Permissive and instructive anterior patterning rely on mRNA localization in the wasp embryo

The long-germ mode of embryogenesis, in which segments arise simultaneously along the anterior-posterior axis, has evolved several times in different lineages of the holometabolous, or fully metamorphosing, insects. Drosophila's long-germ fate map is established largely by the activity of the dipteran-specific Bicoid (Bed) morphogen gradient which operates both instructively and permissively to accomplish anterior patterning. By contrast, all nondipteran long-germ insects must achieve anterior patterning independently of bed. We show that bed's permissive function is mimicked in the wasp by a maternal repression system in which anterior localization of the wasp ortholog of giant represses anterior expression of the trunk gap genes so that head and thorax can properly form.