Carbohydrate metabolism genes and pathways in insects: insights from the honey bee genome.

Carbohydrate-metabolizing enzymes may have particularly interesting roles in the honey bee, Apis mellifera, because this social insect has an extremely carbohydrate-rich diet, and nutrition plays important roles in caste determination and socially mediated behavioural plasticity. We annotated a total of 174 genes encoding carbohydrate-metabolizing enzymes and 28 genes encoding lipid-metabolizing enzymes, based on orthology to their counterparts in the fly, Drosophila melanogaster, and the mosquito, Anopheles gambiae. We found that the number of genes for carbohydrate metabolism appears to be more evolutionarily labile than for lipid metabolism. In particular, we identified striking changes in gene number or genomic organization for genes encoding glycolytic enzymes, cellulase, glucose oxidase and glucose dehydrogenases, glucose-methanol-choline (GMC) oxidoreductases, fucosyltransferases, and lysozymes.

Specification of auditory sensitivity by Drosophila TRP channels.

Ears achieve their exquisite sensitivity by means of mechanical feedback: motile mechanosensory cells through their active motion boost the mechanical input from the ear. Examination of the auditory mechanics in Drosophila melanogaster mutants shows that the transient receptor potential (TRP) channel NompC is required to promote this feedback, whereas the TRP vanilloid (TRPV) channels Nan and Iav serve to control the feedback gain. The combined function of these channels specifies the sensitivity of the fly auditory organ.

Identification of a novel gene, Mblk-1, that encodes a putative transcription factor expressed preferentially in the large-type Kenyon cells of the honeybee brain.

Mushroom bodies (MBs) are considered to be involved in higher-order sensory processing in the insect brain. To identify the genes involved in the intrinsic function of the honeybee MBs, we searched for genes preferentially expressed therein, using the differential display method. Here we report a novel gene encoding a putative transcription factor (Mblk-1) expressed preferentially in one of two types of intrinsic MB neurones, the large-type Kenyon cells, which makes Mblk-1 a candidate gene involved in the advanced behaviours of honeybees. A putative DNA binding motif of Mblk-1 had significant sequence homology with those encoded by genes from various animal species, suggesting that the functions of these proteins in neural cells are conserved among the animal kingdom.

Concentrated expression of Ca2+/ calmodulin-dependent protein kinase II and protein kinase C in the mushroom bodies of the brain of the honeybee Apis mellifera L.

We have previously used the differential display method to identify a gene that is expressed preferentially in the mushroom bodies of worker honeybees and to show that it encodes a putative inositol 1,4,5-trisphosphate receptor (IP3R) homologue (Kamikouchi et al. [1998] Biochem. Biophys. Res. Commun. 242:181-186). In the present study, we examined whether the expression of some of the genes for proteins involved in the intracellular Ca2+ signal transduction is also concentrated in the mushroom bodies of the honeybee by isolating cDNA fragments that encode the Ca2+/calmodulin-dependent protein kinase II (CaMKII) and protein kinase C (PKC) homologues of the honeybee. In situ hybridization analysis revealed that the expression of these genes was also concentrated in the mushroom bodies of the honeybee brain: The CaMKII gene was expressed preferentially in the large-type Kenyon cells of the mushroom bodies, whereas that for PKC was expressed in both the large and small types of Kenyon cells. The expression of the genes for IP3R and CaMKII was concentrated in the mushroom bodies of the queen and drone as well as in those of the worker bee. Furthermore, the enzymatic activities of CaMKII and PKC were found to be higher in the mushroom bodies/central bodies than in the optic and antennal lobes of the worker bee brain. These results suggest that the function of the intracellular Ca2+ signal transduction is enhanced in Kenyon cells in comparison to other neuronal cell types in the honeybee brain.

Soldier caste-specific gene expression in the mandibular glands of Hodotermopsis japonica (Isoptera: termopsidae).

Although "polymorphic castes" in social insects are well known as one of the most important phenomena of polyphenism, few studies of caste-specific gene expressions have been performed in social insects. To identify genes specifically expressed in the soldier caste of the Japanese damp-wood termite Hodotermopsis japonica, we employed the differential-display method using oligo(dT) and arbitrary primers, compared mRNA from the heads of mature soldiers and pseudergates (worker caste), and identified a clone (PCR product) 329 bp in length termed SOL1. Northern blot analysis showed that the SOL1 mRNA is about 1.0 kb in length and is expressed specifically in mature soldiers, but not in pseudergates, even in the presoldier induction by juvenile hormone analogue, suggesting that the product is specific for terminally differentiated soldiers. By using the method of 5'- and 3'-rapid amplification of cDNA ends, we isolated the full length of SOL1 cDNA, which contained an ORF with a putative signal peptide at the N terminus. The sequence showed no significant homology with any other known protein sequences. In situ hybridization analysis showed that SOL1 is expressed specifically in the mandibular glands. These results strongly suggest that the SOL1 gene encodes a secretory protein specifically synthesized in the mandibular glands of the soldiers. Histological observations revealed that the gland actually develops during the differentiation into the soldier caste.

Preferential expression of the gene for a putative inositol 1,4,5-trisphosphate receptor homologue in the mushroom bodies of the brain of the worker honeybee Apis mellifera L.

A gene expressed preferentially in the mushroom bodies of the brain of the worker honeybee Apis mellifera L. was identified by the differential display method and its cDNA was isolated. The cDNA fragment of 534 bp (clone A1) contained an open reading frame encoding 177 amino acid residues having 78, 72, 70, 59 and 55% sequence identities with the inositol 1,4,5-trisphosphate (IP3) receptors of Drosophila melanogaster, Xenopus laevis and humans (types 1, 2 and 3), respectively, suggesting that it encodes a putative IP3 receptor homologue of the honeybee. In situ hybridization revealed that the gene encoding clone A1 was expressed preferentially in the mushroom bodies and not in the optic lobes, antennal lobes and central bodies; in the mushroom body, it was expressed strongly in the large type Kenyon cells and weakly in the small type Kenyon cells. Reverse transcription polymerase chain reaction analysis showed that the gene was expressed strongly in the head and weakly in the antennae, legs, thorax, and abdomen. These results suggest that the A1 gene product plays a crucial role in neural transmission in the mushroom bodies of the worker bee brain.