Nanos Plays a Conserved Role in Axial Patterning outside of the Diptera

Abstract

Axial patterning is a fundamental event in early development, and molecules involved in determining the body axes provide a coordinate system for subsequent patterning [1, 2]. While orthologs of Drosophila bicoid and nanos play a conserved role in anteroposterior (AP) patterning within at least a subset of Diptera [3–5], conservation of this process has not yet been demonstrated outside of the flies. Indeed, it has been argued that bicoid, an instrumental “anterior” factor in Drosophila melanogaster, acquired this role during the evolution of more-derived dipterans [6, 7]. Interestingly, the interaction of Drosophila maternal nanos and maternal hunchback provides a system for patterning the AP axis that is partially redundant to the anterior system [8–11]. Previous studies in grasshoppers suggest that hunchback may play a conserved role in axial patterning in this insect [12], but this function may be supplied solely by the zygotic component of hunchback expression. Here we provide evidence that the early pattern of zygotic grasshopper Hunchback expression is achieved through translational repression that may be mediated through the action of grasshopper nanos. This is consistent with the notion that an anterior gradient system is not necessary in all insects and that the posterior pole “probably conveys longitudinal polarity on the ensuing germ anlage” [13].