Studies of Wolbachia/host interactions and centrosome formation in insect eggs

Insects are one of the most successful groups of higher organisms in nature. This is owed in large part to their high fecundity, as females generate numerous eggs throughout their lives to insure their reproductive success. Additionally, insects have evolved a number of different genetic mechanisms, such as diploploidy and haplodiploidy, which establish the development of males and females. Both egg production and sex determination in insects rely on the coordination of multiple cytoskeletal events that occur in the developing egg, or oocyte. Recent studies have suggested that these cytoskeletal components may be exploited by the endoparasitic bacteria Wolbachia to insure their successful transmission. Here I present two studies that investigate various aspects of Wolbachia/host interactions at the cellular level as well as insect egg development. First, in a detailed analysis of Wolbachia distribution in the female germline of Drosophila melanogaster, I show that Wolbachia utilize host microtubules and the minus end-directed motor Dynein for localization in the early oocyte. Thus, an association between Wolbachia and these cytoskeletal factors appear to be important for efficient maternal transmission of these bacteria. In a second study, I provide genetic evidence that Wolbachia do not cause cytoplasmic incompatibility by inducing developmental synchrony between paternal and maternal pronuclei during early embryonic development. In a third study, I investigate the cellular origin of maternal centrosomes that form in unfertilized Hymenopteran (haplodiploid) embryos. The origin of these centrosomes has been a longstanding puzzle, since typically the sperm is needed to bring in paternal centrioles to seed centrosome formation in the early embryo. I provide evidence that Hymenopteran centrosomes arise from organelles known as accessory nuclei, which are derived from the nuclear envelope of the germinal vesicle. I provide preliminary evidence that Wolbachia may manipulate the formation of these structures to induce parthenogenesis in some haplodiploid species.