methoprene and ethoxyprecocene

The hormonal induction of vitellogenesis in insects and in oviparous vertebrates are prime models of gene regulation in eukaryotes. In vertebrates the process is under estrogenic control and normally confined to females, although males can be artificially induced. In locust in contrast, juvenile hormone (JH) is central to fat body development in both males and females, yet the response is strongly sex limited not only for vitellogenin production but also in terms of total protein, DNA and RNA synthesis and nuclear ploidy levels. To differentiate further possible sex and/or JH related developmental aspects in locusts, large-scale nuclear events were examined during normal adult maturation and in animals treated with antiallatropins and JH analogs. Fat body nuclei undergo extensive restructuring during normal development in both sexes. This included progressive nuclear enlargement, accompanied by extensive proliferation of nuclear matrix components and elaboration of complex inclusion bodies (NB). The isolated protein matrix was unusually complex relative to similar structures from vertebrates and the NB were firmly anchored to it. Although matrix proteins were qualitatively similar to those from other sources, as assessed by SDS polyacrylamide gel electrophoresis, several major matrix polypeptides, including lamins A and B, and components greater than 150 kD, fluctuated quantitatively during development and in concert with nuclear enlargement. The number and morphology of the NB were unrelated to sex, but increased in direct proportion to absolute nuclear volumes. All changes were more pronounced in females, where higher ploidy levels, larger nuclei and correspondingly more internal matrix elements occurred. Suppression of JH production by precocene prevented all foregoing nuclear changes, but re-exposure to methoprene rapidly induced normal development. The results are compared to analogous nuclear changes in steroid responsive vertebrate tissues.

Topics: Adipose Tissue; Animals; Benzopyrans; Cell Nucleus; Cytoplasmic Granules; Fat Body; Female; Grasshoppers; Juvenile Hormones; Male; Methoprene; Microscopy, Electron; Sexual Maturation

The lipid-transport lipoprotein, lipophorin (Lp), an abundant plasma protein of insects, is synthesized in the fat body of Locusta migratoria as a polypeptide of relative mass (Mr) = 85 000. No posttranslational modification could be detected. Precipitation of this protein leads to formation of a product of Mr about 240 000, which fails to dissociate under treatment with sodium dodecyl sulfate and beta-mercaptoethanol. In adult female locusts, synthesis and secretion of protein by the fat body increases three- to four-fold from emergence until day 7 of adult life, Lp representing 15-30% of the total. In the subsequent vitellogenic stage (days 7-14 or later), a further impressive increase in protein output up to five times the previtellogenic rate is observed, followed by a decrease to the previtellogenic level at the end of the cycle. This fluctuation is mainly due to production of the yolk precursor protein, vitellogenin (Vg), which makes up some 60% of the secreted protein at the peak of the cycle. Production of Lp does not follow these dramatic changes. Inactivation of the corpora allata, the source of juvenile hormone (JH), by treatment with precocene, prevents the synthesis of Vg in females, and diminishes the production of other proteins, including Lp, in both sexes. Normal secretion patterns can be restored by application of the JH analog, methoprene. It is concluded that, whereas the synthesis of Vg is dependent upon and intensely stimulated by JH, the synthesis of Lp is stimulated only to a minor extent, in common with other proteins.

Topics: Adipose Tissue; Animals; Benzopyrans; Carrier Proteins; Corpora Allata; Fat Body; Female; Grasshoppers; In Vitro Techniques; Juvenile Hormones; Kinetics; Leucine; Lipoproteins; Male; Methoprene; Reproduction; Vitellogenins