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At least 19 recordsLinked to original sources
PubMedDate not supplied

[Morphofunctional changes in the ovarioles of blood-sucking mosquitoes (Diptera, Culicidae) during oogenesis. I. Normal oogenesis].

Contemporary level of knowledge of morphological specificities of the mosquitos' ovariole development during normal oogenesis is analysed basing on the authors' proper research and literature data. Disputable problems of morphofunctional role of certain ovariole structures are discussed. The paper is illustrated by photos and pictures of ovarioles from the moment of germarium formation to the beginning of vitellogenesis.

Animals↗
PubMedDate not supplied

[Morphofunctional changes of the ovarioles of blood-sucking mosquitoes (Diptera, Culicidae) during oogenesis. 2. Abortive oogenesis].

The types of follicle's degeneration of 15 blood-sucking mosquito species were studied. Pregonotrophic degeneration takes place in 1-5 ovarioles immediately after imago hatching before feeding. Agonotrophic degeneration takes place in different number of ovarioles during long periods of sugar feeding. Gonotrophic degeneration takes place in some ovarioles at the same time with normal maturation of eggs in most of ovarioles after blood sucking. In ovarioles the relics are formed as a result of follicles' degeneration only and are named pregonotrophic, agonotrophic, gonotrophic relics, respectively. The possible causes of oosorption at different variants of follicles' degeneration are discussed.

Abortion, Veterinary↗
PubMed1996

The role of nourishment in oogenesis.

Oogenesis in insects is typically a nutrient-limited process, triggered only if sufficient nourishment is available. This nourishment can be acquired during the larval or adult stage, depending on the insect. Timing of food intake will have major effects on mechanisms of hormonal control. When nourishment for eggs is taken primarily by adults, insufficient nutrition inhibits egg development through mechanisms such as inhibition of corpora allata, as seen in Orthoptera and Blattaria. In adult Diptera, lack of protein inhibits release of brain factors that produce reproductive competency or ovarian stimulation. Lepidoptera have been characterized as lacking substantial regulation of oogenesis because egg development is underway at emergence. Many species for which ecological data are available do not mobilize reserves carried over from the larval stage until they feed as adults. The endocrine mechanisms underlying these systems are poorly understood. In many insects, mating and activity can affect nutritional state and therefore oogenesis. Mating can stimulate oogenesis through mobilization of reserves or through nutritional contributions by males to females. Activity, especially flight, and oogenesis can compete for energy. The flight apparatus, especially the muscle, can also compete with oogenesis for protein. Social insects exhibit extreme specializations in oogenesis; females range in fertility from completely sterile to hyperfecund. Food flow within colonies is a major factor regulating fecundity. Finally, maternal nourishment is not needed for oogenesis in parasitoids and pseudoplacental viviparous insects, which produce eggs with little or no yolk. Virtually nothing is known about the endocrine regulation of oogenesis on these insects.

Journal Article↗
PubMed2003

Stage-specific regulation of caspase activity in drosophila oogenesis.

In Drosophila oogenesis, the programmed cell death of germline cells occurs predominantly at three distinct stages. These cell deaths are subject to distinct regulatory controls, as cell death during early and midoogenesis is stress-induced, whereas the cell death of nurse cells in late oogenesis is developmentally regulated. In this report, we show that the effector caspase Drice is activated during cell death in both mid- and late oogenesis, but that the level and localization of activity differ depending on the stage. Active Drice formed localized aggregates during nurse cell death in late oogenesis; however, active Drice was found more ubiquitously and at a higher level during germline cell death in midoogenesis. Because Drice activity was limited in late oogenesis, we examined whether another effector caspase, Dcp-1, could drive the unique morphological events that occur normally in late oogenesis. We found that premature activation of the effector caspase, Dcp-1, resulted in a disappearance of filamentous actin, rather than the formation of actin bundles, suggesting that Dcp-1 activity must also be restrained in late oogenesis. Overexpression of the caspase inhibitor DIAP1 suppressed cell death induced by Dcp-1 but had no effect on cell death during late oogenesis. This limited caspase activation in dying nurse cells may prevent destruction of the nurse cell cytoskeleton and the connected oocyte.

Actins↗
PubMed1991

Female sterile mutations on the second chromosome of Drosophila melanogaster. II. Mutations blocking oogenesis or altering egg morphology.

In mutagenesis screens for recessive female sterile mutations on the second chromosome of Drosophila melanogaster 528 lines were isolated which allow the homozygous females to survive but cause sterility. In 62 of these lines early stages of oogenesis are affected, and these females usually do not lay any eggs. In 333 lines oogenesis proceeds apparently normally to stage 8 of oogenesis, but morphological defects become often apparent during later stages of oogenesis, and are visible in the defective eggs produced by these females whereas 133 lay eggs that appear morphologically normal, but do not support normal embryonic development. Of the lines 341 have been genetically characterized and define a total of 140 loci on the second chromosome. Not all the loci are specific for oogenesis. From the numbers obtained we estimate that the second chromosome of Drosophila contains about 13 loci that are relatively specific for early oogenesis, 70 loci that are specifically required in mid to late oogenesis, and around 30 maternal-effect lethals.

Animals↗
PubMed2006

Mechanisms of programmed cell death during oogenesis in Drosophila virilis.

We describe the features of programmed cell death occurring in the egg chambers of Drosophila virilis during mid-oogenesis and late oogenesis. During mid-oogenesis, the spontaneously degenerating egg chambers exhibit typical characteristics of apoptotic cell death. As revealed by propidium iodide, rhodamine-conjugated phalloidin staining, and the TUNEL assay, respectively, the nurse cells contain condensed chromatin, altered actin cytoskeleton, and fragmented DNA. In vitro caspase activity assays and immunostaining procedures demonstrate that the atretic egg chambers possess high levels of caspase activity. Features of autophagic cell death are also observed during D. virilis mid-oogenesis, as shown by monodansylcadaverine staining, together with an ultrastructural examination by transmission electron microscopy. During the late stages of oogenesis in D. virilis, once again, the two mechanisms, viz., nurse cell cluster apoptosis and autophagy, operate together, manifesting features of cell death similar to those detailed above. Moreover, an altered form of cytochrome c seems to be released from the mitochondria in the nurse cells proximal to the oocyte. We propose that apoptosis and autophagy function synergistically during oogenesis in D. virilis in order to achieve a more efficient elimination of the degenerated nurse cells and abnormal egg chambers.

Actins↗
PubMed1980

Accumulation of individual pA+ RNAs during oogenesis of Xenopus laevis.

RNA metabolism during amphibian oogenesis has been investigated by the analysis of individual cDNA cloned sequences. Two cDNA clone libraries were constructed from the pA+ RNA of Xenopus ovary and of tadpole. The accumulation of RNAs complementary to individual clones was examined during oogenesis by isolating RNA from oocytes of different stages. There are only two patterns of accumulation during oogenesis. Mitochondrial mRNA sequences accumulate throughout all the stages of oogenesis, whereas all other sequences detected cease accumulation early in oogenesis and remain at a constant steady state level for the remainder of oocyte development. In the earliest stages examined, the individual RNAs are already present at approximately 1/4 their final level, and the subsequent increase of all sequences appears to be coordinant. These basic observations were confirmed by colony screening approximately 500 clones. The pattern of RNA accumulation observed is significant, because it had been determined that the total steady state pA+ RNA levels in the oocyte also ceased to increase at the same stage in oogenesis in which each individual sequenced reached a plateau level. In addition, lampbrush chromosomes, which have traditionally been thought to be the site of oocyte pA+ RNA synthesis, are maximally active after the stage in which all pA+ RNAs seem to have reached their final level of accumulation.

Animals↗
PubMed2002

Crossover distribution and high interference for both the X chromosome and an autosome during oogenesis and spermatogenesis in Caenorhabditis elegans.

Regulation of both the number and the location of crossovers during meiosis is important for normal chromosome segregation. We used sequence-tagged site polymorphisms to examine the distribution of all crossovers on the X chromosome during oogenesis and on one autosome during both oogenesis and spermatogenesis in Caenorhabditis elegans. The X chromosome has essentially one crossover during oogenesis, with only three possible double crossover exceptions among 220 recombinant X chromosomes. All three had one of the two crossovers in the same chromosomal interval, suggesting that crossovers in that interval do not cause interference. No other interval was associated with double crossovers. Very high interference was also found on an autosome during oogenesis, implying that each chromosome has only one crossover during oogenesis. During spermatogenesis, recombination on this autosome was reduced by approximately 30% compared to oogenesis, but the relative distribution of the residual crossovers was only slightly different. In contrast to previous results with other autosomes, no double crossover chromosomes were observed. Despite an increased frequency of nonrecombinant chromosomes, segregation of a nonrecombinant autosome during spermatogenesis appears to occur normally. This indicates that an achiasmate segregation system helps to ensure faithful disjunction of autosomes during spermatogenesis.

Animals↗
PubMed1999

Ecdysone response genes govern egg chamber development during mid-oogenesis in Drosophila.

The steroid hormone ecdysone regulates larval development and metamorphosis in Drosophila melanogaster through a complex genetic hierarchy that begins with a small set of early response genes. Here, we present data indicating that the ecdysone response hierarchy also mediates egg chamber maturation during mid-oogenesis. E75, E74 and BR-C are expressed in a stage-specific manner while EcR expression is ubiquitous throughout oogenesis. Decreasing or increasing the ovarian ecdysone titer using a temperature-sensitive mutation or exogenous ecdysone results in corresponding changes in early gene expression. The stage 10 follicle cell expression of E75 in wild-type, K10 and EGF receptor (Egfr) mutant egg chambers reveals regulation of E75 by both the Egfr and ecdysone signaling pathways. Genetic analysis indicates a germline requirement for ecdysone-responsive gene expression. Germline clones of E75 mutations arrest and degenerate during mid-oogenesis and EcR germline clones exhibit a similar phenotype, demonstrating a functional requirement for ecdysone responsiveness during the vitellogenic phase of oogenesis. Finally, the expression of Drosophila Adrenodoxin Reductase increases during mid-oogenesis and clonal analysis confirms that this steroidogenic enzyme is required in the germline for egg chamber development. Together these data suggest that the temporal expression profile of E75, E74 and BR-C may be a functional reflection of ecdysone levels and that ecdysone provides temporal signals regulating the progression of oogenesis and proper specification of dorsal follicle cell fates.

Animals↗
PubMed1979

Origin and spatial distribution of maternal messenger RNA during oogenesis of an insect, Oncopeltus fasciatus.

In order to investigate the origin and spatial distribution of maternal mRNA during oogenesis, in situ hybridization with [3H]-poly(U) was utilized for the detection of poly(A)-containing RNA [poly(A)+RNA] in histological sections of Oncopeltus fasciatus ovaries. In the germarium poly(A)+RNA was found to accumulate in the trophocyte cytoplasm concomitant with the maturation of these cells. Poly(A)+RNA was also detected in the trophic cores and nutritive tubes suggesting that these channels participate in the transport of trophocyte-derived mRNA to the oocytes. Although large amounts of poly(A)+RNA were also detected in the cytoplasm of the follicle cells, particularly during late vitellogenesis when pseudopod-like processes projected into the ooplasm, no evidence was obtained for the transport of poly(A)+RNA from these processes to the oocytes. The content of poly(A)+RNA in the oocyte cytoplasm continually increased during oogenesis. In stage 2--4 oocytes poly(A)+RNA accumulation occurred in the apparent absence of transcriptional activity in the germinal vesicle nuclei suggesting that most maternal mRNA molecules synthesized during early oogenesis are of trophocyte origin. Poly(A)+RNA also continued to accumulate after chorion formation, when the nutritive tubes are longer active in RNA transport. This implies that other sources of maternal mRNA may exist during late oogenesis. The distribution of poly(A)+RNA molecules in the oocyte cytoplasm appeared to be uniform throughout oogenesis with one exception. During late vitellogenesis poly(A)+RNA activity was significantly enhanced in the anterior and posterior periplasmic cytoplasms relative to the lateral periplasm and the endoplasm. After chorion formation these variations disappeared. The results suggest that maternal mRNA molecules arise from at least 2 sources during oogenesis. During late vitellogenesis these molecules appear to be subject to differential localization in the polar perimeters of the oocyte cytoplasm.

Animals↗
PubMed1985

A protein diet initiates oogenesis in Rhodnius prolixus.

Oogenesis in R. prolixus females is induced by feeding blood, blood plasma, a suspension of washed erythrocytes, or 5% solutions of egg albumin, bovine serum albumin or hemoglobin. Unfed females and those fed saline, casein hydrolysate, dextran or sucrose do not initiate oogenesis. The juvenile hormone analogue epoxygeranylgeraniol methyl ester induced oogenesis in unfed females as well as in ethoxyprecocene II-treated insects. The results show that a protein meal was sufficient to initiate oogenesis. They also support the view that oogenesis depends on a relationship between protein ingestion and corpus allatum function and that oogenesis is not controlled by hormones released in response to abdominal stretching.

Animals↗