Juvenile hormone analog binding in Manduca epidermis

Of a series of derivatives of JH I and methoprene, iodovinylmethoprenol (IVMA) proved most active ( ed 50 s of 3.2 pmol and 20 nM in the Manduca black larval assay and in the prevention of the 20-hydroxyecdysone-induced change to pupal commitment in the epidermis in vitro , respectively). When incubated with nuclei isolated from day 1 fifth instar abdominal epidermis, [ 125 I]IVMA bound specifically to two components with K d s of 4 and 59 nM. This binding was competed by IVMA and methoprene but not by JH I; similar binding by [ 3 H]JH I was not competed by IVMA or methoprene. Specific binding of IVMA was not found in pupally committed epidermis from wandering larvae, but it reappeared in pupal abdominal and thoracic epidermis but not in the wings. Culture of day 2 fifth instar epidermis with 20-hydroxyecdysone to cause pupal commitment caused the loss of the IVMA nuclear binders whereas culture in the absence of hormortes had no effect, indicating that 20HE in the absence of JH downregulates JH receptors.