Kenji Hara, Life Science, Tokyo Gakugei University, 4-1-1 Nukui-kitamachi, Koganei-shi, Tokyo 184-8501, Japan
Mushroom bodies (MBs) are insect brain centers involved in learning and other complex behaviors. In social Hymenoptera, the MBs are large and comprise larger number of Kenyon cells than in solitary insects, and have repeatedly been implied to underlie the social behaviors. We described the MB neurogenesis in the carpenter ant, Camponotus japonicus (Ishii et al., 2005). In the carpenter ant, similarly to the honey bee, all Kenyon cells are produced in a proliferation cluster formed by symmetrical division of MB neuroblast during postembryonic development. Although mature MBs of carpenter ants and honey bees reportedly comprise almost the same number of Kenyon cells, the carpenter ants have approximately half as many MB neuroblasts than are found in the honey bee. Therefore, interspecific comparison of MB neurogenesis across social insects, and also between social and solitary insects will help to better understand the evolution of social behavior. Ecdysone drives the remodeling of the larval nervous system for adult function in insects. Although the MBs are among the targets of ecdysone, little is known about the molecular aspects of MB neurogenesis in social insects. To advance the understanding of neuronal remodeling in social brain, the cDNAs encoding two presumed ecdysone receptor isoforms (CjEcR-A and CjEcR-a) were isolated from the prepupal brains of C. japonicus and characterized. They have common DNA and ligand binding domains linked to distinct amino termini. The ligand response profile of CjEcR was analyzed with GAL4 fusion of the ligand binding domain, and demonstrates that CjEcR genes encode a functional ecdysone receptor. The immunolocalization with antibody against the common region to the isoforms indicates that CjEcR(s) is nuclear, as expected, and found in the MB neuroblasts and Kenyon cells.
Ishii Y., Kubota K. and Hara K. 2005. Zool. Sci. 22: 743-753
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