Tailless patterning functions are conserved in the honeybee even in the absence of Torso signaling

In Drosophila, the maternal Torso terminal signaling pathway activates expression of the gene tailless (tll), which is required for the patterning of anterior and posterior termini. We cloned the honeybee orthologue of tll (Am-tll) and found that embryonic expression of Am-tll resembles that of Drosophila, with expression in triangular anterior dorsal-lateral domains and a posterior cap. Functional studies revealed that Am-tll has an essential role in patterning the posterior terminal segments and the brain, similar to the activity of tll in other insects. As the honeybee genome lacks many of the components of the Torso pathway required for terminal patterning, we investigated the regulation of honeybee tailless (Am-tll). Am-tll is expressed maternally and, in the honeybee ovary, Am-tll mRNA becomes localized to the dorsal side of the oocyte, a process requiring the actin cytoskeleton. This RNA becomes redistributed in early embryos to a posterior domain. We also show that the activation of the anterior domain of Am-tll is dependent on honeybee orthodenticle-1. Together these findings indicate major differences in post-transcriptional regulation of tailless in the honeybee compared to other insects but that this regulation leads to a conserved expression pattern. These results provide an example of an early event in development evolving and yet still producing a conserved output for the rest of development to build upon.