Juvenile hormone-dependent LHPI and RNA synthesis in Melanoplus sanguinipes long hyaline tubule: events associated with the "insensitive period".

Juvenile hormone (JH) regulation of the synthesis of LHPI, the major secretory protein of the long hyaline tubule in the male accessory reproductive gland (MARG) of Melanoplus sanguinipes, was examined by in vitro radiolabeling and immunoprecipitation. In MARG taken from normal insects JH III immediately stimulates production of immunospecific LHPI. In contrast, JH III does not initially promote synthesis of LHPI in MARG of allatectomized insects. Only after prior exposure to the hormone [for 24 hr when applied in vivo (topically) or 16 hr under in vitro conditions] is LHPI synthesis enhanced by JH III in the MARG of allatectomized insects. These results suggest that in the prolonged absence of JH III the MARG are "switched off," that is, lose their sensitivity to the hormone. Sensitivity is regained during the 24- or 16-hr "lag phase." Use of the translational inhibitor cycloheximide confirmed the existence of the lag phase in JH III-mediated LHPI synthesis. JH III stimulates RNA synthesis in a dose-dependent manner in the long hyaline tubule at concentrations < 64 nM. Above this level, RNA synthesis was depressed. Actinomycin D given simultaneously with JH III inhibited RNA synthesis, but not the synthesis of LHPI in the long hyaline tubule. It is suggested that understanding the nature of the lag phase will facilitate clarification of the mechanism of action of JH in the MARG.