A major role for zygotichunchbackin patterning theNasoniaembryo

Regulation and function of tailless in the long germ wasp Nasonia vitripennis

In the long germ insect Drosophila, the gene tailless acts to pattern the terminal regions of the embryo. Loss of function of this gene results in the deletion of the anterior and posterior terminal structures and the eighth abdominal segment. Drosophila tailless is activated by the maternal terminal system through Torso signaling at both poles of the embryo, with additional activation by Bicoid at the anterior. Here, we describe the expression and function of tailless in a long germ Hymenoptera, the wasp Nasonia vitripennis. Despite the morphological similarities in the mode of development of these two insects, we find major differences in the regulation and function of tailless between Nasonia and Drosophila. In contrast to the fly, Nasonia tll appears to rely on otd for its activation at both poles. In addition, the anterior domain of Nasonia tll appears to have little or no segmental patterning function, while the posterior tll domain has a much more extensive patterning role than its Drosophila counterpart.

Localized maternal orthodenticle patterns anterior and posterior in the long germ wasp Nasonia

The Bicoid (Bcd) gradient in Drosophila has long been a model for the action of a morphogen in establishing embryonic polarity. However, it is now clear that bcd is a unique feature of higher Diptera. An evolutionarily ancient gene, orthodenticle (otd), has a bcd-like role in the beetle Tribolium. Unlike the Bcd gradient, which arises by diffusion of protein from an anteriorly localized messenger RNA, the Tribolium Otd gradient forms by translational repression of otd mRNA by a posteriorly localized factor. These differences in gradient formation are correlated with differences in modes of embryonic patterning. Drosophila uses long germ embryogenesis, where the embryo derives from the entire anterior-posterior axis, and all segments are patterned at the blastoderm stage, before gastrulation. In contrast, Tribolium undergoes short germ embryogenesis: the embryo arises from cells in the posterior of the egg, and only anterior segments are patterned at the blastoderm stage, with the remaining segments arising after gastrulation from a growth zone. Here we describe the role of otd in the long germband embryo of the wasp Nasonia vitripennis. We show that Nasonia otd maternal mRNA is localized at both poles of the embryo, and resulting protein gradients pattern both poles. Thus, localized Nasonia otd has two major roles that allow long germ development. It activates anterior targets at the anterior of the egg in a manner reminiscent of the Bcd gradient, and it is required for pre-gastrulation expression of posterior gap genes.

Wasps, beetles and the beginning of the ends

Recent papers investigating the genes regulating early embryogenesis in the wasp Nasonia vitripennis and the beetle Tribolium castaneum have provided us with important clues as to how early development is controlled in insects other than higher dipterans such as Drosophila melanogaster. The results of these studies demonstrate that in insects that do not have bicoid, anterior patterning is regulated by a combination of maternal orthodenticle and hunchback. Furthermore, during the evolution of long-germ-band development, Nasonia and Drosophila may have evolved different mechanisms to pattern posterior segments, marginalising the important role of the terminal system in short-germ-band embryos.