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.     

Oöcyte resorption during ovarian development in the blowfly Lucilia cuprina

Nulliparous females of a normal anautogenous strain of Lucilia cuprina mature all of their primary oöcytes after feeding ad lib on sheep's liver. Females fed measured inadequate amounts of protein-rich materia either fail to mature any oöcytes or mature less than their full complement. These mature oöcytes are smaller than in ad lib fed females. In females maturing no oöcytes, ovarian development ceases with all oöcytes in a pre-vitellogenic or early vitellogenic stage. When females mature only some of their oöcytes, the remainder are resorbed in early vitellogenesis. Few females mature less than 100 oöcytes, if they mature any at all.     

Endocrine control of vitellogenesis in the harlequin bug, Dindymus versicolor

An active corpus allatum is essential for the maturation of eggs in the harlequin bug, Dindymus versicolor. The corpus allatum of virgin females remains virtually inactive and the oöcytes are resorbed once they have grown to the stage at which they become competent to incorporate yolk. Mating provides a stimulus which is essential for the initiation and maintenance of corpus allatum activity and, therefore, vitellogenesis. Corpus allatum activity (and vitellogenesis) can be induced in virgin females either by cutting the allatic nerves or by excision of a certain part of the protocerebrum. It is concluded that the corpus allatum of virgin females is inhibited nervously by the brain and that copulation provides a nervous stimulus which lifts this cerebral inhibition thereby permitting allatum activity.The median neurosecretory cells are not essential for vitellogenesis in Dindymus; however, it is suggested that they are necessary for maximum allatum activity. Evidence is provided to show that the growth and maintenance of the previtellogenic oöcytes are also under the control of the corpus allatum. A mechanism is described whereby the number of vitellogenic oöcytes in the ovarioles is maintained constant.     

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.     

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.     

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.     

Actions of the juvenile hormone, 20-hydroxy-ecdysone,and the oöstatic hormone during oögenesis in the flies Phormia regina and Sarcophaga bullata

Application of juvenile hormone (JH) to sugar-fed Phormia flies leads to full ovarian development, i.e. the flies become autogenous. Application of JH to sugar + liver-fed Phormia leads to the simultaneous development of primary, secondary and tertiary oöcytes, suggesting the role of the oöstatic hormone is to shut off the action of the JH. This is consistent with the notion that the oöstatic hormone may act on the corpus allatum either directly or through the neurosecretory system. Application of 20-hydroxy-ecdysone to Phormia or Sarcophaga, when primary oöcytes have started to develop (stage 4A), causes the primary oöcytes to degenerate, with concomitant development of the secondary oöcytes.     

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.     

Vitellogenic and embryogenic activity of the microtubule disruptor vinblastine following ingestion by the wasp Bracon hebetor

The reproductive performance of Bracon hebetor females was adversely affected by the consumption of sub-lethal doses of vinblastine. While all oögenic cell types present in the gonads at the time of treatment displayed various degrees of fecundity and/or fertility depression, the transitional cells proved to be the least susceptible to vinblastine damage. Vitellogenically active oöcytes were most sensitive to vinblastine. In these oöcytes development was blocked at or prior to the terminal growth phase. Oviposited eggs which did arise from the exposed vitellogenic oöcytes were few in number and characterized by aberrant morphology. Embryogenic effects were predominantlydue to pre-blastoderm formation damage and most pronounced in oöcytes exposed during the most advanced stages of gonadal development, late vitellogenesis through meiotic metaphase I. Reduced egg hatchability also occurred in exposed undifferentiated oögonial cells but the effect was less severe than that seen in the more mature oögenic cells. All observed effects could be accounted for by vinblastine's selective interference with microtubule-dependent processes. Fecundity effects were most closely associated with oöcyte cortex and possibly follicular cell damage which prevented vitellogenic growth beyond the terminal growth phase. Fertility effects were caused by the inhibition of early embryonic karyokinesis with the most plausible target being mitotic spindle formation.     

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.     

The role of factors from the head in the regulation of egg development in the mosquito Aedes aegypti

The relationships between the release of factors from the head after blood-feeding, subsequent levels of ecdysteroids and vitellin, and the ultimate maturation of eggs in Aedes aegypti were investigated. Females were decapitated at various times after a blood meal, at 20 or 48 h after feeding the animals were dissected and divided into two groups, those with arrested oöcytes (yolk length < 100 μm) and those with maturing oöcytes (yolk length > 100 μm). These yolk lengths correspond with the levels of oöcyte growth believed to accompany the proposed initiation and promotion phases of egg development. Animals dissected at 20 h were assayed for ecdysteroid by radioimmunoassay; those dissected at 48 h were assayed for vitellin by rocket immunoelectrophoresis.Non-blood-fed unoperated females contained 8% as much ecdysteroid as blood-fed controls and no measurable vitellin. Females with arrested oöcytes (< 100 μm) were obtained only if decapitations were performed before 8 h; these females had about 20% of the ecdysteroids and 8% of the vitellogenin normally found in blood-fed animals. Females decapitated between 2 and 8 h with maturing oöcytes contained 50–60% as much ecdysteroid and vitellin as blood-fed unoperated controls. Normal ecdysteroid and vitellin levels were reached only when decapitations were delayed for 12 and 24 h, respectively. The number of developing oöcytes was also decreased by early decapitation and was closely correlated with vitellin levels.We conclude that the egg development neurosecretory hormone is released twice, once before 8 h and once after 8 h, to control ecdysteroid levels. We also suggest the presence of other factors from the head that control vitellin levels, the number of developing oöcytes, and the early growth of the oöcyte (initiation).     

Synthesis and deposition of yolk protein in adult Drosophila melanogaster

Newly eclosed Drosophila melanogaster females contain only previtellogenic stage oöcytes and no immunologically detectable female specific haemolymph protein. During the subsequent 48 hr the concentration of female specific protein in the haemolymph rises to a plateau value of 21 μg/μl; at this time yolk protein represents about one third of the total haemolymph protein in adult females. The first mature (stage 14) oöcytes are observed at 48 hr post eclosion. The female specific haemolymph protein and the major protein from mature oöcytes are electophoretically and immunologically the same or very similar. Injection of alpha amanitin into newly eclosed females inhibits the development of mature oöcytes and the degree of inhibition depends on the age of the female at the time of injection. Phenocopies of non-vitellogenic mutants result when alpha amanitin is injected into newly eclosed females; after 36 hr post eclosion no visible inhibition of vitellogenesis (as observed morphologically at 72 hr post eclosion) can be produced by alpha amanitin.     

Influence de modifications des conditions lumineuses sur les rythmes circadiens de vitellogenese et d'ovulation chez Drosophila melanogaster

Under photoperiodic conditions (LD 12:12), a rhythm was observed in the frequencies of ovarian egg chambers and of mature oöcytes. Females reared and kept in permanent darkness (DD) did not show any rhythm. After a transition from LD 12:12 to DD, the rhythm of vitellogenesis remained almost unchanged for at least 5 days while the rhythm of oöcytes retention disappeared.Suppression of a suitable oviposition substrate resulted in an accumulation of mature oöcytes in the ovaries. When a conveneint medium was given again, the egg-laying proved to be highly dependent on the light conditions. Most of the oöcytes remained in retention during the light phase. Significant egg-laying only occurred after the beginning of darkness. In such conditions females can lay one egg every 3 min.The egg-laying rhythm observed under cyclic light conditions thus arises from two separate physiological processes: oöcyte production (vitellogenesis) which has a circadian, endogenous rhythm and oviposition which is directly dependent on the light conditions.     

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.     

Vitellogenin fluctuations in haemolymph and fat body and dynamics of uptake into oöcytes during the reproductive cycle of Diploptera punctata

Haemolymph and fat body soluble protein titres have been examined during the reproductive cycle of Diploptera punctata, with particular emphasis on the occurrence of vitellogenin and its uptake into the developing oöcytes. Vitellogenin was first detected in the haemolymph of mated females 2 days after adult eclosion at about the same time that vitellin deposition in basal oöcytes began. Peak haemolymph titres of vitellogenin occurred on day 6, correlated with the completion of yolk uptake. Thereafter vitellogenin levels declined and were generally undetectable throughout most of gestation, rising again shortly before parturition in association with the second gonotrophic cycle. Total haemolymph protein levels were not correlated with vitellogenesis.Soluble fat body vitellogenin titres of mated females remained low during the first oöcyte growth period but then rose several-fold at its completion and remained high throughout pregnancy and the second gonotrophic cycle. Total fat body soluble proteins decline after adult eclosion in association with oöcyte growth.Vitellin accumulation in basal oöcytes was related linearly to increase in volume until the onset of chorion formation. Thus no post-vitellogenic growth period was detected.     

Lipid accumulation in oöcytes of Locusta migratoria migratorioides

Oöcytes of Locusta migratoria accumulate lipids during vitellogenesis by acylation of haemolymph diacylglyerols and by de novo synthesis from free fatty acids and glycerol. This was shown by following the incorporation of lipids in vivo after injecting (1-¹⁴C)-palmitate to vitellogenic females and in vitro by incubation of isolated oöcytes with (1-¹⁴C)-palmitate, (1,3-¹⁴C)-glycerol and (¹⁴C)-labelled male and female haemolymph. Both the lipid and protein components of diacylglycerol carrier protein were taken up by isolated locust oöcytes incubated in vitro.Triacylglycerols were preferentially synthesized in vitro by isolated oöcytes incubated in the presence of labelled haemolymph, while phospholipids were the major component synthesized by incubating with (1-¹⁴C)-palmitate.     

Evidence for haemoglobin uptake by oöcytes of Chironomus thummi

Developing oöcytes of a haemoglobin-containing fly, Chironomus thummi, have been investigated using the 3,3′-diaminobenzidine method for their endogeneous peroxidase activity. In the previtellogenic oöcytes the reaction product, which is thought due to the peroxidatic activity of the haemoglobins, is not observed within the oöcytes. Vitellogenic oöcytes appear active in the uptake and incorporation of the externally derived peroxidese-active material into the yolk. The reaction product which is first visualized in the extracellular spaces within the follicle, then the pinosomes and multivesicular bodies of the oöcyte, is later seen in the mature yolk granules. These observations are discussed in terms of their relation to the accumulation of haemoglobin as a part of the yolk.     

Ovarian dynamics in Heliconius butterflies: Correlations among daily oviposition rates,egg weights,and quantitative aspects of oögenesis

Both oviposition and ovarian morphology were studied in individual butterflies of the neotropical genus Heliconius, which as adults ingest amino acids from pollen, live up to 6 months, and have continuous oögenesis. Among female Heliconius charitonius, daily oviposition correlates directly with the total number of oöcytes developing in the ovaries. The calculated time required for complete growth of one oöcyte is, however, reasonably constant among individuals of a species with widely varying oviposition rates. Thus, within a species, butterflies laying more eggs per day are not necessarily maturing each at a faster rate, but are processing more oöcytes simultaneously in their ovaries. A further correlation between oviposition rate and adult size suggests that in H. charitonius both ovarian capacity and daily egg production are determined ultimately by extent and/or quality of larval nutrition. Among other Heliconius species, those producing larger eggs generally take longer to make them, but also may develop more oöcytes at the same time in their ovaries. Finally, maximal volume attained by the cap of seven nurse cells associated with each growing oöcyte appears constant within a species and among species is directly proportional to average mature egg weight.     

Endocrine control of oögenesis in the housefly,Musca domestica vicina

The endocrine system involved in the control of oögenesis in the housefly, Musca domestica vicina, was investigated. Allatectomy, decapitation, and starvation of newly emerged females resulted in inhibition of oögenesis, showing a close relationship between enlargement of the corpus allatum and growth of follicles during the first oögenesis. Histological observation of sexually matured females showed active secretion of the corpus allatum and the medial neurosecretory cells of pars intercerebralis. Topical application of juvenile hormone analogues (JHA) to the allatectomized fly induced the growth of ovary, and critical doses of methoprene and methyl-7, 11-diethyl-juvenate for the maturation of the ovary were determined. JHA stimulated initiationof oögenesis in the starved or decapitated flies as well as vitellogenesis in the sugar-fed one; subsequently it was found that juvenile hormone acted not only as a gonadotropin but also as a regulator of vitellogenesis. Furthermore, JHA stimulated cell lysis in pupal fat body of female flies, indicating a possible influence of juvenile hormone upon the process of releasing vitellogenin.     

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.