The Origin and Structure of Centrosomes in Embryos derived from Haplodiploid Parthenogenetic Insects

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In most animal cells, the centrosomes, or microtubule organizing centers (MTOC), play akey role in chromosome segregation during nuclear division. They consist of a pair of centriolesencompassed by a complex protein matrix. In most organisms, the centrioles are paternallyderived from the sperm basal body and the surrounding components are primarily derived fromthe maternal cytoplasm. Organisms that undergo parthenogenetic development provide anopportunity to study natural variants in centrosome formation and structure. The insect orderHymenoptera (this includes ants, bees, and wasps) is characterized by haplodiploidparthenogenesis, whereby unfertilized eggs develop as males and fertilized eggs develop asfemales. Although the genetics, behavior, and ecology of species within this order have beenintensively studied, surprisingly few studies have directly focused on issues pertaining to thecentrosome. Preliminary results for one species within this order, the jewel wasp Nasoniavitripennis, demonstrate that centrosomes form despite the lack of a sperm-derived basal body.Numerous cytoplasmic asters form in both fertilized and unfertilized eggs after the completion ofmeiosis. In unfertilized eggs, two of these cytoplasmic asters are captured by the femalepronucleus and these function as the zygotic centrosomes while the unassociated astersdisappear. In fertilized embryos, the sperm derived centrosomes function as the zygoticcentrosomes and the cytoplasmic asters disappear. Because unfertilized eggs develop into malesand fertilized eggs into females, this is the first system described in which centrosomes arereciprocally inherited. This project seeks to further characterize centrosome inheritance andstructure in Nasonia. These studies are likely to yield novel mechanisms of organizingMTOCs and also provide new insights concerning the evolution and developmental consequencesof parthenogenesis. The three specific aims of this project are:1. To further characterize the behavior of the cytoplasmic asters in fertilized and unfertilizedembryos through live fluorescent microscopy.2. To characterize the centrosome inheritance pattern in Nasonia strains in which developmentof unfertilized or fertilized eggs is specifically disrupted.3. To characterize the composition and structure of the asters and centrosomes in fertilized andunfertilized embryos through immunofluorescent analysis and thick section electronmicroscopy.