|1.Research Institution||Nagoya University|
|2.Research Area||Life Sciences|
|3.Research Field||Mechanisms of the Advanced Function in Insects and Proposal of New Insectech|
|4.Term of Project||FY 1999 - FY 2003|
|6.Title of Project||Molecular Mechanisms of Individual Preservation in Insects|
|Name||Institution,Department||Title of Position|
|Toshinobu ,Yaginuma||Nagoya University, Graduate School of Bioagricultural Sciences||Professor|
9.Summary of Research Results
In Bombyx mori, embryonic diapause is induced by an action of a diapause hormone (DH, 24-amino-acids with amidation at the C-terminal) on developing pupal ovaries. For DH activity, the minimum structure is PRL-a. DH is biosynthesized only in 7-paired cells within subesophageal ganglion. By developing a gene transfer system using a recombinant baculovirus, a 30-bp sequence at about -1 k of the DH gene is shown essential to drive the cell-specific expression. A possible factor bound to this cis-element is now proposed. As for DH reception, we identified a G-protein-coupled receptor with 7-transmembrane-domains for DH, which is localized on Bombyx oolemma. In functional analysis using Xenopus oocyte, DH receptor has higher affinity against DH than other FXPRLa peptides. To understand diapause initiation mechanism, we isolated a novel gene (Bm05) expressed abundantly in diapause eggs. When Bm05 was over-expressed in Drosophila by Gal/UAS system, the lifespan of adult flies was prolonged, although the function is yet unclear in Bombyx eggs. To further understand molecular processes of diapause termination promoted by 5°C, we focus on expression mechanisms of the cold-inducible genes such as sorbitol dehydrogenase and Samui (a protein with BAG domain similar to silencer of death domains).
In Antheraea yamamai, diapause occurs at pharate larva and is controlled by two novel peptides, a repressive factor (RF, a pentapeptide) and a maturation factor. Its diapause is broken artificially by imidazole compounds. To understand this artificial termination, an imidazole-compound-binding protein was isolated from diapausing insects. Interestingly, an injection of C16-derivative RF could make Bombyx non-diapause type pupae produce diapause eggs, although a pathway for the mode of action is unclear.
In Gastrophysa atrocyanea, diapausing adults burrow into the soil for 10 months. A diapause-specific peptide (Diapausin) occurs at a higher concentration and acts as a Ca2+ channel blocker. During early diapause (aestivation), a 27-kDa heat-shock protein appears, while during pre- and post-diapause, a novel cellulase-like protein is identified. The RNAi induced diapause-like insects.
Although diapause features in organisms are surely diversified, we believe that common regulatory molecules exist in the level of stopping cell cycles, arresting development and reducing metabolic rates. For example, over-expression of Bm05 expands the lifespan of adult flies. We have generated a transgenic silkworm with the Diapausin gene in order to investigate whether the gene is involved in silkworm longevity. These trials offer attractive potential for Insect Technology (Insectech) in the new century.