| Research Abstract |
Biosynthesis of yolk protein and its hormonal regulation were investigated in the soft tick, Ornithodoros mouvata and Ornithodoros parkeri. We first purified and characterized yolkk protein, vitellin (Vn), and the hemolymph precursor of Vn, vitellogenein (Vg) from newly laid eggs and hemolymph of the tick, respectively. we demonstrated Vn and Vg are a conjugated phospho-glycoprotein associated non-covalently with haem and lipid, which molecular size is about 600 kD as native and is composed 6 polypeptides. Vg is synthesized in the fat body, secreted into hemolymph and accumulated into the developing oocytes as Vn. Vn is composed of 6 polypeptides differnt (more smaller) from that of Vg. Vg synthesis in the fat body is primarily activated by the stimulation of engorgement. After blood meal Vg appear in the hemolymph first on day 2 after engorgement and increased to very high concentration in the hemolymph (maximum 60, mugl, mul). We have tried to produce a hormone free ticks by using pr
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ecocene to study hormonal induction of Vg synthesis. We could- not produce those animals successfully, but 'we knew that precocene has no effect in lower doses (less than 100 mug/tick) and toxic in higher doses (more than 150 mug/tick) in this species of tick. But we found that one of synthetic pyrethroid, cypermethrin (CyM) has a positive effect to induce Vg synthesis and ovarian development in unengorged (both mated and virgin) adult females, and also even unengorged males and nymphs. CyM treated unengorged females produced Vg and developed ovary (but fewer eggs). This meant that unengorged females have ability to produce Vg if given a proper humoral conditions. We applied several natural juvenile hormones (JH) and JH analogs (JHA) on unengorged females, but we could not get positive effects for vitellogenesis. Therefore we concluded JH is not involved in the course of Vg synthesis induction after engorgement. From the fact that nerve activating pyrethroid, CyM, can induce vitelogenin synthesis, and from some ligation experiments we showed synganglion (SyG) has a factor which induces Vg synthesis in the fat body. We showed unengorged females treated with extract of synganglions collected from unengorged females produced Vg in significantly higher concentration than tick Ringer treated animals. We tried to purify this vitellogenesis inducing factor (VIF) and showed VIF is a polypeptids. Less
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