The Activity of Mblk-1, a Mushroom Body-selective Transcription Factor from the Honeybee, Is Modulated by the Ras/MAPK Pathway

Abstract

We previously identified a gene, termed Mblk-1, that encodes a putative transcription factor with two DNA-binding motifs expressed preferentially in the mushroom body of the honeybee brain, and its preferred binding sequence, termed Mblk-1-binding element (MBE) (Takeuchi, H., Kage, E., Sawata, M., Kamikouchi, A., Ohashi, K., Ohara, M., Fujiyuki, T., Kunieda, T., Sekimizu, K., Natori, S., and Kubo, T. The honeybee Apis mellifera L. is a social insect, and colony members perform various exquisite communications to maintain colony activities. Worker bees inform the other foragers of the direction and distance of a food source using dance language (1, 2), which might require complex processing of sensory information in their brains. Little is known, however, regarding the molecular basis of their highly advanced behavior.Mushroom bodies (MBs) 1 are believed to be involved in sensory integration, learning, and memory in insects (3, 4). The honeybee MBs are well developed when compared with those of other insects. In the honeybee, the ratio of volume of MBs to that of whole brain is ϳ12%, whereas that of Drosophila is ϳ2% (5). Moreover, each MB of the honeybee has two calyces composed of two morphologically distinct types of interneurons, the large-and small-type Kenyon cells (5-7). On the other hand, in Drosophila, there is only one calyx, and the Kenyon cells are morphologically indistinct (8). These observations suggest that MB function is closely associated with the advanced honeybee behaviors.To identify molecules involved in the highly advanced behaviors of the honeybees, we previously used the differential display method to identify a gene, termed Mblk-1, that is expressed preferentially in the large-type Kenyon cells of the honeybee brain (9). Mblk-1 encodes a novel protein consisting of 1598 amino acid residues with significant similarity to a nuclear factor encoded by the Drosophila melanogaster CG18389/E93 gene. The CG18389/E93 gene was identified previously as an ecdysone-inducible gene in the prepupal salivary gland (10) and was reported to encode a nuclear protein that is required for ecdysone-triggered programmed cell death during metamorphosis (11). The expression of CG18389/E93 in the adult and the biochemical characteristics of the protein, however, have not been examined.Two putative DNA-binding motifs, termed RHF (region conserved between honeybee and fruit fly) 1 and RHF2, a nuclear localization signal, and Gln run were conserved between Mblk-1 and Drosophila E93 protein (9). RHF2 has significant sequence homology with proteins encoded by genes from nematoda (a polypeptide predicted by an open reading frame of the Caenorhabditis elegans cosmid T01C1), human (three polypeptides predicted by open reading frames of the chromosome 4 clone RP11-173B23 map 4, chromosome 11 clone RP11-162M10 map 11, and chromosome 10 clone RP11-175019, respectively), mouse (12), and sea urchin (a polypeptide predicted by an open reading frame of the Strongylocentrotus purpuratus EST253 coelomocyte cDNA 5Ј-end), suggestin...

Control of target gene specificity during metamorphosis by the steroid response gene E93

“…First, E93 and Pnt could both bind to the Dll bract enhancer and cooperate to activate transcription. A second possibility is suggested by the finding that activity of Mblk-1 is modulated by phosphorylation by MAPK, a component of the EGFR signaling pathway (44). If E93 were similarly modified, signal integration could be achieved simply by the direct activation of Dll by phosphorylated E93.…”

Classical Olfactory Conditioning in the Cockroach Periplaneta americana

“…One such gene is Mblk-1 , which is expressed preferentially in large Kenyon cells of the MB, encodes a putative transcription factor with two DNA-binding motifs, and might function downstream of the Ras/MAPK pathway (Takeuchi et al ., 2001;Park et al, 2002Park et al, , 2003. Fujiyuki et al .…”

Transcriptional responses in eastern honeybees (Apis cerana) infected with mites, Varroa destructor

“…Mblk-1, a transcription factor involved in the neuronal circuits of mushroom bodies (MBs), is preferentially expressed in the mb of the honeybee brain (Takeuchi et al, 2001;Park et al, 2003). Grooming and hygienic behaviors are social behaviors in honeybees that may require complex processing of sensory information.…”