Plasticity in mRNA expression and localization of orthodenticle within higher Diptera

orthodenticle (otd) genes are found throughout the animal kingdom and encode well-studied homeodomain transcription factors that share conserved functions in cephalization, head segmentation, brain patterning, and the differentiation of photoreceptors. Otd proteins have been proposed as ancestral key players in anterior determination despite a high level of variation in gene expression at early developmental stages: otd is expressed strictly zygotically in the dipteran Drosophila melanogaster, while otd1 mRNA is contributed maternally to the embryo in the coleopteran Tribolium castaneum and maternal otd1 mRNA is localized to the anterior and posterior pole of the oocyte in the hymopteran Nasonia vitripennis. Here we demonstrate that such changes in otd mRNA expression and localization do not need to represent large phylogenetic distances but can occur even within closely related taxa. We show maternal otd expression in the medfly Ceratitis capitata and maternally localized otd mRNA in the caribfly Anastrepha suspensa, two cyclorrhaphan species closely related to Drosophila. This indicates considerable plasticity in expression and mRNA localization of key developmental genes even within short evolutionary distances.