Gene expression in the honeybee mushroom body and its gene orthologues

The honeybee Apis mellifera L. is a eusocial insect, and colony members perform various complex communications and divisions of labor to maintain colony activities. Mushroom bodies (MBs) are insect brain structures that are important for higher-order sensory processing of different sensory modalities. Honeybee MB function is thought to be closely associated with honeybee social behavior for the following reasons: (1) The MBs of the aculeate Hymenoptera, including the honeybee, are more prominent compared with those of other insects. (2) Honeybee MBs have a high degree of structural plasticity and the volume of the neuropil varies according to the division of labor. Recently, genes expressed preferentially in the MBs of the honeybee brain were identified using molecular biologic techniques (e.g., differential display method, cDNA microarray, and matrix-assisted laser desorption/ionization with time-of-flight mass spectometry). These genes were classified into three groups according to the function of the proteins encoded: Ca²⁺-signaling pathway, ecdysteroid-regulated transcription factors, and neuropeptide precursor protein. In this article, the expression pattern and possible function of these genes in honeybee MBs is described in comparison with those of their orthologues in other insects.