FoxP expression identifies a Kenyon cell subtype in the honeybee mushroom bodies linking them to fruit fly αβc neurons

The arthropod mushroom bodies (MB) are a higher order sensory integration centre. In insects, they play a central role in associative olfactory learning and memory. In Drosophila melanogaster (Dm), the highly ordered connectivity of heterogeneous MB neuron populations has been mapped using sophisticated molecular genetic and anatomical techniques. The MB-core subpopulation was recently shown to express the transcription factor FoxP with relevance for decision-making. Here, we report the development and adult distribution of a FoxP-expressing neuron population in the MB of honeybees (Apis mellifera, Am) using in situ hybridisation and a custom-made antiserum. We found the same expression pattern in adult bumblebees (Bombus terrestris, Bt). We also designed a new Dm transgenic line that reports FoxP transcriptional activity in the MB-core region, clarifying previously conflicting data of two other reporter lines. Considering developmental, anatomical and molecular similarities, our data are consistent with the concept of deep homology of FoxP expression in neuron populations coding reinforcement-based learning and habit formation.