Molecular characterization and role of ecdysone membrane receptor

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We clarified developmental profiles of gene expression of early response genes to 20E in the anterior silk glands during the fifth instar up to the time of cell death execution two days after gut purge. Also, we showed the gene response to 20E in vitro using anterior silk glands of gut-purged larvae. The in vivo and in vitro results indicated that a heterodimeric EcR-B1 and USP-2 may be responsible for the cell death Results also indicated involvement of E74, E75, BHR3 and BR-C isoforms, but not Ftz-F1. We are not succeeded in gene cloning of the putative membrane ecdysone receptor yet. We examined pharmacologically the signaling pathway from mEcR to cellular responses, i.e. cell condensation, nuclear condensation, DNA fragmentation and nuclear fragmentation. Ca<2+> acts as the second messenger The mEcR is suggested to be a G-protein coupled receptor (GPCR) associated with Gαq, followed by a serial activation of phospholipase c-β, generation of inositol 3-phosphate (IP_3), and release of Ca<2+> from endoplasmic reticulum probably through IP3 receptor Then, Ca<2+> activates protein kinase C (PKC) and caspase 3-like protease. This signaling pathway culminates in nuclear fragmentation and nuclear fragmentation. Nuclear condensation is regulated by a different pathway involving calmodulin and calmodulin-dependent protein kinase II (CaMK-II). However, this pathway was not activated by Ca<2+>, and therefore it is unknown whether Gαq is involved in this pathway. In addition, inhibitors of calmodulin and CaMK-II affected the occurrence of nuclear and DNA fragmentations, indicating the caspase 3-like protease activation does not depend simply on the signaling pathway of GPCR/PLC-β/IP3/Ca<2+>/PKC.