Lipophorin-facilitated hydrocarbon uptake by oocytes in the German cockroachBlattella germanica(L.)

Abstract

SUMMARYLarge amounts of hydrocarbons accumulate during vitellogenesis in the developing basal oocytes of the German cockroach Blattella germanica (L.), and all ovarian hydrocarbons are deposited into an egg case (ootheca) during oviposition. Hydrocarbons are not synthesized by the ovaries, but are delivered by hemolymph lipoproteins and accumulate within the basal oocytes. A native B. germanica hydrocarbon, [3H]3,11-dimethylnonacosane, injected into adult females of various ages, was taken up by the ovaries in relation to oocyte growth. Ovarian uptake of the hydrocarbon was low in day 0–1 females, increased dramatically between days 3 and 6 and declined sharply through oviposition on day 8–9; ovarian uptake of the hydrocarbon was low during a 21-day pregnancy that followed. [1-14C]Propionate, which becomes incorporated into methyl-branched hydrocarbons, was injected into 5-day-old vitellogenic females to monitor the de novo biosynthesis of hydrocarbons and the time course of hydrocarbon deposition in the ovary. Propionate was rapidly incorporated into hydrocarbons within 4 h. Hydrocarbon uptake by the ovaries, however, was three times higher 24 h after injection than 4 h after injection, showing that hydrocarbons are slowly and continuously deposited in oocytes. This result was confirmed with topical application of [3H]3,11-dimethylnonacosane: ovarian uptake was three times higher after 24 h than after 4 h. In vitro incubations of sternites, which synthesize hydrocarbons, with [14C]propionate and ovaries, showed that both hemolymph and purified high-density lipophorin facilitated ovarian uptake of newly synthesized hydrocarbons; maximum uptake occurred with 10 % hemolymph or 1 mg ml–1 high-density lipophorin. These results were confirmed with sternites treated with [3H]3,11-dimethylnonacosane and co-incubated with ovaries. This is the first report to show that copious amounts of maternal hydrocarbons are provisioned in oocytes and to demonstrate the existence of a hydrocarbon transport pathway involving hemolymph high-density lipophorin.