20-OH-Ecdysone-induced morphogenetic movements in a Chironomus cell line are accompanied by expression of an embryonic muscarinic system.

The permanent epithelial insect cell line used was derived from Chironomus tentans embryos. Cells are maintained in suspension culture, where they grow as single-layered vesicles. On treatment with the moulting hormone 20-OH-ecdysone cell division ceases. Patches of cuboidal epithelium appear in the vesicles which finally become multilayered and form bud-like protrusions at the outside. In the present study, we localized cholinesterase activity in the cell protrusions by histochemistry and demonstrated coexpression of cholinergic muscarinic receptors by immunofluorescence. Muscarinic receptors were visualized with the monoclonal antibody M35. Six hours after treatment with 20-OH-ecdysone, muscarinic receptors appeared in a few individual cells of the epithelial vesicles before morphological changes became visible. After 24 h, immunofluorescence was concentrated in multilayered patches which now also showed cholinesterase activity. After 3 days, muscarinic receptors and cholinesterase activity were localized in the epithelium protrusions. The results are discussed in the context of an embryonic cholinergic muscarinic system the expression of which has been described in vertebrate and non-vertebrate embryos and is correlated with phases of morphogenesis.