A honey bee Dscam family member, AbsCAM, is a brain-specific cell adhesion molecule with the neurite outgrowth activity which influences neuronal wiring during development.

The immunoglobulin superfamily (IgSF) has been indicated as functioning in the development and maintenance of nervous systems through cell-cell recognition and communication in several model invertebrates, Drosophila melanogaster and Caenorhabditis elegans. To further explore the functions of the IgSF in the brain of an invertebrate with more complex behavior, we identified and characterized a novel brain-specific Dscam family member, AbsCAM, from honey bee (Apis mellifera). The level of the AbsCAM protein was high in newly hatched bees and was dramatically reduced with age. The AbsCAM protein level was constant among worker bees of the same age performing different tasks, suggesting that it was primarily determined by age and not task in adult brains. Two different AbsCAM transcripts (AbsCAM-Ig7A and B) were generated by the alternative splicing of exon 11 encoding immunoglobulin domain 7 in an age-dependent manner. AbsCAM was expressed in the major brain neuropils where the synaptic density was high. AbsCAM can mediate the isoform-specific homophilic cell adhesion in vitro, and affected the axonal projections in Drosophila embryonic central nervous system and adult mushroom body by ectopic expression. Furthermore, AbsCAM promoted the neurite outgrowth of cultured neurons isolated from honey bee pupal brains. These results thus suggest that AbsCAM is the first honey bee IgSF implicated as functioning in neuronal wiring during honey bee brain development.

Effect of in vitro administered 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on DNA-binding activities of nuclear transcription factors in NIH-3T3 mouse fibroblasts.

TCDD is a very toxic environmental contaminant which is known to cause a variety of toxic symptoms in many species. Because of a myriad of biochemical changes TCDD is known to induce in many test animals, it has been difficult to pinpoint the causative event common to all those symptoms in different species. One of the research avenues we have been following is identification of the pattern of TCDD-induced changes in DNA binding characteristics of nuclear transcription factors (NTFs), each of which has the property to trigger a set of coordinated changes in many gene expressions. Since in our previous work we studied animals affected by TCDD in vivo using gel mobility shift assay approached with32P labeled oligonucleotide probes, we examined in the current study the possibility whether we could establish an equivalent in vitro system in NIH-3T3 mouse fibroblast cells so as to be able to learn the similarities and the dissimilarities of TCDD-induced responses of NTFs between in vitro and in vivo. The results indicated that, for a large part, this in vitro test system could reasonably reproduce the pattern of changes occurring in vivo at the early stages of TCDD's action in terms of induced changes in binding of thes NTSs to DNA. The key features were TCDD induced upregulation of NTFs binding to the response elements for AP-1, dioxin (DRE) and T3 (thyroid hormone) and down-regulation of those to response elements (REs) for c-Myc, Sp-1 and retinoic acid receptor (RARE). However, the time course required the changes in DNA binding activity was much shorter in vitro. To study the basic cause for such changes in NTF binding, we studied the effects of exogenously added EGF, forskolin, TPA (12-0-tetradecanoylphorbol acetate) and TNFalpha on the expression of TCDD's action on some of these NTFs. The results showed that these agents indeed greatly influence the outcome. The most influential agents were TNFalpha, forskolin and EGF. These results indicate that this in vitro cell model is useful in simulating the action of TCDD with respect to its basic action on NTFs.

Conservation of novel Mahya genes shows the existence of neural functions common between Hymenoptera and Deuterostome.

Honeybees have been shown to exhibit cognitive performances that were thought to be specific to some vertebrates. However, the molecular and cellular mechanisms of such cognitive abilities of the bees have not been understood. We have identified a novel gene, Mahya, expressed in the brain of the honeybee, Apis mellifera, and other Hymenoptera. Mahya orthologues are present in Deuterostomes but are absent or highly diverged in nematodes and, intriguingly, in two dipteran insects (fruit fly and mosquito) and Lepidoptera (silk moth). Mahya genes encode novel secretory proteins with a follistatin-like domain (Kazal-type serine/threonine protease inhibitor domain and EF-hand calcium-binding domain), two immunoglobulin domains, and a C-terminal novel domain. Honeybee Mahya is expressed in the mushroom bodies and antennal lobes of the brain. Zebra fish Mahya orthologues are expressed in the olfactory bulb, telencephalon, habenula, optic tectum, and cerebellum of the brain. Mouse Mahya orthologues are expressed in the olfactory bulb, hippocampus, and cerebellum of the brain. These results suggest that Mahya may be involved in learning and memory and in processing of sensory information in Hymenoptera and vertebrates. Furthermore, the limited existence of Mahya in the genomes of Hymenoptera and Deuterostomes supports the hypothesis that the genes typically represented by Mahya were lost or highly diverged during the evolution of the central nervous system of specific Bilaterian branches under the specific selection and subsequent adaptation associated with different ecologies and life histories.

Characterization of the two distinct subtypes of metabotropic glutamate receptors from honeybee, Apis mellifera.

L-Glutamate is a major neurotransmitter at the excitatory synapses in the vertebrate brain. It is also the excitatory neurotransmitter at neuromuscular junctions in insects, however its functions in their brains remain to be established. We identified and characterized two different subtypes (AmGluRA and AmGluRB) of metabotropic glutamate receptors (mGluRs) from an eusocial insect, honeybee. Both AmGluRA and AmGluRB form homodimers independently on disulfide bonds, and bind [3H]glutamate with K(D) values of 156.7 and 80.7 nM, respectively. AmGluRB is specifically expressed in the brain, while AmGluRA is expressed in the brain and other body parts, suggesting that AmGluRA is also present at the neuromuscular junctions. Both mGluRs are expressed in the mushroom bodies and the brain regions of honeybees, where motor neurons are clustered. Their expression in the brain apparently overlaps, suggesting that they may interact with each other to modulate the glutamatergic neurotransmission.

The changes of gene expression in honeybee (Apis mellifera) brains associated with ages.

Honeybee (Apis mellifera) worker bees (workers) are known to perform wide variety of tasks depending on their ages. The worker's brains also show the activity and behavior-dependent chemical and structural plasticity. To test if there are any changes of gene expression associated with different ages in the worker brains, we compared the gene expression patterns between the brains of newly emerged bees and old foraging workers (foragers) by macroarray analysis. The expression of genes encoding signal transduction pathway components, ion channels, and neurotransmitter transporters is elevated in the old forager brains, suggesting that the neuronal activities would be enhanced. The mRNA levels of cell adhesion protein, transcription related factors, and plasma membrane associated proteins are also increased in the old forager brains. Meanwhile, the mRNA level of one putative cell adhesion protein is decreased in the old forager brains. These results thus suggest that the dramatic changes of gene expression occur in honeybee brains associated with ages.

The expression of genes encoding visual components is regulated by a circadian clock, light environment and age in the honeybee (Apis mellifera).

The honeybee, Apis mellifera, has been used as a model to study the development of the visual system and adult bee behaviour. However, the regulation of the levels of visual component genes has never been addressed in this organism. We isolated honeybee cDNAs encoding green-sensitive opsin and visual arrestin and then measured their mRNA levels in honeybee workers. Both mRNAs fluctuate on a daily cycle that depends on a pacemaker that functions separately from the pacemaker which controls rhythmic locomotor activity. The cycling-patterns of opsin and arrestin mRNAs are different from each other and are modified by light. Furthermore, light exposure can increase the absolute levels of both mRNAs and the arrestin mRNA level is also dependent on age. Consistent with these results, both mRNA levels are higher in foragers than in in-hive bees under natural conditions. This study thus shows that the expression of genes encoding visual components is regulated by multiple factors and is adjusted to the honeybees' need for vision during the day, and throughout their lives. Comparison of data obtained with honeybees and other organisms indicates that there is a link between the regulation of phototransduction components and vision-related animal behaviour.