Juvenile hormone promotes vitellogenin expression in post-embryonic stages of Apis mellifera females

A.R. Barchuk 1, M.M.G. Bitondi 2 & Z.L.P. Simões 2

1 Depto. Genética FMRP-Universidade de São Paulo Av Bandeirantes 3900, 14049-900 Ribeirão Preto, (SP,) Brazil, Universidade de São Paulo

Vitellogenin (Vg) synthesis by the fat body is normally restricted to females and is especially intense in queens (only very little quantities of this protein are detected in drones). The Vg synthesis program of adults queens cannot be modified by juvenile hormone (JH) applications, in contrast to workers, in which low concentrations of JH are permissive to Vg synthesis, but high concentrations are repressive. Little is known on the mechanisms that regulate the initial expression of this protein in Apis mellifera. Our recent studies indicate that Vg synthesis starts during the pupal period, where it initiates distinctly earlier in queens than in workers. In addition, our results suggest that the initiation of Vg expression in Apis mellifera is more related to JH than previously thought. To determine the participation of this hormone in pupal Vg expression, we tested the effects of topical JH applications on different postembryonic stages of Apis mellifera. JH-III (10 ? g in 2 ? l of acetone) was administered to pink- and brown-eyed pupae (controls were treated with the respective solvent). The hemolymph of subsequent stages was collected and analyzed for vitellogenin presence. Western blots of conventional SDS-PAGE were assayed utilizing a rabbit antiserum raised against honeybee egg proteins. Rocket immunoelectrophoresis was employed for the quantitative determination of the Vg fraction in hemolymph. The clearest effect of exogenous JH was the anticipation of Vg expression in both castes. While in control groups Vg appeared only in pupae with a strongly melanized thorax, in JH treated groups it already appeared in pupae with a medium pigmented thorax. The caste-specific regulatory mechanism, however, appears to persist also in the presence of artificially elevated JH titers, since JH advanced Vg expression in queens to slightly earlier stages than in workers. Most importantly, our results suggest that the initiation of Vg synthesis in the pupal stages is governed by other factors than those maintaining Vg synthesis, particularly in adult queens. During the late pupal stages, as well as in the first days after emergence, ecdysteroid titers are relatively low in queens and workers, but differences are observed in the JH titer, which is already higher in queens. It is quite possible that the initiation of Vg synthesis in Apis mellifera could be determined by a combination of these two hormones, resulting in the caste-specific program of Vg synthesis in the adults.

Index terms: honey bee, fat body, pupal development, JH, yolk

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