Nonvitellogenic female sterile mutants and the regulation of vitellogenesis in Drosophila melanogaster.

The genetic and endocrine regulation of vitellogenesis was investigated by studying 18 female sterile mutations that disrupt the development of normal vitellogenic follicles. Applications of exogenous juvenile hormone analog and reciprocal ovarian transplants between flies of different genotypes were employed to accomplish our first two objectives: to find (1) whether the mutation blocked development of the ovary directly, and (2) whether the mutation altered the hormonal milieu. In 15 of the mutants the developmental defect was localized to the ovary, but in the other 3 the ovary was competent to respond to a permissive environment. The internal milieu of these three mutants (ap⁴, fs(3)A1, fs(2)A18) was unable to provoke normal development in wild-type ovaries, suggesting that these mutations cause endocrine defects. Our third objective was to find whether an endocrine organ was itself defective in any of these mutants. The corpus allatum from two of the mutants was unable to provoke vitellogenesis in isolated wild-type abdomens, but corpora allata from wild-type females or from other mutants were able to promote maturation of ovarian follicles in isolated abdomens. Our fourth objective was to find whether any of the mutants were able to produce yolk proteins. Immunoelectrophoresis of fly hemolymph demonstrated that in all mutants tested vitellogenins were found in the blood. These experiments permit four main conclusions. First, they identify the first Drosophila mutants in which an endocrine gland is shown to be intrinsically defective during adulthood. Second, they show that the production of morphologically normal late previtellogenic follicles is not required for the induction of vitellogenin synthesis and secretion. Third, they show that juvenile hormone can cause ovarian follicles to sequester yolk in mutant flies. And finally, they show that mutants with defective corpora allata still synthesize and secrete vitellogenin. Taken together, these conclusions suggest that in Drosophila melanogaster the uptake of vitellogenin into follicles depends upon the availability of juvenile hormone, but that the synthesis and secretion of vitellogenin are independent of both normal ovaries and totally normal corpora allata.     

The Regulation of yolk polypeptide synthesis in Drosophila ovaries and fat body by 20-hydroxyecdysone and a juvenile hormone analog

In adult female Drosophila melanogaster an increase in the synthesis and secretion of three yolk polypeptides (YPs) occurs during the first 24 hr after eclosion. During organ culture, these same polypeptides are synthesized and secreted into the medium by both fat body and ovaries. Two hormones, 20-hydroxyecdysone (20-HE) and a juvenile hormone analog (ZR-515) stimulate synthesis and secretion of YPs into the hemolymph of isolated female abdomens. The present experiments were undertaken to compare synthesis of YPs in normal females with YP synthesis in preparations deprived of anterior endocrine glands, and to find which hormone stimulates synthesis in the different organs. Separation of hemolymph proteins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed that at eclosion incorporation of [³⁵S]methionine into YP1 and YP2 was low and was barely detectable in YP3. Over the next 24 hr the rate of label incorporation increased for all the YPs. Isolation of female abdomens at eclosion prevented this increase in label incorporation but did not entirely abolish YP synthesis. Application of either ZR-515 or 20-HE to isolated abdomens stimulated up to ninefold label incorporation into three polypeptides which comigrated with YPs from normal vitellogenic females. The response of isolated abdomens to ZR-515 or 20-HE was first detectable between 90 and 135 min after hormone application. The stimulated bands were confirmed to be YPs by a comparison of peptide digests of each of the three labeled polypeptides with those of the yolk polypeptides from intact vitellogenic females. The hypothesis that the two hormones might act on different organs was tested by treating isolated female abdomens with various concentrations of either ZR-515 or 20-HE and then culturing the stimulated organ in vitro with [³⁵S]methionine. The fat body responded to both hormones by synthesizing and secreting into the culture medium polypeptides which comigrated with the YPs found in hemolymph, whereas the ovary produced similar polypeptides only after ZR-515. These secreted polypeptides were confirmed to be YPs by repeating the experiment using organs from heterozygotes for both YP2 and YP3 electrophoretic variants. Such organs synthesized five polypeptides which comigrated with the corresponding yolk polypeptides. These findings are discussed in relation to a hypothesis for the action of the two hormones.     

Role of juvenile hormone in the synthesis and sequestration of vitellogenins in the red cotton stainer, Dysdercus koenigii (Heteroptera: Pyrrhocoridae)

Investigations were carried out to determine the role of juvenile hormone (JH) and 20-hydroxy ecdysone in the synthesis and uptake of vitellogenins, which were earlier identified, purified and characterised, in Dysdercus koenigii. The concentration(s) of vitellogenin(s) in fat body, haemolymph and that of vitellin(s) in ovary were significantly lower after chemical allatectomy at eclosion. In addition, at 70 h after emergence, chemical allatectomy reduced ovarian vitellin concentration, but vitellogenin levels remained normal in the fat body and haemolymph. The haemolymph vitellogenins were not incorporated into oocytes in such insects. Administration of JH-III at 20 h after allatectomy restored vitellogenin levels in the fat body and haemolymph, but the ovary failed to incorporate the available vitellogenins from haemolymph in such insects. However, when JH-III was administered twice, one at 20 h and then at 70 h after allatectomy, vitellogenin concentrations in fat body and haemolymph and also vitellin concentrations in ovary approached control levels. It is suggested that JH has two separate roles, one in vitellogenin synthesis and the other in uptake. 20-hydroxy ecdysone had no apparent role in either vitellogenin synthesis or uptake in D. koenigii.     

Control of oocyte maturation in sexually mature Drosophila females

In many sexually mature insects egg production and oviposition are tightly coupled to copulation. Sex-Peptide is a 36-amino-acid peptide synthesized in the accessory glands of Drosophila melanogaster males and transferred to the female during copulation. Sex-Peptide stimulates vitellogenic oocyte progression through a putative control point at about stage 9 of oogenesis. Here we show that application of the juvenile hormone analogue methoprene mimics the Sex-Peptide-mediated stimulation of vitellogenic oocyte progression in sexually mature virgin females. Apoptosis is induced by 20-hydroxyecdysone in nurse cells of stage 9 egg chambers at physiological concentrations (10(-7) M). 20-Hydroxyecdysone thus acts as an antagonist of early vitellogenic oocyte development. Simultaneous application of juvenile hormone analogue, however, protects early vitellogenic oocytes from 20-hydroxyecdysone-induced resorption. These results suggest that the balance of these hormones in the hemolymph regulates whether oocytes will progress through the control point at stage 9 or undergo apoptosis. These data are further supported by a molecular analysis of the regulation of yolk protein synthesis and uptake into the ovary by the two hormones. We conclude that juvenile hormone is a downstream component in the Sex-Peptide response cascade and acts by stimulating vitellogenic oocyte progression and inhibiting apoptosis. Since juvenile hormone analogue does not elicit increased oviposition and reduced receptivity, Sex-Peptide must have an additional, separate effect on these two postmating responses.     

Hormonal control of vitellogenin synthesis in Oncopeltus fasciatus

Previous work indicated the existence of two vitellogenins (A and B) in the haemolymph of Oncopeltus fasciatus, and that vitellogenin B was juvenile hormone (JH)-dependent whereas A was not (Kelly and Telfer, 1977). We have extended these results using several electrophoretic techniques in combination with limited proteolysis of key proteins to show that (1) vitellogenin B is present in eggs in a modified form while vitellogenin A cannot be detected in eggs. (2) Vitellogenin A may be a precursor of B since it has a molecular weight of 200,000D, approximately three times that of vitellogenin B (68,000D) and analysis by limited proteolysis shows that two proteins to be nearly identical. (3) Neither ovariectomy nor treatment with the anti-allatotropin, precocene II prohibits the appearance of vitellogenins A and B in the haemolymph. (4) Injection of ecdysone or 20-hydroxyecdysone into adult, male Oncopeltus fasciatus induces the appearance of both vitellogenin A and B in the haemolymph, suggesting the possible involvement of ecdysteroids in the control of vitellogenin synthesis in this species. (5) We have no evidence for JH control of the synthesis of vitellogenin, however, the ratio of vitellogenin A to B in the haemolymph is higher in the precocene-treated females.     

Influence of a juvenile hormone analogue on vitellogenin synthesis and oögenesis in larvae of Nauphoeta cinerea

In experiments on the synthesis of the vitellogenic protein, farnesylmethylester, a juvenile hormone (JH) analogue, was injected into female Nauphoeta cinerea larvae at various stages during their development. Two and 4 days after injection, 2 μl of haemolymph were assayed in a vitellogenin immunodiffusion test. In second last and last instar larvae less than 6 days before adult ecdysis, high doses (100 μg) of farnesylmethylester are necessary to induce vitellogenin synthesis, whereas older last stage larvae and decapitated adults respond to small doses (1 μg) with the synthesis of vitellogenin. It seems that the competence to synthesize the vitellogenic protein changes at the time of induction of the moulting process. If farnesylmethylester is injected into last instar larvae with a supposedly high titre of ecdysone, the vitellogenic protein can be detected in the haemolymph of a small percentage of animals only.Oöcyte maturation can be observed in last instar larvae injected after the fifth to ninth day with farnesylmethylester. The observed volume changes of the corpora allata suggest that an absence of JH for a short time is necessary for the oöcytes to become competent to grow. Last instar larvae treated with farnesylmethylester become larval-adult intermediates with partly developed oöcytes, demonstrating a simultaneous juvenilizing and gonadotropic influence of the JH analogue. In last instar larvae injected with farnesylmethylester a partial degeneration of already maturing oöcytes is induced at the time when the ecdysone titre is supposedly high and the possible reasons for this are discussed.     

Ovarian defects in hybrids of the species pair Drosophila virilis and Drosophila texana

In interspecific matings between Drosophila virilis and Drosophila texana female sterility is observed in F₂ hybrid females. A previous study has shown that no vitellogenin synthesis occurs in the fat body of sterile hybrid females. The results presented in this paper show that hybrid ovaries of sterile females transplanted into the abdomens of females of the parental species are not able to develop upon maturity. With few exceptions, the hybrid ovaries remained alive in the host environment, but their oocytes failed to develop to vitellogenic stages. Thus, in hybrid females between Drosophila virilis and Drosophila texana sterility is the result of defects in both the two main developmental processes of egg maturation, the synthesis of vitellogenins in the fat body and the uptake of vitellogenins by the ovary. Dev Genet 20:47–52, 1997. © 1997 Wiley-Liss, Inc.     

Vitellogenins in the firebrat,Thermobia domestica (Packard): Immunological quantification during reproductive cycles and in relation to insemination (Thysanura: Lepismatidae)

An antiserum raised against the major fractions (240 + 300 Kd) of the vitellins extracted from maturing oöcytes of Thermobia domestica, allowed the immunological relationship between these proteins and their haemolymph precursors (vitellogenins) to be established, as well as the female specificity of these protein fractions. Using rocket immunoelectrophoresis, the vitellogenin concentration in the female haemolymph was measured on each day of a reproductive cycle. The changes in vitellogenin titre appear to be correlated with ovarian maturation: very low levels during the previtellogenic phase and increasing levels during the vitellogenic growth phase of the basal oöcytes. Also, these changes are synchronized with the moulting cycles which persist in the adults of these primitive insects. An insemination at the beginning of the interecdysial period causes a large increase in the vitellogenin titre synchronized with accelerated oöcyte growth.     

Vitellogenin induced in adult male Diploptera punctata by juvenile hormone and juvenile hormone analogue: Identification and quantitative aspects

The effect of the juvenile hormone analogue hydroprene on the appearance in the haemolymph of the yolk-protein precursor vitellogenin in male Diploptera punctata has been assessed using rocket immuno-electrophoresis. Vitellogenin was induced in a dose-dependent fashion, with a minimum dose of 10 μg hydroprene required for its appearance. Implantation of male corpora allata into male and female hosts also resulted in the appearance of vitellogenin in the haemolymph of the hosts, with females showing apparent greater sensitivity to the implantation.The identity of vitellogenin in male haemolymph was further confirmed using Ouchterlony double immunodiffusion and SDS polyacrylamide gel electrophoresis of immunoprecipitates. The electrophoretic pattern of immunoprecipitated haemolymph from females and hydroprene-treated males was similar, further confirming that the immunoprecipitable product was in fact vitellogenin.     

Juvenile hormone and 20-hydroxyecdysone as primary and secondary stimuli of vitellogenesis in Aedes aegypti

Female Aedes aegypti that were fed blood and immediately abdominally ligated did not deposit yolk. Injection of 20-hydroxyecdysone (1.5–5.0 ng) or topical application of juvenile hormone (JH) analogue methoprene (25 pg) did not induce vitellogenesis in these abdomens. When blood-gorged ligated abdomens were treated with both hormones, however, vitellogenesis was stimulated in 60% of treated animals. Rocket immunoelectrophoresis indicated that vitellin concentration per follicle in treated animals was similar to that in intact controls. When ligated abdomens were first treated with methoprene and immediately injected with a crude head extract of egg development neurosecretory hormone, vitellogenin synthesis was induced at a rate similar to that in blood-fed controls. Methoprene at this concentration (25 pg), did not cause an increase in whole-body ecdysteroid titers. Larger amounts of methoprene (1.65 ng) were needed to stimulate egg development and ecdysteroid production. Implantation of ecdysone-secreting ovaries into ligated abdomens did not stimulate vitellogenesis in the recipients. However, in recipients that were first treated with methoprene (25 pg), implantation of ecdysone-secreting ovaries resulted in normal egg development. These experiments indicate that the appearance of JH precedes 20-hydroxyecdysone in stimulating vitellogenesis following blood feeding in Ae. aegypti.     

Temporal events of gypsy moth vitellogenesis and ovarian development

Abstract The vitellogenic period of gypsy moth ovarian development starts on day 3 of the pupal stage and continues through adulthood. During this period, rapid increases occur in follicle size, protein content, and wet weight of the ovary. Patency is observed on day 3 of the pupal stage.
Pre-vitellogenic follicles are formed in the last larval stadium. Newly formed follicles detach from the germarium on day 4, and increase rapidly to 140 per ovariole at the end of the last larval stadium. The pre-vitellogenic follicles are uniformly around 50 um in diameter. No vitellogenin is incorporated into the oocytes until the pupal stage.
Polyacrylamide gel electrophosesis (PAGE) in the presence of sodium dodecylsulphate (SDS) analysis of male and female haemolymph samples and vitellogenic ovaries demonstrates the presence of two female-specific subunits of vitellogenin of 180 kD and 160 kD. These proteins are detected only in haemolymph and ovarian extracts of vitellogenic females. The molecular weight of the native protein determined by size exclusion chromatography is approximately 400–420 kD.
A highly sensitive double antibody sandwich enzyme-linked immunosorbent assay (ELISA) was developed to monitor the temporal changes in vitellogenin titre in haemolymph. Vitellogenin production starts on day 2 of the last larval stadium, reaching a maximum level by day 6 of the last larval stadium, and decreasing in the late pupal stage as vitellogenin was internalized into the oocytes. This is the first report of vitellogenin production occurring in the larval stage of a holometabolous insect. The fact that vitellogenin production and uptake occur during different stages of development in the gypsy moth, opens up some interesting questions concerning the underlying regulatory mechanisms controlling each process.     

Vitellogenin titre in haemolymph of Locusta migratoria in normal adults,after ovariectomy,and in response to methoprene

Vitellogenin in the haemolymph of Locusta migratoria was assayed by rocket immunoelectrophoresis to elucidate aspects of its regulation. In many normal adult females, vitellogenin first appeared on days 5–9, rose quickly to peak levels, and declined before a second vitellogenic cycle; in others, it appeared later and built up more slowly. The timing of first appearance of vitellogenin, and proportions of early and late-developing individuals, differed markedly in groups from the same colony assayed in different years, suggesting effects of both genetic and environmental variation. Average peak levels of vitellogenin were 25–30 mg/ml. After ovariectomy, vitellogenin appeared near the normal time and increased for several weeks to about 300 mg/ml; haemolymph volume also increased greatly, so that the total haemolymph-vitellogenin pool reached about 300 mg/individual, or 100 times the normal amount. After ovariectomy, no cyclicity of vitellogenin accumulation was apparent. These results show that the ovary is not required for stimulation of vitellogenin synthesis, and suggest that normal cycling may depend on inhibition by the mature ovary. Females treated with ethoxyprecocene on day 1 of adult life to inactivate the corpora allata did not produce vitellogenin, but were induced to do so with the juvenile hormone analogue, methoprene. After injection of 150 μg of methoprene in mineral oil, there was one day lag, then vitellogenin increased in the haemolymph to the normal peak level and declined slowly to zero during 5 weeks; after a second injection of methoprene, vitellogenin re-appeared more rapidly, with less lag, reflecting accelerated secondary hormonal stimulation of vitellogenin synthesis in the fat body. Adult males showed no detectable haemolymph vitellogenin even after injection of large doses of methoprene.     

An electrophoretic study of proteins of the ovary,fat body,and haemolymph in the migratory grasshopper, Melanoplus sanguinipes

Electrophoretic separation of saline extracts from the ovary revealed 14 proteins. Twelve proteins were detected in the fat body, of which seven had electrophoretic mobilities identical to those in the ovary. Similarly, eight of 16 proteins in the haemolymph of vitellogenic females ahad electrophoretically identical counterparts in the ovary. As these proteins accumulate in the haemolymph of ovariectomized females, the findings suggest that most yolk proteins are synthesized in the fat body. Although most female haemolymph proteins are present in males, two of the predominant yolk protiens are absent and represent female-specific proteins.Although certain proteins accumulate in the haemolymph of allatectomized females, the major ovarian proteins are absent or present in low concentrations. However, 48 hr after allatectomized females are treated with a juvenile hormone analogue, the haemolymph protein pattern resembles that of a normal female. This suggests that the corpora allata stimulate the synthesis of female-specific and other vitellogenic proteins. The median neurosecretory cells (mNSC) are also necessary for synthesis of female-specific proteins. Furthermore, proteins which are present in allatectomized females are absent in mNSC-cauterized insects suggesting that the mNSC stimulate general protein synthesis.     

Hormonal regulation of phase polymorphism and storage-protein fluctuation in the common cutworm, Spodoptera litura

Three storage proteins are synthesised by Spodoptera litura last-instar larvae as detected by an antiserum against pupal fat body proteins. The putative pupal storage proteins 1 and 2, appear in the haemolymph of the last-instar larvae 36 h after ecdysis under crowded rearing conditions: they appear 1 day later in isolated conditions. The appearance of these proteins in the haemolymph is prevented by juvenile hormone treatment and enhanced by allatectomy. Injection of 20-hydroxyecdysone into ligatured larvae does not induce appearance of these 2 proteins. Accumulation of protein 3 that reacts with Bombyx mori arylphorin antiserum is not blocked by juvenile hormone and is similar in both phases. It also accumulates to a small extent in the haemolymph during the moult to the final-larval instar and then disappears at ecdysis. One-hundred ng/ml ecdysteroid caused the sequestration of these proteins by the fat body, but a higher concentration of ecdysteroid (200 ng/ml) produced pupal cuticle in the isolated abdomens, suggesting that different ecdysteroid concentrations are necessary for these two events.     

Release of egg development neurosecretory hormone in Aedes aegypti and Aedes taeniorhynchus induced by an ovarian factor

Ovariectomized Aedes aegypti do not synthesize vitellogenin after a blood meal, unless an ovary from a blood-fed donor is implanted. Decapitation, however, prior to implantation inhibits vitellogenin synthesis. A female ovariectomized and decapitated 6 hr after a blood meal, synthesizes vitellogenin if an ovary from a blood-fed donor is implanted. On the other hand, females that are fed on blood and immediately decapitated can not be stimulated to synthesize vitellogenin with implanted ovaries removed from blood-fed donors. These experiments led to the hypothesis that the blood meal stimulates the ovary to secrete a corpus cardiacum stimulating factor, that in turn promotes release of egg development neurosecretory hormone stored in the corpus cardiacum.Injection of 20-hydroxy-ecdysone or ovarian extract prepared from ovaries removed from unfed females does not release egg development neurosecretory hormone. Thus corpus cardiacum stimulating factor is not 20-hydroxy-ecdysone, and ovaries removed from unfed females do not store it.The rate of inactivation of egg development neurosecretory hormone released from the corpus cardiacum after a blood meal was investigated by implanting an ovary into females that were blood fed for various intervals than decapitated and ovariectomized. Seventy per cent of implants grow when the operation is done 18 hr after feeding, and 30% when the operation is done between 18 and 24 hr after feeding, indicating that egg development neurosecretory hormone is stable for the first 18 hr after a blood meal.Aedes taeniorhynchus females ovariectomized 24 hr after adult emergence do not synthesize vitellogenin. When such a female is implanted with an ovary removed from a sugar-fed or blood-fed Aedes aegypti donor vitellogenin synthesis is initiated, and the implant grows. Decapitation prior to implantation inhibit vitellogenin synthesis and implants do not grow. These results indicate that corpus cardiacum stimulating factor is not species specific.     

Hormonal control of storage protein synthesis and uptake by the fat body in the silkworm, Bombyx mori

The female silkworm, Bombyx mori, rapidly accumulates two storage proteins, that are synthesized by the fat body, in the haemolymph during the feeding stage of the last-larval instar, and then sequesters them from the haemolymph into fat body during the larval-pupal transformation.The rapid synthesis and uptake of storage proteins by the fat body are shown to be induced by allatectomy in the early-penultimate larval instar. A juvenile hormone analogue, methoprene, is highly effective in inhibiting the allatectomy-induced synthesis, and, in a higher dosage, further blocks the uptake. Allatectomy in the late-penultimate larval instar shortly before moulting does not enhance the storage protein synthesis, but causes the uptake to occur two days earlier in the last-larval instar. Injection of 20-hydroxyecdysone is not stimulatory for synthesis of the proteins, but is effective to induce their uptake. Starvation during the early last-larval instar completely blocks the synthesis.From these results, it is suggested that storage protein synthesis is induced in the absence of juvenile hormone by some supplementary stimulus, possibly the supply of nutrient after feeding, and uptake is induced by ecdysteroids after a decline in the juvenile hormone level.     

Juvenile hormone-induced biosynthesis of vitellogenin in Leucophaea maderae

Isolated abdomens of virgin female Leucophaea maderae, a South American cockroach, could be induced by a single injection of juvenile hormone I to synthesize vitellogenin. Synthetic capacity was assayed by removal of the fat body at various times after induction and incubation in organ culture with radioactive leucine for 5 h. Under these conditions, active tissues secrete radioactive vitellogenin into the medium after a lag of 2 h and continue secretion at a fixed rate for up to 8 h. Vitellogenin in the tissue reaches a steady-state level after about 3 h. By 5 h, approximately 80% of the newly synthesized vitellogenin can be found in the medium and constitutes 75% of the secreted protein.Vitellogenin does not appear in the medium until 18 h after juvenile hormone induction, rises to a maximum between 72 and 96 h, and has declined to half by 120 h postinduction. At the maximum, about 75% of the total protein secreted is vitellogenin, a more than 50-fold stimulation over injected controls. Since virtually the same quantitative effect of juvenile hormone was found in abdomens with and without ovaries, secondary stimulation by ovarian hormones does not appear to be involved in vitellogenin synthesis in this insect.Oocyte vitellogenin exists as a 560,000 molecular weight monomer complex and a 1,590,000 molecular weight trimer. The smaller complex is only found in young oocytes. By sodium dodecyl sulfate-gel electrophoresis, we find that the 560,000 molecular weight 14S monomer consists of four discrete peptides in the ratio A₁B₁C₂D₂ with molecular weights 118,000, 87,000, 57,500, and 96,000, respectively. The 28S trimer contains only the three peptides A, B, and C in the ratio A₁B₃C₂. These stoichiometries satisfactorily account for the molecular weights of both complexes when corrected for the lipid content. Maturation of 14S to 28S probably involves specific proteolytic conversion of D to B^D, a different peptide of the same size as B, suggesting that the true composition of 28S is A₁B₁B₂^DC₂.The 14S vitellogenin synthesized and secreted by fat body in tissue culture consists mostly of larger polypeptides. There is a major fraction of 179,000 molecular weight, a minor fraction of >260,000 molecular weight, and other smaller polypeptides. Although the exact relationship between these polypeptides and the mature subunits of vitellogenin are not yet clear, it is evident that the multiple protein subunits of this complex protein are synthesized as one or more precursor proteins, followed by proteolytic processing to the mature size.     

In vivo inhibition of vitellogenesis in the Dermapteran Labidura riparia by 20-hydroxyecdysone

In previous studies we have described the existence of cyclical changes in ecdysteroid levels during the female reproductive life of the earwig Labidura riparia. High levels of ecdysteroids are observed at the end of each vitellogenic period just before follicle degeneration, in coincidence with the beginning of each non-vitellogenic period. In the present work, using in vivo [(35)S]methionine incorporation, electrophoresis and electron microscopy, we study the effects on fat body and ovaries of 20-hydroxyecdysone (20E) injections into young vitellogenic females. This resulted in a reduction of proteosynthetic organelles (scarce Golgi complexes and fragmented RER cisternae), inhibition of vitellogenin synthesis in adipocytes, vitellogenesis arrest and premature follicular atresy. All these effects are suppressed when juvenile hormone treatment is associated with 20E injections. 20E does not inhibit vitellogenesis when applied to pars lateralis deprived females, which display continuous vitellogenesis. Thus, 20E does not act directly on ovaries nor on corpus allatum: the presence of the pars lateralis cells is required for 20E to inhibit vitellogenesis. These findings are explained in terms of the existence of a 20E feed back loop. This hormone acts via lateral neurosecretory cells of the brain which probably have an allatostatic effect.     

Vitellogenin synthesis in blood-fed Aedes aegypti in the absence of the head,thorax and ovaries

A blood meal initiates oöcyte maturation in Aedes aegypti, and we have used rocket immunoelectrophoresis to investigate the function of midgut, ovaries, and head in the onset of vitellogenin synthesis. Non-blood-fed females and those fed blood (by enema) containing soybean trypsin inhibitor never contained vitellogenin. This demonstrates that the pressure of an undigested blood meal on stretch receptors of the midgut plays no role in the induction of vitellogenin synthesis, rather the stimulus is a digestion product of blood.When females were ovariectomized or decapitated and then fed blood, the haemolymph contained newly synthesized vitellogenin 24 h later. This was also demonstrated in isolated ovariectomized abdomens. Apparently, induction of vitellogenin synthesis does not require factors from either the head, thorax, or ovaries. When ovariectomy or decapitation was postponed after a blood meal, the level of vitellogenin in the haemolymph rose. Therefore, interaction of factors from the head and ovaries maintain the synthesis needed for oöcyte maturation.     

On the relative importance of juvenile hormone and vitellogenin for oöcyte growth in the cockroach Nauphoeta cinerea

The corpora allata of castrated females of Nauphoeta grow only very slightly and do not reach a volume greater than that of the glands of normal females during gestation. These small corpora allata are, however, active and are responsible for the synthesis of vitellogenin (female specific protein) in large amounts. Besides vitellogenin the other haemolymph proteins are also synthesized and accumulated in the haemolymph in much higher concentrations than in normal females. Implanted oöcytes grow in castrated as well as in normal females at about the same rate until the tenth day of the oöcyte maturation period. Thereafter they only grow in castrated females. If castrated and normal females are decapitated, their protein content decreases. At the same time the growth stimulating capacity of their haemolymph decreases at a much faster rate. If oöcytes are implanted in castrated and decapitated females after 4 days they cannot grow any more although the vitellogenin titre of the haemolymph is still much higher than it is at any time in normal females. It can be concluded that vitellogenin alone cannot induce oöcyte growth and that juvenile hormone is necessary as well for vitellogenin synthesis as for its incorporation into the oöcytes. However, in insects rich in vitellogenin juvenile hormone leads to a more rapid oöcyte growth than in insects containing only small amounts of this protein.