The effects of starvation and subsequent feeding on juvenile hormone synthesis and oöcyte growth in Schistocerca americana gregaria

The effect of starvation on the synthesis of C₁₆ juvenile hormone (JH) and the growth of terminal oöcytes was assessed in Schistocerca americana gregaria at two times during adult life: before activation of the corpora allata and during the first gonotrophic cycle. In both groups, starvation resulted in a decline in JH synthesis within 2–3 days and rates of synthesis remained low throughout the experimental period. The growth rate of oöcytes which were not vitellogenic at the time of starvation was depressed whereas the percentage of resorption of vitellogenic oöcytes increased dramatically with starvation. Although the percentage of resorption increased in animals with vitellogenic oöcytes, some mature oöcytes were produced, particularly in animals in which the oöcytes were greater than 5 mm in length at the time of starvation. This suggests that oöcyte maturation can be divided into two distinct phases—an early phase of vitellogenesis associated with high rates of JH synthesis and a late phase, in oöcytes greater than 5 mm, associated with much lower rates of JH synthesis.Stimulation of JH synthesis by farnesenic acid in 5-day starved animals resulted in high rates of JH synthesis, indicating that starvation did not appreciably alter the enzymic activities of the final two stages in JH synthesis. Thus rate limitation did not occur at these stages.Feeding of 5-day starved animals resulted in a transient increase in the rate of JH synthesis. However, rates of JH synthesis and oöcyte growth remained subnormal throughout the observation period, suggesting that the effects of starvation cannot be entirely reversed by feeding. Thus starvation may decrease the reproductive potential of the females.     

Extra-ovariolar egg resorption in a dung beetle, Euoniticellus intermedius

Most oösorption in the dung beetle Euoniticellus intermedius takes place in the haemocoele, oöcytes being extruded from the ovariole before the deposition of the chorion. Oösorption can be induced in the laboratory both by prevention of oviposition and by starvation. For up to two days after the onset of starvation the terminal oöcyte appears normal. After three days the prechorionic oöcyte may move through the ovariole wall; the yolk spheres are then disrupted. On the fourth day little yolk remains in the extruded oöcyte, and most of the extruded cells are degenerating. We suggest that extra-ovariolar egg resorption may be a mechanism for ensuring that the single ovariole is not occluded when conditions are suitable for oviposition.     

Food quality and quantity in relation to egg production in Locusta migratoria migratorioides

Oöcyte development is not initiated when female Locusta migratoria migratorioides are fed on poor, low-protein Agropyron repens. Survival on this diet is improved by the provision of water and small quantities of lush A. repens. When maturing female locusts (with developing oöcytes), previously fed on lush grass, are provided with the poor-quality grass the rate of egg pod production is reduced and terminal oöcyte resorption is increased. The final percentage resorption and the possibility of oviposition is determined by the total quality of food during vitellogenesis. In poor-grass fed locusts the levels of ingestion and utilization are low and suggest that quantitative factors are likely to be critical.Quantitative studies show that the provision of gradually decreasing amounts of A. repens produces corresponding decreases in the rate of egg pod production and increases in terminal oöcyte resorption. When the quantity of food ingested is reduced, the rate of oöcyte development is first reduced, followed at lower levels of feeding by an increase in terminal oöcyte resorption. Ingestion of less than 80 mg (dry weight) of grass/female per day is insufficient to initiate oöcyte development in locusts whose somatic growth period is normal. The significance of these results is discussed.     

The effect of starvation on haemolymph metabolites,fat body and ovarian development in Oxya japonica (Acrididae: Orthoptera)

Haemolymph volume does not change significantly during 96 hr of starvation. Haemolymph and fat body metabolites are depleted significantly in insects denied food for 96 hr. The percentage of oöcyte resorption is increased considerably by starvation. Differences in the utilization of lipid and protein under conditions of starvation between adult Oxya and adult locusts may be attributed to the migratory habit of the latter.     

Determinants of oöcyte degeneration in Drosophila melanogaster

During normal oögenesis in many insects some of the oöcytes fail to mature; instead they degenerate and are resorbed. In this work oöctte degeneration was investigated in Drosophila melanogaster females and found to be limited to early vitellogenic stages (stages 8–10). Even when retained for up to 18 days by females, mature (stage 14) oöcytes showed unaltered protein patterns after separation by SDS polyacrylamide electrophoresis, indicating that protein breakdown, which is characteristic of degeneration, does not occur in chorionated oöcytes.A number of environmental parameters were shown to influence the percentage of degenerating oöcytes in females. Strong responses as reflected by increased stage-8 and 9 oöcyte degeneration were found in females subjected to suboptimal (but not starvation) medium, virgin females, females mechanically unable to oviposit, and females unable to locate suitable oviposition sites. Little or no response was seen in females subjected to crowding, however, since all of these environmental parameters except adult crowding have been shown to decrease fecundity, and therefore the rate of oöcyte production, it is suggested that oöcyte degeneration is a strategy for decreasing the rate of oöcyte production in Drosophila.     

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.     

Rate of follicle growth,change in follicle volume and stages of macromolecular synthesis during ovarian development in Musca domestica

At 21°C the first egg generation takes 6 days to develop. During this period the oöcyte volume increases by a factor of ×5000, and compared with an oögonium the growth factor amounts to ×100,000. The growth rate of the oöcyte increases with each stage of oögenesis, until at stage 5 it reaches 2.5 × 10⁶ μm³/hr. About 35% of the substance stored in the oöcyte originates from the nurse chamber. 30% of the volume is formed in the stage where the oöcyte synthesizes almost exclusively glycogen. Accordingly, about 30% of the volume is provided by the euplasmatic protein synthesis and by the yolk uptake.     

Protein synthesis in the fat body of Leucophaea maderae during vitellogenesis

During the early stages of vitellogenesis in Leucophaea, vitellogenin accounted for most if not all of the secreted protein synthesized by the fat body. Synthesis began about 5 days after mating and continued until 24 hr or so before the formation of the oötheca. Ligation resulted in the degeneration of the oöcytes, the first evidence of which was seen within 24 hr. Ligation also curtailed the synthesis of vitellogenin at about the same time. Isolated abdomens treated with an analog of juvenile hormone commenced vitellogenesis within 12 to 24 hr and measureable oöcyte growth occurred after 5 days. Despite continued synthesis of vitellogenin, the oöcytes in isolated abdomens always degenerated.     

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     

Vitellogenin accumulation in the fat body and haemolymph of Locusta migratoria in relation to egg maturation

Vitellogenins first appear in the fat body of Locusta migratoria during subphase I of vitellogenesis and increase to a constant level during subphase II. A second increase occurs shortly before the oöcyte attains maximal size. Vitellogenin content of fat body subsequently returns to that of subphase I, appropriate to the size of the subterminal oöcyte. The absolute amount of vitellogenin in the fat body is low compared to that found in the haemolymph. Fat body and haemolymph vitellogenins have immunological properties similar to oöcyte yolk proteins—when challenged with oöcyte protein antiserum. They exhibit similar electrophoretic mobility in polyacrylamide gel electrophoresis and are complex glyco-lipoproteins.     

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.     

Phase polymorphism in Schistocerca gregaria: Assessment of juvenile hormone synthesis in relation to vitellogenesis

Juvenile hormone (JH) synthesis by the corpora allata of gregarious and solitarious phase females of Schistocerca gregaria was determined in vitro during the penultimate and last stadia as well as during the first gonotrophic period of adults. Generally, the corpora allata of solitarious females showed higher rates of JH synthetic activity. In addition, in adult females there was a temporal difference between the corpora allata activities of gregarious and solitarious locusts, the latter exhibiting relatively higher rates of JH synthesis early in the first gonotrophic period. The corpus allatum volumes of solitarious females were also generally larger than those of their gregarious counterparts; there was no synchrony between fluctuations in JH synthetic activity and changes in corpus allatum volume in either phase.The early onset of relatively high JH synthetic rates in solitarious females was correlated with the early detection, by rocket immunoelectrophoresis, of vitellogenin in the haemolymph and vitellin in the oöcytes. Vitellogenin appeared in the haemolymph on day 4 in solitarious females and on day 6 in gregarious females and vitellin appeared in the oöcytes on days 6 and 8 respectively. Oöcyte length at which vitellogenesis was first detected was 1.8 mm for gregarious and 1.3 mm for solitarious females. However, despite the accelerated onset of both vitellogenin synthesis and uptake, oöcyte maturation time of solitarious females was longer. In both gregarious and solitarious females, vitellogenin titres increased until oöcytes reached a length of about 4 mm and declined thereafter. Vitellin content of ovaries increased proportionately to oöcyte growth until they attained a length of 5.0 mm. The subsequent increase in length of oöcytes to maturity is attributed to postvitellogenic growth, possibly by hydration.     

Enhancement of juvenile hormone biosynthesis in locusts following electrostimulation of cerebral neurosecretory cells

Electrostimulation of the medial neurosecretory cells of day-1 adult female Locusta migratoria resulted in a significant enhancement of juvenile hormone biosynthesis by the corpora allata within 2–3 days of the operation, as determined by a radiochemical assay for juvenile hormone biosynthesis. This elevation in the rate of juvenile hormone biosynthesis was also reflected in basal oöcyte length, with the oöcytes of stimulated animals significantly larger than the sham-operated animals. Radio-frequency cautery of the cerebral axonal tracts of the medial neurosecretory cells prevented this enhancement in juvenile hormone biosynthesis and in basal oöcyte growth in both stimulated and sham-operated animals.Stimulation of the lateral neurosecretory cells resulted in a slight elevation in rates of juvenile hormone biosynthesis 2 days after the operation. However, after cautery of the medial cell tracts, a significant elevation in juvenile hormone biosynthesis was observed 1 and 2 days after stimulation. Basal oöcyte length in stimulated animals differed significantly from sham-operated animals only on day 6. Cautery of the medial cell tracts again attenuated oöcyte growth. Our results suggest that the medial neurosecretory cells are the source of an allatotropin that can be released by electrostimulation. This substance appears to operate directly on the corpus allatum, causing a change in the juvenile hormone biosynthetic machinery.     

Ovarian maturation in Leucophaea maderae: Juvenile hormone regulation of thymidine uptake into follicle cell DNA

Our research demonstrates that juvenile hormone (JH I) stimulates thymidine incorporation into ovarian follicle cell DNA in the ovoviviparous cockroach, Leucophaea maderae.A rapid, quantitative method for monitoring ³H-thymidine incorporation into ovarian DNA, in vitro, is described. Cultured ovarian tissue from L. maderae incorporates ³H-thymidine into DNA at a linear rate between 16 and 120 min; analysis of the incorporated label revealed at least 98% of it to be in DNA.Using L. maderae females that had been mated 7 days after adult emergence, we monitored the following biochemical phenomena during the 18–22 day period of terminal oöcyte growth: (1) ³H-thymidine incorporation into ovarian DNA: (2) general protein synthesis in fat body; and (3) specific fat body vitellogenin synthesis.Decapitation of mated females with maturing oöcytes arrested both ovarian DNA synthesis and fat body vitellogenin synthesis. Substantial restoration of both types of synthesis was induced by injection of JH I. The resumption of thymidine incorporation into DNA was localized in the follicular epithelium of the terminal oöcyte.In decapitated virgin females, injection of JH I stimulated oöcyte growth and ³H-thymidine incorporation into ovarian DNA. Dose and time response curves indicate that peak stimulation of ovarian DNA synthesis occurred between 72 and 96 hr after administration of a single optimal dose of 25 μg JH I. The concurrent manifestation of ³H-thymidine uptake into ovarian DNA and activity within the fat body indicates that a similar hormonal mode of action may be operative with respect to both tissue types in virgin females.     

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.     

RNA and protein synthesis in the earwig ovary

Cytochemical and autoradiographic studies on the ovaries of Labidura riparia indicate that the oöcyte is supplied with RNA synthesized in the nurse cell nucleus. There is no indication that the oöcyte synthesizes its own RNA. Neither DNA nor protein can be shown to enter the oöcyte from external sources. Although largely cytoplasmic, the incorporation of lysine into protein also localizes in the nucleolus of older oöcytes.     

Experimental evidence for a neuroendocrine control of ecdysone biosynthesis in adult females of Locusta migratoria

The considerable increase in ecdysteroid concentration which occurs in normal Locusta ovaries at the end of each cycle of oöcyte maturation is prevented if the median neurosecretory cells of the pars intercerebralis are cauterized, or if the corpora cardiaca are excised 24 hr before the onset of ecdysone synthesis in normal females. Implantation of additional brain-corpora cardiaca complexes into young vitellogenic females advances the time of ecdysone synthesis by some 12 hr. Oöcyte growth itself is not affected in these different types of experiments.It is inferred from the data of the present study that ecdysone synthesis in the follicle cell epithelium of maturing Locusta ovaries is stimulated by a neurohormone produced in the median neurosecretory cells of the pars intercerebralis and secreted into the blood via the corpora cardiaca.     

Haemolymph ecdysteroid levels in female tsetse fly Glossina fuscipes (Diptera) during the first reproductive cycle: A comparison between virgin and mated females

The fluctuations in haemolymph ecdysteroid levels were recorded by radioimmunoassay during the first two ovarian cycles of the tsetse fly, Glossina fuscipes. During the first ovarian cycle, the patterns of ecdysteroid levels are similar in virgin and mated females. In virgins, the first oöcyte is not ovulated and ecdysteroid levels during the second vitellogenesis remain low. In mated females, vitellogenesis of the second oöcyte is concomitant with growth of the first larva in the mother's uterus and ecdysteroid levels are higher than during the first cycle. Two ecdysteroid increases were recorded in mated females and not in virgins. One coincides with vitellogenesis of the second oöcyte and the other occurs at the end of pregnancy and finishes after larviposition. The roles of ecdysteroids in the regulation of vitellogenesis, ovulation, pregnancy and larviposition are discussed.     

Ultrastructural changes induced by juvenile hormone analogue in oöcyte membranes of apterous4Drosophila melanogaster

Egg chambers from apterous⁴ (ap⁴), a female sterile mutant of Drosophila melanogaster, show none of the microvilli or pinocytotic vesicles which are a prominent feature of the membrane of the wild-type vitellogenic oöcyte. The studies reported here show that a juvenile hormone analogue (ZR515) stimulates formation of microvilli and pinocytotic vesicles in oöcytes of ap⁴ flies. Within 12 hr after topical application of ZR515 to homozygous ap⁴ females the oöcyte membranes exhibit extensive microvilli and pinocytotic activity. The follicle-cell surface adjoining the oöcyte also shows some changes. In vitro studies in which ap⁴ ovaries were incubated in Schneider's Drosophila tissue-culture medium in the presence of ZR515 with or without female haemolymph, or in the absence of ZR515, showed that the analogue acts alone directly on the ovary to cause formation of microvilli and pinocytotic vesicles on the oöcyte membrane.     

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.