The role of ecdysteroid 22-kinase in the accumulation of ecdysteroids in ovary of silkworm Bombyx mori.

In the silkworm Bombyx mori, ecdysteroid 22-kinase (EcKinase) has been shown to catalyze the conversion of free ecdysteroids to physiologically inactive ecdysteroid 22-phosphates. First, a phylogenetic analysis of EcKinase showed that many proteins homologous to B. mori EcKinase are found mainly in Ecdysozoa, including insects and nematodes. Next, by RT-PCR analysis combined with laser microdissection and by immunohistochemistry, we demonstrated that free ecdysteroids in the B. mori ovary are synthesized in follicle cells and transferred into the oocyte where they are phosphorylated by EcKinase whose mRNA originates from nurse cells and the oocyte itself.