Meeting Abstract
The insect segmented body plan is conserved and stereotypical, but the embryonic processes leading to this body plan are variable. In long germ segmentation, best known from Drosophila melanogaster, a hierarchy of gene interactions results in the generation of all segments in the blastoderm. This derived mechanism is found in most holometabolous insects. Short germ (sequential) segmentation involves clock-like oscillations that produce most trunk segments post gastrulation. Sequential segmentation is ancestral, and is the predominant process in hemimetabolous insects. However, the segmentation process in most insects actually uses a mix of both mechanisms. The anterior-most segments are formed in the blastoderm, while the remaining segments appear sequentially from a growth zone, during the germ-band stage. In order to understand how long germ development evolved from the ancestral short germ pattern, we study the hemipteran Oncopeltus fasciatus, a species that displays intermediate germ segmentation, including a blastoderm stage similar to that of Drosophila, and a growth zone with sequential segmentation. We ask whether blastoderm segmentation in Oncopeltus is more similar to the sequential segmentation in its growth zone or to the simultaneous segmentation seen in Drosophila. Analysis of four segmentation genes: engrailed, wingless, even-skipped and delta during blastoderm stages of Oncopeltus show that blastoderm segments appear almost simultaneously. In addition, knocking down gap genes leads to loss of specific segments in the blastoderm. These results point to the fact that blastodermal segmentation in Oncopeltus is similar to the segmentation process in Drosophila, raising the possibility that Drosophila maintains the vestiges of an ancient process originally used only for anterior segments. This provides insights into the evolution of long-germ development.
