Research

The honeybee (Apis mellifera L. ) is a social insect and the female adults differentiate into two castes: queens and workers. The workers change their roles from nursing the brood, guarding the colony from natural enemies to foraging for nectar and pollen, depending on their age after eclosion (age-polyethism). Furthermore, the workers inform the other foragers of the direction and distance of a food source using dance language. The molecular basis of such highly advanced behaviors of the honeybees, however, remains unclear. The mushroom bodies (MBs) are thought to be important regions for sensory integration, learning, and memory in the insect brain and are well-developed in the honeybee brain. In our laboratory, aiming at identifying candidate genes involved in the highly advanced honeybee behaviors, we have been performing systematic identification of genes expressed in the honeybee brains in MB-preferential and/or behavior-dependent manners using a combination of the differential display method and cDNA microarray analysis. To date, we have reported that the expression of the genes for proteins involved in the Ca²⁺-signaling pathway is upregulated in the MBs in the honeybee brain. We also identified a novel transcription factor, termed Mblk-1, which is expressed selectively in one of the two neural subtypes that comprise the honeybee MBs: a novel non-coding nuclear RNA, termed Ks-1, and a tachykinin-related neurosecretory peptide and a novel non-coding nuclear RNA, termed AncR-1whose expression in the brain differs in association with honeybee behavior. Recently, we identified a novel picorna-like virus, termed kakugo, which is detected selectively in the brains of the aggressive worker bees. Furthermore, we have developed a method to transfer genes into adult honeybee brains by electroporation to facilitate functional analysis of the genes involved in honeybee behaviors. Study on the genes involved in honeybee behavior will contribute to a better understanding of the molecular basis of animal behaviors in general as well as the evolution of insect sociality. A part of this research has been performed in collaboration with the Graduate School of Medicine, University of Tokyo; Faculty of Agriculture, Tamagawa University; Suntory Bioorganic Research Institute; and DNA Chip Research Inc.

Our results suggest that the expression of genes for proteins involved in advanced neural functions is concentrated in the MBs in the honeybee brain. Therefore, a larger-scale screening of genes expressed preferentially in the honeybee MBs might result in further identification of novel genes involved in advanced neural function in general. We are now performing functional analysis of the C. elegans homologue of honeybee Mblk-1 as well as novel genes identified through the screening process described above. The functional analysis of honeybee-derived genes in model animals will contribute to the better understanding of the molecular basis of the neural functions conserved among animal species. A part of this research has been performed in collaboration with the Molecular Genetic Research Laboratory, University of Tokyo; Department of Biophysics and Biochemistry, Graduate School of Science, University of Tokyo; and Graduate School of Pharmaceutical Sciences, University of Tokyo.

There are dozens of specialized huge cells, termed bacteriocytes, in the fat body of the aphid. Bacteriocytes possess a large number of prokaryotic symbionts, termed Buchnera, in their cytoplasm. Recent completion of the whole genome project of Buchnera revealed that the mutual interaction between Buchnera and host bacteriocytes is defined at the genome level. Based on these results, we are now performing functional analysis of Buchnera genes, aiming at identifying key molecules involved in intracellular symbiosis. We have also started proteome analysis, aiming at systematic identification of proteins imported from the cytoplasm of bacteriocytes to Buchnera. We determined that the Buchnera stress protein, termed symbionin, which is expressed predominantly in Buchnera cells, has multiple functions as a molecular chaperon, ptotease, histidine protein kinase, and a phosphotransferase. We are now planning to examine whether symbionin is involved in the signal transduction system in the intracellular symbiosis as a sensor molecule of the two component pathway. We are also looking for the substrate proteins for the molecular chaperon and protease functions of symbionin.

Although regenerative ability is scarce in mammalian organs, some animals possess high ability to regenerate their lost organs. In our laboratory, we identified genes and proteins involved in leg regeneration using the American cockroach (Periplaneta americana). In particular, we have reported that some members of the humoral lectin family (a class of insect defense proteins), termed the Periplaneta lectin family, appear transiently in the regenerating cockroach legs, suggesting common molecular aspects between innate immunity and organ regeneration in insects. We are now working to identify genes involved in tail regeneration in the Xenopus laevis tadpole and their functional analysis using two approaches: The first is the identification of the Xenopus counterparts of the cockroach proteins involved in leg regeneration; the second is the systematic screening of the genes expressed preferentially in the regenerating Xenopus tadpole tails. One of the advantages of using Xenopus laevis as an experimental animal for the study of organ regeneration is that reverse-genetic methods can be applied in this animal. Our goal is to stimulate the regenerative ability in mammals by activating expression of the counterparts of the genes identified as those involved in organ regeneration in Xenopus laevis.