Production of lipophorin in the fat body of adult Locusta migratoria: comparison with vitellogenin

Abstract

The lipid-transport lipoprotein, lipophorin (Lp), an abundant plasma protein of insects, is synthesized in the fat body of L. 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 .apprx. 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 3- to 4-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 5 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 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. The synthesis of Vg is dependent upon and intensely stimulated by JH, and the synthesis of Lp is stimulated only to a minor extent, in common with other proteins.