The occurrence of a juvenile hormone binding protein and in vitro synthesis of juvenile hormone by the serosa of Locusta migratoria embryos.

At the end of blastokinesis, serosal epitheliae of 4- to 5-day-old embryos of Locusta migratoria contain an immunohistologically detectable cytosolic protein (Mr ∼240 kDa) which is related to the juvenile hormone carrier-protein in the haemolymph of the same species and which binds tritiated juvenile hormone 3 (JH3) (Kd∼10-8 M). At this early stage of development the corpora allata of the embryo are not yet fully differentiated and do not synthesize JH3 in organ cultures. The earliest detectable JH3 production by corpora allata in isolated heads is on day 6. On the other hand, serosal epitheliae of 4- to 5-day-old embryos produce JH3 in organ cultures, as has been shown by methylation of (10-3H)-JH3-acid to (10-3H)-JH3, and by incorporation of tritiated CH3 from L-(methyl-3H)-methionine into JH3. Isolated heads and abdomens of the embryos used as donors for the serosal preparations did not show methyl transferase activity responsible for JH3 biosynthesis. The serosal cells represent a hitherto unrecognized source of methyl transferase activity and of JH3 production. Degradation of JH3 to JH3-acid was also observed.