The evolution of antero-posterior patterning in the long germ insect embryo

One of the first steps in the development of a single-celled embryo includes the establishment of the anterior-posterior (AP) and dorsal-ventral (DV) axes. Subsequently a complex patterning program ensues along these axes to ultimately give rise to a basic adult body plan. The mechanisms employed by the embryo to achieve this initial polarization have long fascinated developmental biologists and various strategies have now been identified among different animal species for achieving this general polarization of the embryo. Moreover, it is clear that while certain mechanisms and aspects of these signaling networks are conserved throughout the animal kingdom, the patterning network continues to evolve. The early patterning of the fruit fly Drosophila melanogaster is one of the most well described developmental systems, providing an excellent comparison for work on the evolution of the patterning networks among insects. It has become clear that the crux of the Drosophila patterning network, the gene bicoid, as well as the basic mode of development within the fruit fly are not well conserved developmental features among insects. Many researchers have thus sought to identify a more general ancestral patterning network and mode of development within the group of insects. I have used the wasp Nasonia viripennis to identify mechanisms utilized for the initial polarization of the insect embryo and to identify features of the early patterning network. Nasonia provides a powerful model system in which to study the evolution of the patterning network with regard to what is known from Drosophila development. Nasonia, like Drosophila undergoes a long germ mode of development, yet lacks the highly derived anterior patterning gene bicoid. My work has focused on the functional comparison of the well-conserved posterior patterning gene caudal and its place within the genetic patterning network of both Drosophila and Nasonia. Moreover, I have examined the different strategies employed by Nasonia to achieve localization of maternal mRNAs during oogenesis. I have found both microtubule-dependent and -independent mechanisms for the localization of various maternal mRNAs to the different poles of the oocyte. Moreover, I have ascribed novel and conserved roles for the genes Bicaudal-D and tudor in mRNA localization and oocyte specification.