The ovary as a source of alpha-ecdysone in an adult mosquito.

Abstract

The ovaries of the mosquito Aedes aegypti cultured in vitro secrete material that behaves like ecdysone in a radioimmunoassay. The material was identified as aecdysone by high-resolution liquid and gas-liquid chromatography. Secretion reached a maximum 16 hr after a blood meal as shown by bioassay and direct determination. Ovariectomy reduced the concentration of ecdysone in the adult after a blood meal. Qualitative analysis of whole-body extracts indicated fi-ecdysone to be the principal species present. Thus the ovaries appear to secrete a prohormone, a-ecdysone, which is converted to,-ecdysone. ,-ecdysone plays a significant role in stimulating egg development in the adult mosquito and may have reproductive roles in other insects.In mosquitoes the blood meal triggers egg development. This process, which has been found to be quite complex (1), involves the elaboration of yolk for later use by the developing embryo. The major proteins which become yolk are synthesized by the fat body, secreted into the hemolymph, and selectively taken up by the developing oocyte (2, 3). These proteins have been termed vitellogenins (4). Recent investigations into the control of this process showed that, in contrast with most insects, the mosquito ovary was the source of a hormonal factor which activated and maintained vitellogenin synthesis by the fat body (5). Thus synthesis by the fat body was abolished by ovariectomy and restored by reimplantation. Further, when ovaries from blood-fed females were incubated in vitro with the inactive fat body from unfed females, synthesis of vitellogenin was activated. This ovarian hormone was designated the vitellogenin stimulating hormone, VSH (1).The discovery that injected f3-ecdysone stimulates egg development (6) and dopa decarboxylase activity (7) in the absence of a blood meal led us to investigate the possibility that VSH might be f3-ecdysone. Our results indicated that f3-ecdysone mimicked VSH in vivo and in vitro (8) and that material with ecdysone-like activity could be detected in mosquitoes after a blood meal (9). These lines of evidence strongly suggested that VSH was fl-ecdysone or a closely related steroid. We here describe experiments designed to identify the secretory product of the ovary. METHODSMosquitoes (Aedes aegypti) were reared at 27 + 0.50 using standard techniques (8, 9). The assay for vitellogenin synthesis has been described in detail (1, 8). The radioimmunoassay (RIA) was performed as previously described (10, 11).Ovaries were removed from females 15 hr after a rabbit blood meal and incubated at 250 with gentle shaking in groups of 100 in 100,ul of a defined medium (8). After 24 hr the medium was removed and the ovaries were rinsed with saline. An equal volume of methanol was added to the combined medium and rinse. Particulates were removed by filtration. The extract was evaporated to dryness under reduced pressure, redissolved in chloroform:methanol (2:1) and partitioned against water according to Folch et al. (12). The epiphase was dried under vacuum ...

Postemergence growth of the ovarian follicles of Aedes aegypti

“…1). The 36 hr lag in growth rate after a blood meal is about the amount of time that ecdysone titres are high in the mosquito (HAGEDORN et al, 1975).…”

Ecdysterone Biosynthesis: A Microsomal Cytochrome-P-450-Linked Ecdysone 20-Monooxygenase from Tissues of the African Migratory Locust

“…It may well appear that various oxygenation steps from a sterol precursor to ecdysone in prothoracic glands are also dependent on cytochrome P-450 monooxygenases. Similarly, the synthesis of ecdysteroids in abdominal tissues [46] and adult ovaries [47,48] may also prove to be dependent on cytochrome P-450. Moreover, data of Hammock [49] on the epoxidation of methyl farnesoate by cockroach corpora allata are strongly suggestive of a cytochrome P-450 involvement in juvenile hormone synthesis.…”

Cyclicity of mosquito vitellogenic ecdysteroid-mediated signaling is modulated by alternative dimerization of the RXR homologue Ultraspiracle

“…After 3 days of PV development, the fat body and ovary enter a state of arrest that persists until a blood meal is taken, which triggers the release of the ovarian ecdysteroidogenic hormone from the medial neurosecretory cells of the brain for up to 12 h after feeding (5,6). In response to ovarian ecdysteroidogenic hormone, the ovary produces ecdysone, which is converted into an active form of the hormone 20E (7). 20E titers are only slightly elevated at 4 h postblood meal (PBM), they begin to rise sharply at 6-8 h PBM, and they reach their maximum level at 18-24 h PBM.…”