Yuichi Iino et al. (2003) International Worm Meeting "Interneuron-selective transcription factor MBR-1 is involved in olfactory plasticity"

Yu Hayashi, Takao Inoue, Takeo Kubo, Takaaki Hirotsu, Hideaki Takeuchi, Hiroyuki Arai, Hirofumi Kunitomo, Masayuki Yamamoto, Yoshihisa Mita, Yuichi Iino

[International Worm Meeting, 2003]

Processing of sensory information is mediated by specialized interneurons in various sensory systems. In insects, interneurons in the mushroom body of the brain (MB interneurons) are important for sensory integration and olfactory learning. We have previously identified the Mblk-1 gene, which encodes a novel transcription factor that is expressed preferentially in the MB interneurons of the honeybee brain.Homology searches revealed that the DNA binding motifs of Mblk-1 have significant sequence similarities with those encoded by a set of genes from nematode, fruit fly, mouse and human. However, the function of these proteins in the nervous system remains unclear. To clarify the role of Mblk-1 homologues, we performed a reverse genetic analysis using C. elegans. We identified a gene, termed mbr-1 (Mblk-1 related factor-1), which carries two DNA binding motifs with significant homologies with those of Mblk-1. mbr-1 promoter::GFP is expressed selectively in restricted sets of head interneurons identified as AIM, RIC, etc. GFP expression is first observed around the 3-fold stage and continues throughout the larval and adult stages, suggesting the possibility that mbr-1 plays a role in differentiation and/or maintenance of the function of these neurons.To investigate mbr-1 functions in sensory processing, an mbr-1 deletion mutant was isolated by the UV/TMP method and tested in chemotaxis and olfactory adaptation assays. Wild-type worms show reduced chemotaxis towards attractive odorants (benzaldehyde, isoamylalcohol and pyrazine) after pre-exposure to the same odorants for 5 min (Hirotsu and Iino, 2002 West Coast Worm Meeting). In contrast, the mbr-1 mutant worms showed a defect in the adaptation to benzaldehyde, while they showed normal plasticity with isoamylalcohol and pyrazine. The defect was rescued by a wild-type mbr-1 transgene, indicating that mbr-1 is involved in adaptation to benzaldehyde. These findings suggest that the transcription factor MBR-1 acts in specific interneuron(s) for olfactory adaptation. We are attempting cell type-specific rescues to identify the interneuron(s) where mbr-1 functions.