Characterization of the Morphology, Composition, and Activity of the Germ Plasm in Nasonia vitripennis

The specification of germ cell fate in the wasp Nasonia vitripennis relies on a maternally provided ribonucleoprotein (RNP) complex called the oosome. The oosome is an exceptionally large germ plasm complex that exhibits surprisingly dynamic behavior throughout the pre-blastoderm stage. In this thesis, I provide the first detailed characterization of the oosome, including descriptions of the oosome’s dynamic morphology, the internal organization of mRNAs and membrane-bound organelles, and initial evidence for posttranscriptional activity within the oosome. Using a combination of super-resolution fluorescence microscopy and transmission electron microscopy, I identified lipid droplets and ribosome-associated vesicles widely distributed throughout the oosome interior, where mitochondria are notably absent. I also identified two patterns of mRNA distribution throughout the oosome as either distinct puncta or in a mesh-like network, which correspond to their level of enrichment within the oosome. Surprisingly, all of those tested only weakly co-localize with conserved germline-associated proteins. Three-dimensional reconstructions of oosomes at specific pre-blastoderm stage syncytial nuclear cycles suggest they exhibit the liquid/elastic solid-like behaviors of deformation, fragmentation, relaxation, and membrane wetting. Using a fluorescence assay to detect ribosome association and by measuring mean mRNA intensity, I also provide initial evidence for the occurrence of both degradation and translation within the oosome. How the biophysical properties and composition of the oosome relate to its function in germline development will be an active area of study for which this work provides essential context.