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

University Of California-Santa Cruz, Santa Cruz CA

Investigators

Abstract

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 centrioles encompassed by a complex protein matrix. In most organisms, the centrioles are paternally derived from the sperm basal body and the surrounding components are primarily derived from the maternal cytoplasm. Organisms that undergo parthenogenetic development provide an opportunity to study natural variants in centrosome formation and structure. The insect order Hymenoptera (this includes ants, bees, and wasps) is characterized by haplodiploid parthenogenesis, whereby unfertilized eggs develop as males and fertilized eggs develop as females. Although the genetics, behavior, and ecology of species within this order have been intensively studied, surprisingly few studies have directly focused on issues pertaining to the centrosome. Preliminary results for one species within this order, the jewel wasp Nasonia vitripennis, 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 of meiosis. In unfertilized eggs, two of these cytoplasmic asters are captured by the female pronucleus and these function as the zygotic centrosomes while the unassociated asters disappear. In fertilized embryos, the sperm derived centrosomes function as the zygotic centrosomes and the cytoplasmic asters disappear. Because unfertilized eggs develop into males and fertilized eggs into females, this is the first system described in which centrosomes are reciprocally inherited. This project seeks to further characterize centrosome inheritance and structure in Nasonia. These studies are likely to yield novel mechanisms of organizing MTOCs and also provide new insights concerning the evolution and developmental consequences of parthenogenesis. The three specific aims of this project are: 1. To further characterize the behavior of the cytoplasmic asters in fertilized and unfertilized embryos through live fluorescent microscopy. 2. To characterize the centrosome inheritance pattern in Nasonia strains in which development of unfertilized or fertilized eggs is specifically disrupted. 3. To characterize the composition and structure of the asters and centrosomes in fertilized and unfertilized embryos through immunofluorescent analysis and thick section electron microscopy.