Transport of ribosomal RNA into the oöcytes of the milkweed bug, Oncopeltus fasciatus

The accumulation of detectable amounts of newly synthesized ribosomes has been shown to be prevented by ligaturing the nutritive cords between the oöcytes and the trophic syncytium of the Oncopeltus ovary. Unligatured control oöcytes on the opposite side of the same bug accumulated normal quantities of newly synthesized ribosomes under the same conditions. It is concluded that the oöcytes are inactive in the synthesis of ribosomes, this function being entirely the province of the trophic syncytium. Evidence is presented which supports the contention that the oöcytes are synthesizing transfer RNA as well as a high molecular weight, polydisperse, fraction which may be the maternal messenger RNA of the egg.     

Yolk deposition in Douglas-fir beetle oöcytes: Possible rôle of RNA synthesis in the follicular epithelium

RNA synthesis and morphological changes in the follicular epithelial cells of oöcytes of Douglas-fir beetle, Dendroctonus pseudotsugae were studied during the reproductive phase. Inhibition of synthesis of DNA dependent RNA by actinomycin D injections blocked yolk deposition in the oöcytes as well as oviposition within the normal period. A mixture of radioactively labelled haemolymph and ovarial proteins was deposited as yolk proteins in the oöcytes of normal beetles. Such proteins were not deposited in the oöcytes of females injected with actinomycin D; the blockage of yolk deposition persisted even when such females were treated extraneously with juvenile hormone.     

Culture in vitro des ovaires de Tenebrio molitor. Hormone juvénile,vitellogenèse,et survie des jeunes ovocytes

In vitro culture of the ovaries of adult Tenebrio molitor is possible on a medium deprived of chick embryo extract. Ovarian and muscular tissue extracts ensure the young oöcytes survival by trophic action. Vitellogenic proteins present in the culture medium enter the oöcytes without the intervention of the corpora allata hormone. Juvenile hormone does not exert a gonadotrophic function in T. molitor.     

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.     

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.     

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.     

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.     

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.     

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.     

Vitellogenic arrest in the cockroach, Blatta orientalis

Starvation stimulated vitellogenic arrest occurs in the cockroach Blatta orientalis after 5 days. This is characterized by cessation of yolk uptake and oöcyte growth.After 5 days of starvation, protein and RNA synthesis decrease, but some macromolecular synthesis continues during the entire starvation period. No oöcyte resorption occurs for up to 15 days of starvation. In contrast to starvation, injection of actinomycin-D results in resorption within 8 hr. The results suggest that B. orientalis copes with starvation by maintaining arrested oöcytes as an alternative to immediate resorption.     

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.     

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).     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

Juvenile hormone-induced vitellogenesis in Apterous4, a non-vitellogenic mutant in Drosophila melanogaster

D. melanogaster females homozygous for the ap⁴ mutant synthesize yolk protein and circulate this protein in the haemolymph at concentrations not different from concentrations found in normal females. However, ap⁴ females deposit little or no yolk protein into developing oöcytes. Topical application of a juvenile hormone analogue (JHA), ZR-515, stimulated sequestration of yolk protein by developing oöcytes of ap⁴ females. JHA had no detectable effects on haemolymph concentrations of yolk protein in either normal or ap⁴ females nor on the protein profiles obtained from electrophoresis of haemolymph samples.