Final Stages Of Oogenesis Research Articles

Formation of the diverticular lumen that enables oocyte fertilization in katoikogenic scorpions, Heterometrus spinifer and Opistophthalmus boehmi (Scorpionidae).

The structure of diverticula of the female gonads was analyzed in two scorpions from the family Scorpionidae by means of standard microscopic techniques (light microscopy, histochemistry, transmission electron microscopy). In scorpions, the female gonad, termed the ovariuterus, participates in two consecutive processes: oogenesis and embryogenesis. In sexually reproducing scorpions, the ovariuterus is also involved in fertilization. Both scorpions under study reproduce sexually. They also represent the katoikogenic type of development, which means that oogenesis, fertilization, and embryogenesis take place in the diverticula, which are sac-like outpocketings of the ovariuterine tubules. Formation of a lumen in the diverticulum is indispensable for sperm entry to enable fertilization and subsequent embryogenesis. The aim of the study was to test our hypothesis that the diverticulum lumen forms due to the engagement of the centrally located stalk cells. In this report, we show that in two species of katoikogenic scorpions, at the final stages of oogenesis, the cytoplasm of the stalk cells contains secretory organelles. In the stages preceding fertilization, secretory activity of the stalk cells and fragmentation of their apical parts lead to formation of the diverticulum lumen by a process similar to "cord hollowing" that commonly occurs for lumen formation in other morphogenesis model systems.

Downregulation of homeodomain protein Cut is essential for Drosophila follicle maturation and ovulation.

Proper development and maturation of a follicle is essential for successful ovulation and reproduction; however, the molecular mechanisms for follicle maturation, particularly for somatic follicle cell differentiation, are poorly understood. During Drosophila oogenesis, the somatic follicle cells encasing oocytes undergo two distinct well-established transitions: the mitotic to endocycle switch at stage 6/7 and the endocycle to gene amplification switch at stage10A/10B. Here, we identify a novel third follicle cell transition that occurs in the final stages of oogenesis (stage 13/14). This late follicle cell transition is characterized by upregulation of the transcription factor Hindsight (Hnt), and downregulation of the homeodomain transcription factor Cut and the zinc-finger transcription factor Tramtrack-69 (Ttk69). We demonstrate that inducing expression of Cut in stage 14 follicle cells is sufficient to inhibit follicle rupture and ovulation through its negative regulation of Hnt and promotion of Ttk69 expression. Our work illustrates the importance of the stage13/14 transition for follicle maturation and demonstrates the complex regulation required for somatic follicle cells to differentiate into a state primed for follicle rupture and ovulation.

Co-option of a coordinate system defined by the EGFr and Dpp pathways in the evolution of a morphological novelty

BackgroundMorphological innovation is an elusive and fascinating concept in evolutionary biology. A novel structure may open up an array of possibilities for adaptation, and thus is fundamental to the evolution of complex multicellular life. We use the respiratory appendages on the dorsal-anterior side of the Drosophila eggshell as a model system for morphological novelty. To study the co-option of genetic pathways in the evolution of this novelty we have compared oogenesis and eggshell patterning in Drosophila melanogaster with Ceratitis capitata, a dipteran whose eggs do not bear dorsal appendages.ResultsDuring the final stages of oogenesis, the appendages are formed by specific groups of cells in the follicular epithelium of the egg chamber. These cells are defined via signaling activity of the Dpp and EGFr pathways, and we find that both pathways are active in C. capitata oogenesis. The transcription factor gene mirror is expressed downstream of EGFr activation in a dorsolateral domain in the D. melanogaster egg chamber, but could not be detected during C. capitata oogenesis. In D. melanogaster, mirror regulates the expression of two important genes: broad, which defines the appendage primordia, and pipe, involved in embryonic dorsoventral polarity. In C. capitata, broad remains expressed ubiquitously throughout the follicular epithelium, and is not restricted to the appendage primordia. Interestingly pipe expression did not differ between the two species.ConclusionsOur analysis identifies both broad and mirror as important nodes that have been redeployed in the Drosophila egg chamber patterning network in the evolution of a morphologically novel feature. Further, our results show how pre-existing signals can provide an epithelium with a spatial coordinate system, which can be co-opted for novel patterns.

Microtubule organization and nucleation in the differentiating ovarian follicle of the lizard Podarcis sicula

We analyzed the organization of the microtubular cytoskeleton and the distribution of centrosomes at the different stages of differentiation of the ovarian follicle of the lizard Podarcis sicula by examining immunolabeled α- and γ-tubulins using confocal microscopy. We observed that in the follicular epithelium the differentiation of the nurse pyriform cells is accompanied by a reorganization of the microtubules in the oocyte cortex, changing from a reticular to a radial pattern. Furthermore, these cortical microtubules extend in the cytoplasm of the connected follicle cells through intercellular bridges. Radially oriented microtubules were still more marked in the oocyte cortex during the final stages of oogenesis, when the yolk proteins were incorporated by endocytosis. The nucleation centres of the microtubules (centrosomes) were clearly detectable as γ-tubulin immunolabeled spots in the somatic stromal cells of the germinal bed. A diffuse cytoplasmic immunolabeling together with multiple labeled foci, resembling the desegregation of the centrosomes in early oogenesis of vertebrates and invertebrates, was revealed in the prediplotenic germ cells. In the cytoplasm of growing oocytes, a diffuse labeling of the γ-tubulin antibody was always detectable. In the growing ovarian follicles, immunolabeled spots were detected in the mono-layered follicle cells which surrounded the early oocytes. In follicles with a polymorphic follicular epithelium, only the small follicle cells showed labeled spots. A weak and diffuse labeling was observed in the pyriform cells while in the enlarging intermediate cells the centrosomes degenerated like in the early oocytes. Our observations confirm that in P. sicula most of the oocyte growth is supported by the structural and functional integration of the developing oocyte with the pyriform nurse cells and suggest that their fusion with the oocyte results in an acquirement by these somatic cells of characteristics typical of the germ cells.

Gonochorism and planula brooding in the Mediterranean endemic orange coral Astroides calycularis (Scleractinia: Dendrophylliidae). Morphological aspects of gametogenesis and ontogenesis

Information on reproduction in temperate scleractinian corals is notably scant. Astroides calycularis is an azooxanthellate coral that inhabits the South-Western Mediterranean Sea, in shaded habitats from 0 to 50 m depth. Recently, it has been observed along the coast of the Adriatic Sea. This study is the first in-depth investigation of A. calycularis reproductive biology. Observations from the nineteenth century described A. calycularis as hermaphroditic; in contrast, we demonstrated gonochorism (male and female colonies) and brooding (planula releasing) as the reproductive mode, consistent with other members of the family Dendrophylliidae. Undifferentiated germ cells arose in the gastrodermis and subsequently migrated to the mesoglea, where they completed gametogenesis. During spermatogenesis, spermary diameter increased from 20 to 940 µm. During oogenesis, a conspicuous presence of lipid vesicles of exogenous origin (phagocytes) was observed in the ooplasma. As oogenesis progressed, the synthesis of yolk gradually reduced the nucleus to cytoplasm ratio. In the final stages of oogenesis, the nucleus migrated to the extreme periphery of the oocyte adhering to the oolemma, and became indented. Nuclear migration and shape change may facilitate fertilization and determine the future embryonic axis. During oogenesis, the oocyte diameter increased from 25 to 1590 µm. Embryogenesis took place in the coelenteron. Formation of a blastocoel was not observed, and development proceeded via stereoblastulae with superficial cleavage. Gastrulation took place by delamination. Embryo diameter ranged from 550 to 1140 µm. Released larvae (length 1700 to 2000 µm) were observed in the field during summer, along the benthos.

Desperately seeking embryos (from leftover oocytes)

Desperately seeking embryos (from leftover oocytes)

Expression of bone morphogenetic protein-15 in human oocyte and cumulus granulosa cells primed with recombinant follicle-stimulating hormone followed by human chorionic gonadotropin

Bone morphogenetic protein-15 is expressed in oocytes and cumulus granulosa cells. It may play an important role in the hCG-induced oocyte final maturation and corpus luteum (CL) formation.

Sexual reproduction of the solitary sunset cup coral Leptopsammia pruvoti (Scleractinia: Dendrophylliidae) in the Mediterranean. 1. Morphological aspects of gametogenesis and ontogenesis

Information on the reproduction in scleractinian solitary corals and in those living in temperate zones is notably scant. Leptopsammia pruvoti is a solitary coral living in the Mediterranean Sea and along Atlantic coasts from Portugal to southern England. This coral lives in shaded habitats, from the surface to 70 m in depth, reaching population densities of >17,000 individuals m−2. In this paper, we discuss the morphological aspects of sexual reproduction in this species. In a separate paper, we report the quantitative data on the annual reproductive cycle and make an interspecific comparison of reproductive traits among Dendrophylliidae aimed at defining different reproductive strategies. The present study on L. pruvoti is the first in-depth investigation of the reproductive biology of a species of this genus. As expected for a member of the family Dendrophylliidae, L. pruvoti is a gonochoric and brooding coral. The gastrodermal tissue of the gametogenetic mesenteries we examined was swollen and granular, which led us to hypothesize that interstitial cells could have a trophic function favoring gametogenesis. Undifferentiated germ cells arose in the gastrodermis and subsequently migrated to the mesoglea, where they completed gametogenesis. During spermary development, spermary diameter increased from a minimum of 14 μm during the immature stages to a maximum of 410 μm during the mature stages. As oogenesis progressed, we observed a gradual reduction in the nucleus to cytoplasm ratio due to the steady synthesis of yolk. During the final stages of oogenesis, after having migrated to the extreme periphery of the oocyte and having firmly adhered to the oolemma, the nucleus became indented, assuming a sickle or dome shape. We can hypothesize that the nucleus’ migration and change of shape may have to do with facilitating fertilization and determining the future embryonic axis. During oogenesis, oocyte diameter increased from a minimum of 20 μm during the immature stage to a maximum of 680 μm when mature. Embryogenesis took place in the coelenteron. We did not see any evidence that even hinted at the formation of a blastocoel; embryonic development proceeded via stereoblastulae with superficial cleavage. Gastrulation took place by delamination. Early and late embryos had diameters of 204–724 μm and 290–736 μm, respectively. When released, the larvae had completed ontogenesis and swam by a ciliary movement with the aboral pole at the anterior, their shape varied from spherical to cylindrical (in the latter the oral–aboral axis measured 695–1,595 μm and the transversal one measured 267–633 μm).

Involvement of sex steroids in final stages of oogenesis in Eurasian perch, Perca fluviatilis

Significant plasma 17,20β-dihydroxy-4-pregnen-3-one peaks were measured for the first time in female Eurasian perch, Perca fluviatilis, during the pre-ovulatory period, reaching 3.5 ng ml−1, but was not synchronized with final maturation and ovulation stages.

The ability to generate normal Ca(2+) transients in response to spermatozoa develops during the final stages of oocyte growth and maturation.

Intracellular Ca(2+) oscillations at fertilization are responsible for triggering egg activation. The aim of this study was to examine the effect of the age of the oocyte donor and in-vitro maturation on the generation of Ca(2+) transients at fertilization. The results show that <10% of in-vivo and in-vitro matured oocytes from 19-day old mice develop to the blastocyst stage in vitro. In contrast, 43% of in-vivo and 25% of in-vitro matured oocytes from 24-day old mice developed to the blastocyst stage. In parallel experiments, intracellular Ca(2+) was monitored at fertilization. Oocytes from 19-day old mice generate significantly fewer transients than oocytes from 24-day old mice. In-vitro maturation significantly decreased the ability of oocytes from 19-day old mice but not 24-day old mice to generate Ca(2+) transients in response to spermatozoa. Furthermore, we investigated the effect of oocyte maturation on Ca(2+) signalling. Immature oocytes generated fewer Ca(2+) oscillations and ceased oscillating earlier than mature oocytes. These studies suggest that the ability to generate Ca(2+) transients in response to spermatozoa increases in the final stages of oocyte development and during oocyte maturation. This may contribute to the acquisition of developmental competence in the final stages of oogenesis.

Ontogenesis of the ovary in a moth midge, Tinearia alternata Say (Diptera: Psychodidae).

In a psychodid, Tinearia alternata, the initial differentiation of the polytrophic ovary occurs during the early larval stages. Early in development, each ovary anlage is a solid organ subdivided into three distinct zones: the cortex houses germ cells and somatic interstitial tissue, while two other somatic regions will give rise to the oviduct calyx and anterior part of the lateral oviduct. Germ cell cluster formation precedes the development of ovarioles. Each ovariole houses only one functional egg chamber. All ovarioles within paired ovaries are developmentally synchronized. In the larval ovaries, the newly formed egg chambers and then the ovarioles are intermingeled with and surrounded by the somatic interstitial tissue of the ovary cortex. The interstitial cells give rise to all the somatic elements of the ovarioles. In the pupal ovaries, the remaining interstitial tissue degenerates; thus, the ovarioles protrude into the body cavity. The ovaries in psychodids develop relatively large and swollen oviduct calyxes that are equivalent to receptaculum seminis (spermatheca). The morphological differentiation of germ cells within the egg chambers starts during late larval/early pupal stages. Nurse cell nuclei contain prominent nucleoli and polytene chromosomes. Oocyte growth results from accumulation of yolk and then, in the final stages of oogenesis, from an inflow of cytoplasm from the nurse cells. J. Morphol. 236:167-177, 1998. © 1998 Wiley-Liss, Inc.

Effects of inhibin A and activin A during in vitro maturation of bovine oocytes in hormone- and serum-free medium.

The aim of this study was to investigate whether inhibin A and/or activin A play a role in the acquisition of oocyte competence during the final stages of oogenesis. The particular goal was to establish whether inhibin A and activin A exert development-enhancing effects during in vitro maturation in serum-free media and whether such effects are related to changes in the kinetics of meiotic resumption and/or fertilization rates. Cumulus-oocyte-complexes (COCs) were matured in two control media (Medium 199 [M199] with hormones and serum, hormone-serum control; M199 + 0.6% BSA, BSA-control) and nine treatment media (M199 with 0.6% BSA containing 100, 10, and 1 ng/ml of recombinant human inhibin A, recombinant human activin A, and the combination of the two). Oocytes were fertilized and cultured using standard procedures. Cleavage was assessed at 54 h and blastocyst development at 8 days after in vitro fertilization. Kinetics of oocyte maturation and the fertilization rates were evaluated after fixing and staining (Hoechst 33342) of oocytes at 8, 16, and 22 h after onset of in vitro maturation or of presumptive zygotes at 12 h after in vitro fertilization, respectively. Although there was no effect on cleavage rates, inhibin A and activin A significantly enhanced postcleavage development at concentrations of 10 ng/ml (57.7 +/- 7.5% and 56.6 +/- 11.7%, respectively) and 100 ng/ml (50.6 +/- 18.6% and 56.4 +/- 4.0%, respectively) compared to that in the BSA-control group (24.6 +/- 3.2%). Whereas inhibin A- and activin A-treated oocytes showed development-enhancing effects similar to those in the hormone-serum controls, these groups differed with regard to the kinetics of meiotic resumption. Likewise, the enhanced development of the hormone-serum control and the inhibin A/activin A-treated oocytes was not related to increased fertilization rates relative to the BSA-control. These results suggest that inhibin A and activin A may play important roles during the final stages of oogenesis and that recombinant inhibins and activins are useful compounds for the development of a serum-free culture system for in vitro maturation of oocytes from cattle and possibly other mammalian species.

Morphogenesis of accessory nuclei during final stages of oogenesis in Cosmoconus meridionator (Hymenoptera: Ichneumonidae).

Morphogenesis of accessory nuclei (AN) in chorionated oocytes of Cosmoconus meridionator is described. Initially, each AN contains two dense, morphologically distinct inclusions. During the final stages of postvitellogenesis, these inclusions undergo characteristic transformation that is followed by the extrusion of some substances from AN to the surrounding periplasm. Histo- and cytochemical tests indicate that both inclusions contain RNA, although their precise composition is different. Our results support previous suggestions on the involvement of AN in the distribution of morphogenetic signals.

Ultrastructural study of the sex ratio organism(SRO) transmission into oocytes during oogenesis in Drosophila melanogaster.

The transmission process of Sex Ratio Organisms (SROs) into oocyte during oogenesis in Drosophila melanogaster was studied by electron microscopy. SROs break through a tunica propria, a non-cellular membrane surrounding the egg chamber, and move toward oocytes passing through the intercellular space of the follicle cell layer at previtellogenic stages. After reaching at the surface of an oocyte, they are incorporated into the ooplasm by pinocytosis with progress of vitellogenesis. By the final stages of oogenesis, most SROs become infolded in intracellular vesicles and yolk granules followed by transfer to the interior of the oocyte.

Plasma insulin levels during the spawning migration of the pink salmon, Oncorhynchus gorbuscha

Plasma insulin concentration was measured by homologous radioimmunoassay in male and female pink salmon. Oncorhynchus gorbuscha, during spawning migration in the Fraser and Thompson Rivers, British Columbia. Although the fish ceased feeding prior to entering fresh water, plasma levels of insulin remained stable (males) or even elevated (females) during the final stages of oogenesis and spermatogenesis, decreasing thereafter. Mean concentrations ranged from 0–69 to 1.24 ng ml−1 in males and from 0.33 to 0.88 ng ml−1 in females. At all stages in the anadromous migration where a significant difference in plasma insulin levels between the sexes was observed, males had higher concentrations than females.

Quantification of ribonucleotides and uridine metabolism in ovaries of the kelp fly ( Coelopa frigida, Diptera) during final stages of oogenesis

The concentrations of twelve 5′-ribonucleotides (AMP, ADP, ATP, CMP, CDP, CTP, GMP, GDP, GTP, UMP, UDP, UTP) and four ribonucleotide sugars: CDP-glucose (CDPG), UDP-glucose (UDPG), UDP-N-acetyl-glucosamine (UDPGlcNAc), and UDP-glucoronic acid (UDPGlcUA) in homogenates from Coelopa frigida ovarioles were determined by high pressure liquid chromotography. It was possible to separate the ribonucleotides from each other and from the ribonucleotide sugars in the same analysis. The amount of mono- and di-nucleotides per ovariole remains low during the final stages of oogenesis (stages 10–14). Of the mono-, di- and tri-phosphates the amounts of triphosphates per ovariole are the highest in all cases and double during this phase of follicle development. Of all nucleoside triphosphates, ATP reaches the highest concentration with an increase from 30 pmoles per ovariole to 58 pmoles between stage 10 and 14.

MULTIPLE NUCLEI DURING EARLY OOGENESIS INFLECTONOTUS PYGMAEUSAND OTHER MARSUPIAL FROGS

In the great majority of amphibians yet investigated the occurrence of oocytes with more than one nucleus or more than a single liieiotiC figure is exceptional (Humphries, 1956,1966 ; Parnienter, Derezin andParnienter, 1960 ; Humphrey, 1963) . In the tailed frog Asca/'hus (mel, however, Macgregor and Kezer ( 1970) found that oogenesis regularly involves oocytes with eight nuclei, all but one of @yhich disappear before the final stages of oogenesis. When a related species, Leiopelnta hochstetteri, was investigated by Robinson, Stephenson and Stephenson ( 1973) , onlya single binucleate oocyte wasfoundamong 26oocytes examined. In the present paper the occurrence of niultinucleate stages as a regular feature of oogenesis in several genera of marsupial frogs of South America is reported. The multinucleate condition is associated with the early stages of oogenesis; in large, yolky oocytes only one nucleus is present. Most of the marsupial frogs are inhabitants of the humid forests of South America. In these frogs the aquatic larval stages are reduced or eliminated al together, a phenomenon associated with the fact that the female carries the em bryos on her back, either within a pouch of integument or in shallow depressions of the skin. The genera Flectonotus, Cast rotheca, and Amphignathodon are char acterized by pouches, while in Frit@iana, Crvptobatrachus, Ste fania and Henti phractus the embryos are carried in depressions of the skin. For a list of these frogs with locality and references of taxonomic interest see the work of Duellman (1976). Relatively little information is availal)le regarding reproduction and development in marsupial frogs. The relationship between mother and embryos has been studied in some detail in Gastrotheca riohanzbae, a species that carries the embryos in the potich up to the tadpole stage (see del Pino, Galarza, de Albtija, and Hum phries, 1975, for references). Among the species of Gastrotheca that carry the embryos to the young froglet stage, Gastrotheca ovif era is the best known (see Mertens, 1957, for a description of its life history and references). This report describes some features of oogenesis in 33 species of marsupial frogs that correspond to the described species of Ainphignathodon and Henzi phractus as listed by Duellman (1976), to two (of three) species of Flectonotus, one (of six) species of Stefania and 20 (of 32) species of Gastrotheca. In addi tion, the ovaries of three unnamed species of Gastrotlieca were also analyzed. The peculiarities of oogenesis have been studied in more detail in Flectonotns pvgmaeus, Gastrotheca ovif era and Gastrotheca sp., an unnanied species from Venezuela, since in these instances both living and preserved specimens were available. Living specimens of C. niarsupiata, G. excubitor, C. niertensi and C. plum bea were also

Maternal influence upon the V-type gene position effect in Drosophila melanogaster.

We have studied the influence of various factors on the V-type position effect of the white gene transposed to heterochromatin as a result of different chromosome rearraugements in D. melanogaster. Variegation due to the white gene position effect is much weaker if the flies have received Dp(1;3)wvco from parental males, and not females. The origin of the chromosome rearrangement does not have this influence in the case of T(1;4)wm5 or has it to insignificant extent in the case of In(1)wm4. The Y-chromosome in maternal genome strongly suppresses Dp(1;3)wvco-induced variegation even in the progeny which has not received an extra Y-chromosome but only if this progeny gets Dp(1;3)wvco from the same female. The low temperature (16° C) at which parental females have developed, considerably affects the position effect in the progeny with Dp(1;3)wvco, whereas the temperature of males' development has no influence at all. The maternal temperature effect occurs also when Dp(1;3)wvco has come down from the father, though it is stronger if the mother subjected to low temperature treatment bore the rearrangement. The influence of temperature seems to take effect at the final stages of oogenesis.

Autoradiography ofCoelopa frigida (Diptera) embryos, after labeling with3H-uridine during various phases of oogenesis.

The distribution of tritiated (3H) uridine or its derivatives in embryos of the kelp flyCoelopa frigida is analyzed by autoradiography. The radioactive label is introduced into the growing oocyte, after injectio into females at different time periods post eclosion. The majority of the label remains in the cytoplasm for the entire embryonic development and is presumably incorporated into stable RNA. Only when the precursor is injected toward the final stages of oogenesis, can presence of label be detected in the nuclei, for a short time period during the blastodern stage. Since no preferential location in nucleoli is found, it appears possible that labeled cytidine could have been derived from the original precursor which would be available for incorporation into DNA.

The relationship between oöcyte and follicle in the hen’s ovary as shown by electron microscopy

ABSTRACT In the early stages of oogenesis, the follicle cells contain a ‘complex mass’ of organelles which from its size and position apparently corresponds with the region identified as Golgi body by authors using light microscopy. It contains paired centrioles, radiating tubules, patches of Golgi apparatus and an orderly series of stacks of rough-surfaced endoplasmic reticulum which contain a granular material. It is concluded that these cells are probably secretory. The ‘complex mass’ disappears in the final stages of oogenesis. Using the methyl-green-pyronin test, the follicle cells have been shown to be rich in ribonucleoproteins. Specialized structures termed ‘lining bodies’ are found at irregular intervals at the surfaces of the follicle cells where they abut on to each other or on to the oöcyte. Long processes from the follicle cells indent the surface of the oöcyte, bearing lining bodies with them. Although there is no direct evidence that these lining bodies become engulfed by the oöcyte, nevertheless structures that are found several microns deep within the oöcyte so closely resemble the lining bodies that it seems probable they are derived from them. The available evidence does not support the ideas of Schjeide and his coworkers that the lining bodies give rise to mitochondria. No evidence was found of intercellular bridges between follicle and oöcyte. At first, the follicle and oöcyte membranes lie close together. Gradually, villous-like elevations arise on the oöcyte cell membrane which increase in number and in height. These constitute the zona radiata. Vesicles, containing a granular material, are common in the cortical region of the oöcyte. It is possible that these are formed by pinocytosis, for pinocytoticlike invaginations of the oöcyte cell membrane are visible. These are especially apparent in the zona radiata. The inner layer of the vitelline membrane forms between the follicle and zona radiata, and at first appears to be moulded around projections of the follicle cells. Just before ovulation the cell membrane of the ovum appears to become fragmented into a series of large vacuoles at the cell surface.