in Drosophila melanogaster. Rama Krishna Simhadri, Michelle Toomey, Parthena Mantis, Ajit Kamath, Horacio Frydman. Biology, Boston University, Boston, MA.

   Wolbachia are symbiotic intracellular bacteria that infect reproductive organs of a wide range of insects and worms, many of which have medical relevance. The bacteria are maternally transmitted analogous to mitochondria and have been shown to confer the host a reproductive advantage and increased resistance to many viruses that cause Dengue, West Nile and Chikungunya, and parasites like Plasmodium. Recently several field trials have been successfully conducted to spread Wolbachia in wild mosquito populations to reduce the spread of these diseases. Understanding the molecular and cellular basis of Wolbachia transmission and increase of insect resistance against human pathogens are highly relevant towards developing these Wolbachia-based approaches for disease control. Working in this direction we have found that Wolbachia displays tissue tropism which is dependent on the strain of Wolbachia. Specifically we are looking at the tropism of two strains of Wolbachia - wMel and wMelPop, which are native to Drosophila melanogaster. The two strains differ considerably in their infection levels in the niche harboring the stem cells in the testis under some conditions. To understand the molecular details of this strain specific phenotype, we have performed transcriptional analysis on the apical tips of the testis containing the niche, associated stem cells and primary spermatocytes. This analysis revealed several genes that are deferentially expressed between the three groups - uninfected, wMel infected and wMelPop infected tissue, and most of them are involved in processes related to Metabolism, including protelolysis, lipid metabolism, transport, oxidation-reduction and cell cycle. In agreement with previous work indicating that Wolbachia depends on host amino acid pool as an energy source, our data indicates greater proteolytic activity in the Wolbachia strain with higher niche tropism - wMelPop. We are currently validating these results and by utilizing the genetic tools available in Drosophila, we will test the functional significance of the candidate genes for tissue tropism.