Haemolymph vitellogenin,juvenile hormone,and oöcyte growth in the adult cockroach Nauphoeta cinerea during first pre-oviposition period

In the cockroach Nauphoeta cinerea the incorporation of a protein of low solubility into the oöcytes begins at day 5 of its adult life. An immunologically identical protein appears in the haemolymph two days earlier. The concentration of this protein, i.e. ‘vitellogenin’ in the haemolymph increases up to the onset of yolk incorporation into the oöcytes. During ovarian development no correlation could be detected between vitellogenin titre and several other parameters (ovary dry weight, length of the basal oöcytes, haemolymph protein concentration, body weight and age when ovulation occurred). In young females vitellogenin titre depends on the age, i.e. the volume of the corpora allata and hence on the presence and the titre of JH. During the period of egg maturation the total haemolymph protein concentration generally tends to drop while materials not precipitable by trichloracetic acid circulate at higher concentration after ecdysis and before ovulation.Early decapitation prevents vitellogenin synthesis and oöcyte growth, but when JH is applied to decapitated females, the normal vitellogenin titre is re-established, ovarian development, however, cannot be fully resumed. A dose-response curve shows that serial application of the hormone is much more effective than single large doses. Farnesylmethylester, a JH mimic, is about a hundred times less active, but more persistent than JH. Copulation seems to enhance the synthesis and release of endogenous JH, while food and water uptake are necessary to guarantee and optimal ovarian development. JH and high vitellogenin titre never restore ovarian development in females deprived of food and/or water or in those decapitated shortly after ecdysis.     

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.     

Ecdysteroids during oögenesis in the ovoviviparous cockroach Nauphoeta cinerea

By using thin-layer chromatography and high-pressure liquid chromatography combined with radioimmunoassay as well as gas chromatography-mass spectrometry we have identified and quantified ecdysteroids in ovaries and haemolymph of adult female Nauphoeta cinerea. Our analyses demonstrate the presence of ecdysone and 20-hydroxyecdysone, the latter being clearly predominant in all stages investigated. Titre determinations of free ecdysteroids in ovaries show that the 20-hydroxyecdysone concentration is highest (approximately 400 ng/g) at the beginning of chorion formation, suggesting an involvement in this process. Towards ovulation, the titre of free ecdysteroid drops and is low in the newly ovulated egg case. Measurement of immunoreactive highly polar products demonstrates that their concentration remains on a low level throughout the oöcyte maturation period; hydrolysis experiments with Helix pomatia enzymes reveal that, compared to the free ecdysteroids in the ovary, only small quantities of ecdysteroids are present as Helix hydrolysable conjugates. If one compares the quantities of free ecdysteroids in the ovary with those in the haemolymph it becomes apparent that the concentration in the haemolymph is about 10 times lower than that in the ovary.In vitro incubation of follicle cells from oöcytes at stages around chorion formation reveals that these cells are able to produce ecdysone and 20-hydroxyecdysone, and incubation with [³H]-ecdysone demonstrates that ecdysone is efficiently converted to 20-hydroxyecdysone in a stage-dependent manner. These observations strongly suggest that the follicle cells are the site of ecdysteroid biosynthesis and of C-20-ecdysone hydroxylation.A comparison of these findings with observations made of other insects such as locusts and mosquitoes demonstrates significant differences in quality, composition, titre fluctuation and distribution of ecdysteroids in adult females from different species and suggests that these ecdysteroids might fulfil multiple and various biological functions.     

Factors responsible for the initiation of a second oöcyte maturation cycle in the ovoviviparous cockroach Nauphoeta cinerea

The factors responsible for the initiation of a second oöcyte maturation cycle were investigated by measuring oöcyte growth, vitellogenin titre, and corpus allatum activity after injection of juvenile hormone and/or removal of the egg-case from pregnant females and by performing ovary and corpus allatum transplant experiments.Egg-case removal in late pregnancy results in immediate oöcyte growth, whereas in early pregnancy oöcyte growth is resumed only after a lapse of time, even after injection of juvenile hormone. This, however, induces an immediate increase in the haemolymph vitellogenin titre. A single injection of 2 or 10 μg of juvenile hormone II first stimulates some oöcyte growth after this lapse of time and later activates the corpora allata, which in turn leads to completion of oöcyte maturation. A repeat injection of 10 μg stimulates continuous oöcyte growth without activating the corpora allata. In the presence of an egg case, activation of the corpora allata is suppressed, even after injection of 2 μg of juvenile hormone III, and the oöcytes do not grow. Injection of higher doses stimulates oöcyte growth and leads to expulsion of the egg case in up to 95% of the females. This, however, is not a direct consequence of the increase in size of the ovaries. Ovary transplant experiment show that in young pregnant females the second generation of oöcyte is not yet competent for growth and that ovaries which are competent can mature in young pregnant females, treated with juvenile hormone, whose egg case has been removed.The results are summarized in a model demonstrating the various factors involved in regulating corpus allatum activity in oöcyte maturation and pregnancy and after application of juvenile hormone. We prepose that the corpus allatum activating effect of exogenous juvenile hormone is mediated by the growing oöcyte and that this activation can be suppressed by the continuous presence of exogenous juvenile hormone.     

Inhibition of oöcyte development during pregnancy in the cockroach Eublaberus posticus

The corpora allata are inhibited during pregnancy in ovoviviparous Eublaberus posticus, and yolk is not deposited in the basal oöcytes for the entire or almost the entire gestation period.Precocious oöcyte development occurs if the oötheca is removed but this can be prevented by substituting a plastic oötheca for the true egg case in the uterus. Implantation of a uterus containing an oötheca into the abdomen of a female whose oötheca is removed does not prevent precocious oöcyte development even though many of the eggs in the implant grow and stretch the donor uterus. These experiments argue against the hypothesis that an ‘agent’ from the uterine eggs or stretched uterus inhibits the activity of the corpora allata (CA), and supports the hypothesis that inhibition from the uterus is mechanical.Cyclical activity of neurosecretory cells in certain abdominal ganglia in one species of ovoviviparous cockroach has been correlated with the cyclical inhibition of the oöcytes during pregnancy. Mechanoreceptors are found in the uteri of several ovoviviparous species including Eublaberus.In Eublaberus transecting the nerve cord between various ganglia in pregnant females only results in a marked decrease in the percentage of famales showing precocious oöcyte development when the nerves posterior to the sixth abdominal ganglion are severed. However, the results are the same if these nerves are severed after removing the oötheca. It is suggested that pressure of the oötheca on mechanoreceptors in the uterus, or cessation of pressure (after removal of the oötheca), result in sensory information being transmitted to the last abdominal ganglion which affect the CA, perhaps indirectly by controlling the activity of the neurosecretory cells in various abdominal ganglia.     

Ecdysone,juvenile hormone and oögenesis in Rhodnius prolixus

Oviposition and oögenesis can be inhibited in female Rhodnius prolixus by ecdysone given by the digestive tract. The inhibition is dose-dependent, and doses higher than 4.0 ng ecdysone/mg body weight drastically reduce the size and shape of the whole ovaries. In ecdysone-treated insects, normal oviposition and oögenesis can be re-established by a subsequent blood meal without ecdysone, or by the application of a juvenile hormone analogue.These results suggest that ecdysone inhibits juvenile hormone production.     

Initiation and regulation of oöcyte growth by the brain and corpora allata of the cockroach,Nauphoeta cinerea

Oöcytes of Nauphoeta cinerea begin to grow about 2 days after adult ecdysis. This growth can be totally prevented by surgical ablation of the corpora allata (CA) before day 2 and restored in a dose-related manner by injection of juvenile hormone (JH). Ovarian maturation can also be prevented in some animals by brain extirpation within a day of adult ecdysis but proceeds normally in others, indicating that the brain acts to promote oöcyte lengthening very soon after emergence. Wounding (mouthparts removal) blocks ovarian maturation in a similar percentage of animals, indicating that the ‘wounding effect’ is mediated by the brain. However, those wounded animals which do develop oöcytes do not reach normal values by autopsy on day 7, suggesting a temporary inhibition of the CA. Because the effects of head ligation, which effectively removes the brain as well as the CA, can be reversed by only a little more JH than the effects of allatectomy, we conclude that the primary rôle of the brain is to control the CA. We suggest that both stimulatory neurohumoral material and inhibitory nervous transmission may be utilized for this control.     

Study of oöcyte growth within the ovariole in a stick-insect, Clitumnus extradentatus

Growth of the sub-terminal follicle is hindered by the terminal oöcyte itself during maturation until its ovulation. An inhibition identical to that exercised by the sub-terminal oöcyte exists at the level of the third follicle. The inhibitory substance passes from one oöcyte to the next through the interfollicular tissue. Sub-terminal oöcytes have no particular action on the terminal follicles.Vitellogenesis requires stimulation from the tissues proximal to the ovariole. Both the oviduct and the interfollicular tissue could play a role in this stimulation. Chorionation is seen to be an autonomous mechanism.     

Effects of food and water availability,and of NCA-1 section,upon juvenile hormone biosynthesis and oöcyte development in adult female Periplaneta americana

The combined stimuli from feeding, drinking, mating and crowding are required for the highest rates of oöcyte development in maturing adult female Periplaneta americana. A graded series of “sexually suppressed” females can be produced by withholding one or more of these stimuli, and this stepwise retardation of ovarian development appears to be achieved by a progressive increase in corpus allatum restrain. It seems that all of these environmental cues are centrally integrated such that juvenile hormone-dependent processes can proceed at an appropriate pace. Water availability is evidently the most important factor. Water-deprived females are sexually unreceptive, and are found to have very low rates of juvenile hormone biosynthesis and ovarian development. This holds true even when they are provided with food. In contrast, 75% of starved females are sexually receptive if allowed free access to drinking water. At the same time they have enhanced corpus allatum activity, and show significant oöcyte growth.The mode of regulation of corpus allatum function in adult female P. americana appears to be significantly different to the model proposed for the cockroaches Leucophaea maderae and Diploptera punctata. Allatotropic signals may be more important than inhibitory signals in the former species. The glands continue to be moderately active in fed, mated female P. americana after NCA-1 section (although a major peak of corpus allatum activity is not obvious), and the rate of oöcyte development is not greatly reduced. However, NCA-1 mediated inhibition of juvenile hormone biosynthesis is less readily demonstrated. We could observe no enhancement of corpus allatum activity nor stimulation of oöcyte growth after unilateral NCA-1 section when the operation was performed on starved virgins, and the same result was found after bilateral NCA-1 section when starvation or virginity were separately enforced. A slight stimulation of juvenile hormone biosynthesis, together with a small increase in oöcyte development, could only be demonstrated after both NCA-1 were cut in starved virgins.We conclude that neurally mediated corpus allatum inhibition in has yet to be adequately verified, and that the available evidence does not contradict the theory that juvenile hormone biosynthesis in adult females could be regulated predominantly by chemicals released into the haemolymph.     

Initiation and termination of host-seeking inhibition in Aedes aegypti during oöcyte maturation

The inhibition of host-seeking behaviour that accompanies vitellogenesis in the mosquito, Aedes aegypti, was examined by the removal and implantation of ovaries. Mosquitoes ovariectomized before a blood meal and between 1 and 6 hr after a blood meal responded to a host at 48 hr after a blood meal. However, when ovariectomy was delayed until 10 hr after the meal or later, most mosquitoes did not respond to the host. When a partial ovary was present for only the first 12 hr after a meal, there was no host-seeking inhibition at 48 hr, and only 58% of females with one complete ovary present during this time interval responded. Howver, these same amounts of ovarian tissue inhibited host-seeking when they remained for 48 hr after a meal. Vitellogenic ovaries from donors blood-fed 8–24 hr before, implanted into sugar-fed recipients, did not affect the host-seeking behaviour of these recipients. Ovaries removed and reimplanted before the blood meal inhibited host-seeking at 72 hr after the blood meal only in the absence of oviposition from intact ovaries. It is concluded that 2 humoral factors are involved in the promotion of host-seeking inhibition: the first factor is produced by the ovaries, and after reaching a critical threshold in the haemolymph, stimulates the release of a second factor that acts directly to inhibit mosquito behaviour. An ovary which retains 2 or fewer eggs after oviposition terminates the inhibition via nervous pathways. The role of 20-hydroxyecdysone in the behavioural inhibition is discussed.     

Precocene I and II inhibition of vitellogenic oöcyte development in Drosophila melanogaster

Adult female Drosophila melanogaster were exposed to precocene I and II, antiallatropin compounds which result in juvenile hormone deficiency in many insects. The presence of juvenile hormone in Drosophila adults was evaluated by examining vitellogenic oöcyte development, a process regulated by juvenile hormone in these flies. Both precocenes reduced the number of vitellogenic oöcytes present 43 hr after exposure in a dose-dependent manner. Precocene I was effective when applied to either newly eclosed females prior to vitellogenic oöcyte development or to gravid females. Precocene I was also effective in decapitated females, indicating that the action of the compound is not mediated by the brain. Corpus allatum volume, presumably a reflection of secretory activity, increased between 0 and 24 hr after eclosion in control females but not in precocene-treated females even after 48 hr. However, when females were removed from precocene medium, gland volumes increased within 48 hr to approximately those of control flies. This result is consistent with the reversibility of the precocene effect on Drosophila adults. These results suggest that precocene acts on the corpus allatum of Drosophila adult females to produce juvenile hormone deficiency.     

Effects of starvation and feeding upon corpus allatum activity and oöcyte growth in adult female Periplaneta americana

Direct radiochemical determinations of juvenile hormone (JH) biosynthesis by corpora allata (CA) isolated from starved and re-fed Periplanteta americana have been employed to elucidate the humoral mechanisms involved in the modulation of reproductive activity in response to food availability. When starvation was initiated in mature adult females at the time of formation of an oötheca the next oötheca was normally deposited 5 to 6 days later, a delay of 2–3 days, and a third oötheca was formed by only 50% of starved females. The terminal oöcytes in the remaining females were either resorbed or maintained in an arrested state. Ovarian development had effectively ceased after 2 weeks of starvation but recommenced within 3 days of re-feeding. The CA of most starved females exhibited 2 activity cycles following food withdrawal. The first peak occurred on day 1 of the starvation period and was coincident with the timing for fed controls. The second peak was delayed by about 2 days and the activity of the CA then declined to the extent that glands from animals starved for more than 11 days were completely inactive. Feeding, after 10 or 16 days starvation, resulted in a resumption of CA activity which was detectable in some animals within 24 hr, and very high rates of JH biosynthesis were found 4 or 5 days later. The results suggest that P. americana can readily and efficiently modulate egg production in response to food supply, and that control is effected through alterations in JH production by the CA. The use of farnesenic acid as a biochemical probe indicates that CA inactivity after long periods of starvation does not arise because malnutrition has caused complete metabolic shut-down in the glands, and that JH biosynthesis is basically modulated at a control point prior to the last two enzymic stages in the pathway.     

Corpus allatum activity during overlapping cycles of oöcyte growth in adult female Melanoplus sanguinipes

Cycles of oögenesis in Melanoplus sanguinipes overlap to the extent that there are always 2 and occasionally 3 sets of vitellogenic oöcytes in the ovarioles at any one time. Three phases of vitellogenic oöcyte development can be distinguished: (1) An initial 24-hour phase of slow development (1.0–1.2 mm, 0.05–0.10 mm³). (2) A phase of rapid oöcyte growth (1.2–3.5 mm, 0.1–1.3 mm³). The duration of this phase is 2 days in the first cycle and 3 days in subsequent cycles. (3) A final phase of rapid oöcyte growth and maturation (3.5–4.5 mm, 1.3–2.8 mm³). Including the time taken for oviposition the duration of this latter phase is 3 days. Phases 1, 2 and 3 of cycles n + 2, n + 1 and n, respectively, overlap entirely. Activity of the corpora allata was measured using a radio-biosynthetic technique. A period of increased corpus allatum activity coincides with the initial part of phase 2 in each cycle. Each set of oöcytes is, thus, subject to 2 and occasionally 3 peaks of corpus allatum activity during development. Using these data a model of the control of oöcyte development has been devised     

Changes in follicle cell morphology,ovarian protein synthesis and ovarian DNA synthesis during oöcyte maturation in Leucophaea maderae: Role of juvenile hormone

Changes in follicle cell morphology were correlated with changes in rates of protein synthesis and DNA synthesis by the ovary during ovarian maturation in Leucophaea maderae. During the vitellogenic period of oöcyte development, which lasts approx, 15 days, morphological changes in the follicle cells are accompanied by moderate rates of ovarian protein synthesis and rapid rates of ovarian DNA synthesis. At approx. 15 days after mating, the shape of the follicle cells changes from cuboidal to squamous, ovarian DNA synthesis is arrested, and ovarian protein synthesis increases slightly. During the final period of oöcyte development, which lasts approx, two days, the interfollicular channels between the follicle cells have disappeared and the squamous follicle cells, which contain an extensive rough endoplasmic reticulum, deposit a chorion around the mature oöcyte. These morphological changes are accompanied by a radical increase in ovarian protein synthesis, while ovarian DNA synthesis remains arrested. Immediately before ovulation, ovarian protein synthesis starts to decline, reaching a minimal level 24 hr post-ovulation.Ovarian maturation is dependent on the presence of juvenile hormone (JH) only during the vitellogenic stage of oöcyte development. Decapitation of insects at any point during the first 10 days after mating arrests the synthesis of DNA and retards the synthesis of protein by the ovary, resulting in degeneration of the oöcyte. Subsequent injection of JH restores both events to normal levels within 72 hr. Decapitation on or after the tenth day following mating does not alter normal oöcyte development, chorion deposition, ovulation or egg case formation.Primary induction of protein synthesis in ovaries from virgin females can be achieved by either an in vivo or in vitro exposure of the tissue to JH, thus confirming a site of action for JH to be ovarian tissue. Electrophoretic analysis of the soluble proteins from JH-exposed ovaries in vivo reveals that JH stimulates general protein synthesis, rather than the synthesis of a specific major protein such as vitellogenin.     

Uptake of vitellogenin into developing oöcytes of Locusta migratoria

The selective incorporation of vitellogenin into developing locust oöcytes was studied using ¹²⁵I-vitellin. Vitellogenin incorporation does not start before the oöcytes are 1.5 mm in length. It increases rapidly up to a maximum at 4.7 mm oöcyte length and decreases steadily until the eggs are fully developed (6.5 mm). Concentrations of serum proteins and vitellogenin in the haemolymph show parallel changes, vitellogenin titre reaching a maximum of 7.5 mg/ml. Incorporation rates for vitellogenin increase from 1.5 μg/hr/oöcyte (2.2 mm) up to 13.8 μg/hr/oöcyte (4.7 mm). In this range incorporation per unit surface area increases 4-fold. While the vitelline and chorionic membranes are being formed, the incorporation rates as well as the protein concentrations in the haemolymph decrease steadily until the second gonotrophic cycle starts. The hormonal basis for oögenesis and the mechanism for selective uptake of locust vitellogenin are discussed.     

Hormonal aspects of oögenesis in the flies Phormia regina and Sarcophaga bullata

The corpora allata (CA) and median neurosecretory cells (MNC) of Phormia regina and Sarcophaga bullata become active with increasing age of the fly, on a diet of sugar alone. To prevent or retard oögenesis the CA or MNCs must be removed shortly after emergence, with subsequent protein meals. Topical JH application partially compensates for CA or MNC removal. This shows that the MNC activate the CA, and not vice versa. The trauma of either operation slightly depresses egg development.Injection of ecdysone into both species in the stage of initial yolk deposition causes the primary oöcytes to degenerate. This leads to development of the penultimate oöcytes. Older and younger egg stages are not sensitive to ecdysone. In P. regina the application of JH to females with developing primary oöcytes stimulates yolk deposition in the penultimate oöcytes.     

Effects of electrocoagulation of cerebral neurosecretory cells and implantation of corpora allata on oöcyte development in Locusta migratoria

The implantation of active corpora allata into intact Locusta females during growth accelerates pre-vitellogenic oöcyte growth and vitellogenesis. Localised stimulation of yolk deposition follows the implantation of active corpora allata between the ovarioles demonstrating a gonadotrophic rôle for the corpus allatum hormone. Electrocoagulation of the median neurosecretory cells of the brain prevents vitellogenesis whilst pre-vitellogenic oöcyte growth occurs normally. Implantation of active corpora allata into females with ablated cerebral neurosecretory cells promotes vitellogenesis in a proportion of test animals although mature oöcytes are never produced.It is suggested that the rôle of the median neurosecretory cells during egg development in Locusta is primarily concerned with the activation and maintenance of activity of the corpora allata. The corpus allatum hormone acts both metabolically and gonadotrophically.     

Effects of juvenile hormone I and the anti-juvenile hormone fluoromevalono-lactone on development and juvenile hormone esterase activity in post-feeding last-stadium larvae of Trichoplusia ni (Hübner)

Treatment of post-feeding (early day 3; wandering phase) last-stadium larvae of the cabbage looper, Trichoplusia ni, with the anti-juvenile hormone, fluoromevalonolactone, prevented the normal ecdysis to the pupa. It caused the formation of larval-pupal intermediates, a dose-dependent delay in the time of tanning, and a decrease in juvenile hormone esterase activity at the time of the prepupal juvenile hormone esterase peak. Fluoromevalonolactone was inactive as juvenile hormone esterase inhibitor in vitro. Conversely, juvenile hormone I accelerated the time of tanning, induced the early appearance of juvenile hormone esterase activity, and prevented adult eclosion. Although most of the larvae that were treated with fluoromevalonolactone immediately after the prepupal burst of juvenile hormone (late on day 3; post-spinning phase) still became larval-pupal intermediates, the time of tanning and juvenile hormone esterase activity were close to normal. Topical treatment of day-3 larvae with radiolabelled juvenile hormone I resulted in the rapid appearance and decline of radiolabelled juvenile hormone I in the haemolymph which was associated with the increased production of juvenile hormone I acid and the induced appearance of juvenile hormone esterase activity. Thus, in post-feeding last-stadium larvae of T. ni, juvenile hormone seems to be necessary for the proper formation of the pupa. Juvenile hormone is also involved in determining the time of pupation, and it appears to induce its own degradation.     

Vitellin and vitellogenin incorporation by isolated oöcytes of Locusta migratoria migratorioides (R.F.)

Vitellin and vitellogenin labelled in vitro with ¹²⁵I and in vivo with ³H were incorporated into yolk by locust oöcytes incubated in an in vitro system. This incorporation was specific and linear with the duration of incubation. Uptake of vitellin by oöcytes was 3–4 times higher than ¹²⁵I-bovine serum albumin in 2.1-mm oöcytes and 20 times higher than ¹²⁵I-bovine serum albumin in 4.0-mm long oöcytes. The uptake of the albumin was enhanced by the presence of vitellin in the incubation medium. ³H-labelled yolk protein was incorporated at higher rates than that labelled with ¹²⁵I. The addition of the juvenile hormone analogue ZR 515, caused the incorporation rates of vitellogenin to be increased. The amount of vitellin or vitellogenin taken up by the oöcytes increased with their length, and the rate of incorporation per unit surface area was highest in 3–4-mm long oöcytes. These results corroborate previously reported in vivo patterns of incorporation rates of developing oöcytes.