Muco-follicle cells of the jelly coat in the oocyte envelope of the sheatfish (Silurus glanis L.)

During early vitellogenesis of the oocytes of Silurus glanis, the follicular cells proliferate, their epithelial organization becomes disrupted, and they transform into an irregularly structured large mass of cells engaged in intensive secretory activity. They contain nuclei, rough endoplasmic reticulum, Golgi bodies, and secretory inclusions termed “acorn bodies,” which are synthesized in the cytoplasm. The acorn bodies have two components: an electron-dense cap and a moderately electron-dense body. As development proceeds, the acorn bodies become modified into spherules of mucous material, the mucosomes. The electron-dense part persists as a small calotte or crescent often irregularly structured at the periphery of the mucosome, and fragments of it are dispersed into the interior of the mucosomal body. The mucosomes are membrane-bound and contain small granules, 55 nm in diameter. At the end of vitellogenesis, the follicle cells are filled with mucosomes, and cytoplasmic residua can only sparingly be observed among them. Oocytic microvilli extend through the zona radiata and intermingle with follicular cell processes in the cleft between the zona radiata and the belt of mucosomes during growth of the oocyte. Capillaries develop in connective tissue of the theca layer as vitellogenesis proceeds. © 1993 Wiley-Liss, Inc.     

Fine Structure of the Ovarian Development in the Orb-web Spider, Nephila clavata

ABSTRACT Fine structural changes of the ovary and cellular composition of oocyte with respect to ovarian development in the orb-web spider, Nephila clavata were examined by scanning and transmission electron microscopy. Unlike the other arthropods, the ovary of this spider has only two kinds of cells-follicle cells and oocytes. During the ovarian maturation, each oocyte bulges into the body cavity and attaches to surface of the elongated ovarian epithelium through its peculiar short stalk attachments. In the cytoplasm of the developing oocyte two main types of yolk granules, electron-dense proteid yolk and electron-lucent lipid yolk granules, are compactly aggregated with numerous glycogen particles. The cytoplasm of the developing oocyte contains a lot of ribosomes, poorly developed rough endoplasmic reticulum, mitochondria and lipid droplets. These cell organelles, however, gradually degenerate by the later stage of vitellogenesis. During the active vitellogenesis stage, the proteid yolk is very rapidly formed and the oocyte increases in size. However, the micropinocytosis invagination or pinocytotic vesicles can scarcely be recognized, although the microvilli can be found in some space between the oocyte and ovarian epithelium. During the vitellogenesis, the lipid droplets in the cytoplasm of oocytes increase in number, and become abundant in the peripheral cytoplasm close to the stalks. On completion of the yolk formation the vitelline membrane, which is composed of an inner homogeneous electron-lucent component and an outer layer of electron-dense component is formed around the oocyte.     

Ultrastructural investigations of the ovary and oogenesis in the pycnogonids Cilunculus armatus and Ammothella biunguiculata (Pycnogonida, Ammotheidae)

Abstract. Ovarian ultrastructure and oogenesis in two pycnogonid species, Cilunculus armatus and Ammothella biunguiculata , were investigated. The ovary is morphologically and functionally divided into trunk and pedal parts. The former represents the germarium and contains very young germ cells in a pachytene or postpachytene phase, whereas the latter houses developing previtellogenic and vitellogenic oocytes and represents the vitellarium. Intercellular bridges were occasionally found between young (trunk) germ cells. This indicates that in pycnogonids, as in other animal groups, at the onset of oogenesis clusters of germ cells are generated. As nurse cells are absent in the ovaries of investigated species, the clusters must secondarily split into individual oocytes. In the vitellarium, the oocytes are located outside the ovary. Each oocyte is connected to the ovarian tissue by a stalk composed of several somatic cells. The stalk cells directly associated with the oocyte are equipped with irregular projections that reach the oocyte plasma membrane. This observation suggests that the stalk cells may play a nutritive role. The ooplasm of vitellogenic oocytes comprises mitochondria, free ribosomes, stacks of annulate lamellae, active Golgi complexes, and vesicles derived from these complexes. Within the latter, numerous electron-dense bodies are present. We suggest that these bodies contribute to yolk formation.     

泥螺卵黄发生过程中线粒体的变化

利用透射电镜（TEM）技术研究了泥螺卵黄发生过程中线粒体的形态结构的变化特点,结果表明,从卵黄发生早期到晚期,卵母细胞内线粒体经历了从外部形态到内部结构的一系列变化。卵黄合成初期的卵母细胞内,线粒体多,结构典型,仅部分线粒体外膜破裂,嵴 和内膜逐渐消失,卵黄发生中期,线粒体基质空泡化,嵴和内膜消失,腔内充满颗粒状物质,最后演变成卵黄颗粒,随着卵母细胞的发育,卵黄颗粒的数量和直径逐渐增加,卵黄发生后期,卵质中胞器不发达,细胞质中充满卵黄颗粒,在卵黄颗粒之间仅有少量线粒体存在,提供细胞代谢所需的能量,此外,对线粒体在卵黄形成中的功能,去向及行为变化等 进行了讨论。     

Large P body-like RNPs form in C. elegans oocytes in response to arrested ovulation, heat shock, osmotic stress, and anoxia and are regulated by the major sperm protein pathway

As Caenorhabditis elegans hermaphrodites age, sperm become depleted, ovulation arrests, and oocytes accumulate in the gonad arm. Large ribonucleoprotein (RNP) foci form in these arrested oocytes that contain RNA-binding proteins and translationally masked maternal mRNAs. Within 65 min of mating, the RNP foci dissociate and fertilization proceeds. The majority of arrested oocytes with foci result in viable embryos upon fertilization, suggesting that foci are not deleterious to oocyte function. We have determined that foci formation is not strictly a function of aging, and the somatic, ceh-18, branch of the major sperm protein pathway regulates the formation and dissociation of oocyte foci. Our hypothesis for the function of oocyte RNP foci is similar to the RNA-related functions of processing bodies (P bodies) and stress granules; here, we show three orthologs of P body proteins, DCP-2, CAR-1 and CGH-1, and two markers of stress granules, poly (A) binding protein (PABP) and TIA-1, appear to be present in the oocyte RNP foci. Our results are the first in vivo demonstration linking components of P bodies and stress granules in the germ line of a metazoan. Furthermore, our data demonstrate that formation of oocyte RNP foci is inducible in non-arrested oocytes by heat shock, osmotic stress, or anoxia, similar to the induction of stress granules in mammalian cells and P bodies in yeast. These data suggest commonalities between oocytes undergoing delayed fertilization and cells that are stressed environmentally, as to how they modulate mRNAs and regulate translation.     

Differentiation and distribution of annulate lamellae in growing oocytes in the newt, Cynops pyrrhogaster

Stages of oocyte development in Cynops pyrrogaster are defined, and changes of annulate lamellae in their fine structure, number, sizes and locations during oogenesis are described. The results show that two different types of annulate lamellae occur during oogenesis. One type differentiates in or at the periphery of vesicle-rich cytoplasm at the early stages of vitellogenesis and increases in number and size. The maximum number of about 40 stacks per median section of oocyte is reached at the stage of complete differentiation of the animal and the vegetal hemispheres. In these growing oocytes, all the stacks show elongate appearances and tetragonal arrangements of annuli as common characteristics. A second type of stacks of annulate lamellae is added anew in full-grown oocytes, increasing the number of stacks per median section of the oocyte to about 90. The new stacks occur in close contact with electron-dense bodies in the cytoplasm and have a massive appearance and hexagonal array of annuli. It is suggested that they appear coincidentally with the onset of oocyte maturation. The possible significance of the observed results is discussed.     

The role of the fat body, midgut and ovary in vitellogenin production and vitellogenesis in the female tick, Dermacentor variabilis.

Polyclonal antibodies directed against D. variabilis vitellin were utilized for immunocytochemistry at the ultrastructural level. We localized vitellogenin (Vg) in rough endoplasmic reticulum cisternae, secretory granules and secreted products of fat body trophocytes and midgut vitellogenic cells from feeding and ovipositing females. Vg was localized in the oocyte Golgi bodies and in the yolk bodies of both feeding and ovipositing females. Uptake of exogenous Vg was indicated by the presence of immunospecific gold probe in coated pits and coated vesicles at the apical plasma membrane of oocytes from females in rapid engorgement and oviposition. In unmated females little detectable evidence of Vg uptake by developing oocytes suggests that mating and host detachment signal the beginning of vitellogenesis. We conclude that fat body trophocytes, midgut vitellogenic cells and oocytes are involved in the synthesis and/or processing of Vg and that feeding is the signal associated with the initiation of Vg synthesis and/or processing.     

Cytodifferentiation and vitellogenesis during oogenesis in arachnida: Cytological studies on developing oocytes of a harvestman

Light and electron microscope studies were made on harvestman oocytes during the course of their origin, differentiation, and vitellogenesis. The germ cells appear to originate from the ovarian epithelium. They subsequently migrate to the outer surface of the epithelium, where they remain attached often by means of stalk cells which suspend them in the hemocoel during oogenesis. The “Balbiani bodies,” “yolk nuclei,” or “nuage” constitute a prominent feature of young, previtellogenic oocytes, and take the form of large, but variable sizes of electron-dense cytoplasmic aggregates with small fibrogranular components. The cytoplasmic aggregates fragment and disperse, and cannot be detected in vitellogenic oocytes. The young oocytes become surrounded by a vitelline envelope that appears to represent a secretory product of the oocyte. The previtellogenic oocytes are impermeable to horseradish peroxidase under both in vivo and in vitro conditions. In addition to mitochondria, dictyosomes, and abundant ribosomes, the ooplasm of the previtellogenic oocyte acquires both vesicular and lamellar forms of the rough-surfaced endoplasmic reticulum. In many areas, a dense homogeneous product appears within the cisternae of the endoplasmic reticulum and represents nascent yolk protein synthesized by the oocyte during early stages of vitellogenesis. Later in vitellogenesis, the oocyte becomes permeable to horseradish peroxidase under both in vivo and in vitro conditions. This change is associated with a massive process of micropinocytosis which is reflected in the presence of large numbers of vesicles of variable form and structure in the cortical ooplasm. Both spherical and tubular vesicles are present, as are coated and uncoated vesicles. Stages in the fusion of the vesicles with each other and with developing yolk platelets are illustrated. In the harvester oocytes, vitellogenesis is a process that involves both autosynthetic and heterosynthetic mechanisms.     

Oogenesis in the leech Glossiphonia heteroclita (Annelida, Hirudinea, Glossiphoniidae) II. Vitellogenesis, follicle cell structure and egg shell formation

By the end of previtellogenesis, the oocytes of Glossiphonia heteroclita gradually protrude into the ovary cavity. As a result they lose contact with the ovary cord (which begins to degenerate) and float freely within the hemocoelomic fluid. The oocyte's ooplasm is rich in numerous well-developed Golgi complexes showing high secretory activity, normal and transforming mitochondria, cisternae of rER and vast amounts of ribosomes. The transforming mitochondria become small lipid droplets as vitellogenesis progresses. The oolemma forms microvilli, numerous coated pits and vesicles occur at the base of the microvilli, and the first yolk spheres appear in the peripheral ooplasm. A mixed mechanism of vitellogenesis is suggested. The eggs are covered by a thin vitelline envelope with microvilli projecting through it. The envelope is formed by the oocyte. The vitelline envelope is produced by exocytosis of vesicles containing two kinds of material, one of which is electron-dense and seems not to participate in envelope formation. The cortical ooplasm of fully grown oocytes contains many cytoskeletal elements (F-actin) and numerous membrane-bound vesicles filled with stratified content. Those vesicles probably are cortical granules. The follicle cells surrounding growing oocytes have the following features: (1) they do not lie on a basal lamina; (2) their plasma membrane folds deeply, forming invaginations which eventually seem to form channels throughout their cytoplasm; (3) the plasma membrane facing the ovary lumen is lined with a layer of dense material; and (4) the plasma membrane facing the oocyte forms thin projections which intermingle with the oocyte microvilli. In late oogenesis, the follicle cells detach from the oocytes and degenerate in the ovary lumen.     

The dynamics of yolk deposition in the desert locust Schistocerca gregaria

Injection of the protein dye Fast Green or the fluid-phase probe fluorescein dextran into the haemolymph of vitellogenic female desert locusts (Schistocerca gregaria) resulted in their incorporation into oocytes. We used Fast Green to study the physical dynamics of yolk deposition during vitellogenesis. Timed maternal injections of Fast Green reveal that yolk deposition and oocyte growth are inextricably linked during vitellogenesis, and that little or no yolk movement occurs within oocytes prior to embryogenesis. The yolk granules laid down early during vitellogenesis lie at the centre of the egg, with yolk granules deposited later packed around these, such that they lie progressively closer to the eventual egg surface. In contrast, during early embryogenesis yolk granules migrate in a manner that closely resembles the movement of early cleavage nuclei. We find fluorescein dextran to be a clear, robust and developmentally inert marker for the timing of maternal injections relative to vitellogenesis in S. gregaria, and we propose its use in parental RNAi or morpholino knockdown experiments. With such experiments in mind, we show that fluorescein-labelled DNA oligonucleotides are internalized within oocytes during vitellogenesis. However, neither Fast Green, fluorescein dextran nor fluorescein-labelled DNA oligonucleotides are detectably transferred from yolk granules to embryonic cells during embryogenesis, and our initial attempts at parental RNAi using maternal injections of dsRNA targeted to late vitellogenesis have proved unsuccessful.     

Oogenesls in the terrestrial hermit crab,coenobita clypeatus (decapoda,anomura): II. Vitellogenesis

Oocytes from the land hermit crab, Coenobita clypeatus, in various stages of vitellogenesis were examined by light and electron microscopy. Early vitellogenic oocytes are characterized by accumulations of discrete vesicles of endoplasmic reticulum in the perinuclear cytoplasm. As oocytes develop, the endoplasmic reticulum becomes abundant, and numerous Golgi complexes are seen. There is a well developed Golgi-endoplasmic reticulum interaction. Within the confines of the reticulum are discrete intracisternal granules, which can be seen coalescing into electron-dense yolk bodies. Lipid accumulation is seen throughout the cytoplasm. Coincident with the burst of intra-oocytic metabolism are oolemma modifications and micropinocytosis, which provide ultrastructural evidence for extra-oocytic yolk production. The mature oocyte contains numerous yolk and lipid vesicles of varying electron density that comprise both intra- and extra-oocytic substrates.     

Developmental studies of vitellogenesis in a dipteran insect, Chironomus thummi.

Vitellogenesis of developing oocytes of a Dipteran insect Chironomus thummi has been investigated. The onset of yolk deposition is marked by the differentiation of the oolemma including the formation of microvilli and endocytosis. These changes are accompanied by the appearance of small electron dense granules, similar in density to the yolk platelets, arising through the sequential accumulation of material into the matrices of the multivesicular bodies (MVBs). These latter structures are produced in the previtellogenic oocytes of the pharate pupae and early pharate adults. Often the limiting membrane of the MVBs bears bristle coats resembling those of the coated vesicles of pinocytotic origin, suggesting that it is through the fusion with the pinocytotic vesicles that the accumulation of dense material in the MVBs results. That the Mvbs transform into structures resembling yolk granules is supported by statistical analysis which indicates that the decrease in the number of electron-dense MVBs coincides with the increase in the occurrence of small dense yolk granules. In the late pharate adult stage the yolk granules are considerably larger than those of earlier stages. It is during this period that at least one type of electron-dense granule occurs at the oocyte follicle cell border, and that these apparently contribute to the formation of the vitelline envelope. The results of the present study indicate that preformed oocytic elements, the MVBs, play a strategic role in the formation and arrangement of the yolk granules in Chironomus. Since these structures account for the bulk of the ooplasm, it appears that the MVBs are at least partly responsible for the correct ordering of the cytoplasmic constituents of the oocytes, which is critical for the proper development and differentiation of the embryo.     

Is there a germ plasm in mouse oocytes?

It was found that in the Graafian oocytes of laboratory mice Mus musculus the population of electron-dense bodies contains two patterns of structures. One of these, designated as cortical granules, originated from the Golgi complex and was surrounded by a membrane. The other was discovered as cristae-containing mitochondrial derivatives lacked an outer membrane. It was found that the mitochondrial derivatives underwent progressive condensation and transformed into electron-dense bodies similar to germinal bodies of metazoan animals. Based on examination of Graafian follicle oocytes from 5 female individuals, about 15% of electron-dense bodies were cortical granules. However, about 85% of electron-dense bodies were condensing mitochondrial derivatives transforming into electron-dense bodies.     

Formation of the karyosome in developing oocytes of weevils (Coleoptera, Curculionidae)

A complex structure termed the karyosome forms in the nuclei of the developing oocytes of Anthonomus pomorum, Hylobius abietis and Phyllobius sp. (Coleoptera: Curculionidae). It is composed of highly condensed chromosomes, fused with an electron-dense granular material. There are two types of nuclear body associated with the karyosome. The smaller bodies are found in the immediate vicinity of the karyosome. The larger, and more electron-dense, bodies originate next to the condensing chromosomes. During vitellogenesis, the latter bodies disperse in the karyoplasm, and at least some of them locate in the characteristic irregular projections of the germinal vesicle. Morphologically, these projections resemble the accessory nuclei described in other insects. In the studied species, a proteinaceous sheath, the so-called karyosome capsule, surrounds the karyosome. The formation of the karyosome and its capsule occurs during previtellogenesis, so that these structures are fully formed at the onset of vitellogenesis. An extraction of the oocyte cytoplasm with Triton X-100 showed that the material constituting the karyosome capsule is filamentous. Staining with rhodamine-conjugated phalloidin reveals large amount of F-actin in the karyosome capsule.     

The structure of symplasmic early oocytes and their enveloping sheath cells in the polychaete,Platynereis dumerilii

1. Early oocytes of Platynereis dumerilii are found in clusters floating in the coelom. The oocytes of a cluster form a syncytium which is enveloped by several sheath cells. 2. At stage 2, only a single sheath cell per cluster remains, and it penetrates the group of rounded oocytes, enveloping each one of them. At stage 4, this cell contains a reticular basket made up of bundles of filaments and is inferred to be degenerating, from the presence of vacuoles, clumps of pigment-like material, and atypical mitochondria. 3. Synaptonemal complexes are typical of the nuclei of stage 2 oocytes. Oocytes of stage 4 (early vitellogenesis) contain stacks of endoplasmic reticulum in a distinctive arrangement, with interspersed electron-dense masses. Similar masses accumulate in the cytoplasm close to the nucleus and adjacent to the nuclear pores. 4. From the present observations, a physical supporting rather than a nutritive function is attributed to the sheath cell, which ensures cohesion among the oocytes connected with each other throughout the cluster phase by cytoplasmic bridges. This finding is discussed with respect to conclusions drawn from oocyte transplantation experiments.     

东方扁虾卵子发生的超微结构

根据卵细胞的形态、内部结构特征及卵母细胞与滤泡细胞之间的关系,东方扁虾的卵子发生可划分为卵原细胞、卵黄发生前卵母细胞、卵黄发生卵母细胞和成熟卵母细胞等四个时期。卵原细胞胞质稀少,胞器以滑面内质网为主。卵黄发生前卵母细胞核明显膨大,特称为生发泡;在靠近核外膜的胞质中可观察到核仁外排物。卵黄发生卵母细胞逐渐为滤泡细胞所包围;卵黄合成旺盛,胞质中因而形成并积累了越来越多的卵黄粒。东方扁虾卵母细胞的卵黄发生是二源的。游离型核糖体率先参与内源性卵黄合成形成无膜卵黄粒。粗面内质网是内源性卵黄形成的主要胞器。滑面内质网、线粒体和溶酶体以多种方式活跃地参与卵黄粒形成。卵周隙内的外源性物质有两个来源:滤泡细胞的合成产物和血淋巴携带、转运的卵黄蛋白前体物。这些外源性物质主要通过质膜的微吞饮作用和微绒毛的吸收作用这两种方式进入卵母细胞,进而形成外源性卵黄。内源性和外源性的卵黄物质共同参与成熟卵母细胞中富含髓样小体的卵黄粒的形成。卵壳的形成和微绒毛的回缩被认为是东方扁虾卵母细胞成熟的形态学标志。       

Oogenesis in Campodea sp. (Insecta,Diplura): Chorion formation and the ultrastructure of follicle cells

During advanced vitellogenesis the follicle cells of Campodea sp. are well developed and contain numerous electron-dense secretory vacuoles. In the postvitellogenic phase the contents of these vacuoles are released from follicle cells and give rise to a thin chorion on the oocyte surface. Concurrently, segregation of yolk spheres takes place in the ooplasm: small spheres migrate to the oocyte periphery and come to lie in the so-called peripheral zone of cytoplasm, whereas large spheres remain in the cell centre.     

泥螺卵子发生的超微结构研究

利用透射电镜观察了泥螺卵子发生过程。结果表明 ,泥螺的卵子发生可划分为卵原细胞、卵黄发生早期、卵黄发生中期及卵黄发生后期卵母细胞 4个时期。卵原细胞核大而圆 ,胞质内分布有少量的线粒体和高尔基囊泡 ,细胞表面具微绒毛。卵黄发生早期的卵母细胞 ,胞质中各类细胞器发达 ,并出现数量较多的类朦胧子。卵黄发生中期的卵母细胞胞体迅速增大 ,核伸出伪足状突起 ,卵质中各种细胞器活动活跃 ,并参与形成卵黄粒和脂滴。此期还可观察到卵母细胞与滤泡细胞间的物质交换现象。卵黄发生后期的卵母细胞体积增至最大 ,细胞器数量减少。本文就卵黄发生前后卵母细胞内部构造的变化、意义及滤泡细胞与卵母细胞蛋白来源间的关系作了探讨     

Histological and histochemical study of female germ cell development in the dusky grouper Epinephelus marginatus (Lowe, 1834)

The developmental stages of female germ cells were analysed in a wild population of the protogynous teleost Epinephelus marginatus (Lowe, 1834). 321 wild dusky grouper females were collected in the South Mediterranean Sea during the spawning season and their ovaries analysed using histological and histochemical techniques. Oocyte morphology, nucleus-cytoplasm ratio (N/C) range, location and movements of cytoplasmic inclusions during primary growth, vitellogenesis and final oocyte maturation were described. The distribution of proteins, lipids and carbohydrates through oocyte development was also investigated in 50 females. Lipid vesicles appeared firstly in the mid ooplasm of oocytes larger than 130 microm, at the beginning of the secondary growth phase. Immediately afterwards, small carbohydrate granules (PAS and Alcian blue positive) appeared before the occurrence of the first yolk granules. Tyrosine-enriched proteins were especially evidenced in the zona radiata interna of late vitellogenic oocytes. Specific lectin binding patterns reflected characteristic differences in the content and distribution of specific sugar moieties expressed in the oocytes during vitellogenesis and final maturation. At the end of vitellogenesis and during final maturation, follicular cells, zona radiata, and cortical alveoli were characterised by a strong increase of specific binding for WGA.     

Cytochemical and ultrastructural study of oocyte development of the crab Eriocheir sinensis. II. Oogenesis after removal of the eyestalk]

The effect produced by an eyestalk removal have been studied on Eriocheir females at different physiological stages. In juvenile and prepuberal crabs, the operation induces an important rise of the oocyte diameter. Only a few variations are observed in puberal females oocytes. Cytological changes are found at first at the nucleolar level. The granular area increases and the nucleolar vacuoles volume decreases. Then the granules (precursor material to endogenous yolk) disappear in the reticulum cisternae. At this time, the endogenous yolk seems essentially elaborated within yolk lobules. The envelope of these lobules is enhanced by ribosomes. In juvenile females (oocytes initially in previtellogenesis) exogenous yolk does not appear. Nevertheless in prepuberal females, following eyestalks deprivation, the oocytes, initially at the endogenous vitellogenesis stage, quickly reach the vitellogenesis second stage. In such oocytes, the microvilli development and pinocytose vesicles number are greater than normally. Cytochemical tests reactions do not demonstrate differences in the yolk material (endogenous and exogenous) nature from experimented oocytes and controls. In juvenile and prepuberal oocytes, the multivesicular bodies and lysosomes proliferation, the increase in glycogen and lipids amount express a metabolic disturbance resulting from an acceleration of growth processes. However in eyestalk-less prepuberal females no difference with the control oocytes was noticed.