Vitellogenesis in the gypsy moth,Lymantria dispar(L.): Characterization of hemolymph vitellogenin, ovarian weight, follicle growth and vitellin content

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Abstract
Gypsy moth vitellin (Vt, greater than 500, 000 daltons) was partially purified from pupal ovarian follicles by high-salt extraction and analyzed by non-SDS- and SDS-PAGE. A large-molecular-weight, female-specific, pupal hemolymph protein (vitellogenin, Vg) had electrophoretic and immuno-staining properties similar to Vt. A slightly larger female-specific hemolymph protein larval-Vt) was found in last-instar female gypsy moth larvae. Vt, pupal-Vg and larval-Vg were recognized on Western blots by a rabbit polyclonal antiserum made against L. dispar Vt. The apoprotein subunits of Vt were 180,000 (apo-Vt180), 165,000 (apo-Vt165), and 38,000 daltons (apo-Vt38). Apo-Vg of similar sizes as the apo-Vt (apo-Vg180, apo-Vg165, and apo-Vg38) were recognized in larval and pupal hemolymph by the anti-Vt antisera. Apo-Vg began to accumulate in the hemolymph of last-instar larvae after day 2 and were not detected by Coomassie-or immuno-staining prior to this time. This indicates that synthesis of Vg must be initiated sometime early in the last larval instar of female gypsy moths. Larval ovaries increased in weight throughout the last instar (from 0.29 ± 0.12 mg/pair on day 1 to 3.23 ± 0.48 mg/pair on day 10), although they did not synthesize or take up Apo-Vg prior to day 7. Vt begins to accumulate in pupal ovarian terminal follicles by day 3. The largest increases in protein content, yolk length and follicle length of the 5 terminal follicles in each ovariole occurred between days 5 and 6 post-pupal ecdysis. Pupal total ovarian weight also increased throughout development, showing a 35-fold increase between day 4 (13.7 ± 1.8 mg/pair) and day 10 (467.3 ± 59.0 mg/pair). The above results indicate that initiation of Vg synthesis and ovarian Vt uptake are temporally and developmentally separate events in the gypsy moth.