Development of the follicle complex and oocyte staging in red drum,sciaenops ocellatus linnaeus, 1776 (perciformes,sciaenidae)

Pelagic egg development in red drum, Sciaenops ocellatus, is described using tiered staging. Based on mitosis and meiosis, there are five periods: Mitosis of Oogonia, Active Meiosis I, Arrested Meiosis I, Active Meiosis II, and Arrested Meiosis II. The Periods are divided into six stages: Mitotic Division of Oogonia, Chromatin Nucleolus, Primary Growth, Secondary Growth, Oocyte Maturation and Ovulation. The Chromatin Nucleolus Stage is divided into four steps: Leptotene, Zygotene, Pachytene, and Early Diplotene. Oocytes in the last step possess one nucleolus, dispersed chromatin with forming lampbrush chromosomes and lack basophilic ooplasm. The Primary Growth Stage, characterized by basophilic ooplasm and absence of yolk in oocytes, is divided into five steps: One‐Nucleolus, Multiple Nucleoli, Perinucleolar, Oil Droplets, and Cortical Alveolar. During primary growth, the Balbiani body develops from nuage, enlarges and disperses throughout the ooplasm as both endoplasmic reticulum and Golgi develop within it. Secondary growth or vitellogenesis has three steps: Early Secondary Growth, Late Secondary Growth and Full‐Grown. The Oocyte Maturation Stage, including ooplasmic and germinal vesicle maturation, has four steps: Eccentric Germinal Vesicle, Germinal Vesicle Migration, Germinal Vesicle Breakdown and Resumption of Meiosis when complete yolk hydration occurs. The period is Arrested Meiosis II. When folliculogenesis is completed, the ovarian follicle, an oocyte and encompassing follicle cells, is surrounded by a basement membrane and developing theca, all forming a follicle complex. After ovulation, a newly defined postovulatory follicle complex remains attached to the germinal epithelium. It is composed of a basement membrane that separates the postovulatory follicle from the postovulatory theca. Arrested Meiosis I encompasses primary and secondary growth (vitellogenesis) and includes most of oocyte maturation until the resumption of meiosis (Active Meiosis II). The last stage, Ovulation, is the emergence of the oocyte from the follicle when it becomes an egg or ovum. J. Morphol. 2012. © 2012 Wiley Periodicals, Inc.     

Histochemical studies on the yolk-nucleus in fish oogenesis

Summary A histochemical study of the oogenesis of two species of fresh water fishes, Channa maruleus and Heteropneustes fossilis, was undertaken to reveal the origin, structure, histochemical nature, and function of the so-called yolk-nucleus. The basophilic substance of the yolk-nucleus, which is situated in the juxta-nuclear cytoplasm, gradually accumulates adjacent to the nuclear membrane. It is a homogeneous, spherical mass. In Channa, some basophilic, dense bodies develop in the yolk-nucleus. Histochemical tests show that the yolk-nucleus and dense bodies are rich in RNA and proteins. Mitochondria of lipoprotein composition and lipid inclusions, composed of unsaturated phospholipids, appear in association with the yolk-nucleus. Throughout previtellogenesis, the yolk-nucleus continues to proliferate its basophilic, RNA-containing substance and other inclusions. Finally it disintegrates while lying in the peripheral cytoplasm of the larger oocytes which show the synthesis of yolk bodies. During yolk formation, lipid inclusions and mitochondria start disappearing from view but the RNA-containing substance, originated from the yolk-nucleus of previtellogenesis, continues to persist among the growing yolk bodies. The latter arise de novo from the ground cytoplasm, under the influence of the RNA-containing substance, mitochondria and lipid inclusions of previtellogenesis.This work was carried out in the Department of Zoology, University of Gorakhpur, Gorakhpur, India.Population Council Post-Doctoral Fellow.     

Further morphological and histochemical studies on the yolk nucleus and associated cell components in the developing oocyte of the Indian wall lizard

In March through April when the oocyte growth in the ovaries of the wall lizard (Hemidactylus) is very rapid, the yolk nucleus continues to persist through various stages of previtellogenesis. This persisting yolk nucleus and associated cell components have been studied with histochemical techniques. The spherical and dense yolk nucleus stains for protein, lipoprotein and RNA. It does not form any close morphological association with the other cell components such as the mitochondria, lipid bodies (L₂), spaces or canals, diffuse sudanophilic substance and dense bodies, which are arranged into three zones round the yolk nucleus proper. The mitochondria stain for lipoprotein; the L₂ bodies consist of phospholipid; the spaces do not contain any material demonstrable with histochemical techniques; and the ooplasm containing the diffuse sudanophilic substance and dense bodies shows lipoprotein, protein and RNA. Eventually, the yolk nucleus disintegrates, and its substance as well as the other cell components are distributed in the cortical ooplasm of oocytes which are ready to form the yolk bodies. Concepts of the origin, morphology, cytochemistry and function of the yolk nucleus in the oocytes of invertebrates and vertebrates, which have come about recently through the application of cytochemical and submicroscopical techniques, are discussed.     

Oogenesis and ovarian histology in two populations of the viviparous lizard Sceloporus grammicus (Squamata: Phrynosomatidae) from the central Mexican Plateau

The annual histological changes in ovarian morphology (oogenesis, follicular atresia, and corpus luteum) are described for the Mexican lizard Sceloporus grammicus, in two populations that inhabit contrasting environments (vegetation categories, climate, precipitation, and temperature) from Hidalgo State, Mexico. Two germinal beds were situated on the dorsal surface of each ovary of this species. In both the populations, oogenesis involves two major processes: previtellogenesis and vitellogenesis. The histological changes during previtellogenesis are similar to those for other reptilian sauropsids, whereas vitellogenesis differs and the features of this last process are described for the first time. In early previtellogenesis, primary oocytes have fibrillar chromosomes and the ooplasm stains slightly. The primordial follicles are surrounded by a granulosa composed of cuboidal follicular cells. During late previtellogenesis, the oocyte had an eccentric nucleus with lamp‐brush chromosomes and multiple nucleoli. The granulosa becomes multilayered and polymorphic, containing three cell types: small, intermediate, and pyriform. The zona pellucida was homogeneous and clearly observed. In early vitellogenesis, the oocyte showed several small acidophilic granules distributed in the center and the periphery of the oocyte. As vitellogenesis progresses, the yolk platelets move toward the central area of the oocyte and they fuse to form acidophilic and homogeneous yolk. Lipid droplets were distributed irregularly in the ooplasm of the oocyte. In Zacualtipán, the results revealed a strong seasonal reproductive activity. Females had vitellogenic follicles from July to September, and pregnant females were founded from September to March. In Tizayuca, the results showed an unusual pattern of reproductive activity. Females with vitellogenic follicles and pregnant females were found throughout the year, indicating continuous reproduction. We suggest that the observed differences in reproductive activity from these populations indicate adaptative fine tuning in response to local environmental conditions. These results contribute to the knowledge of variation in vitellogenesis and reproductive strategies of this species and among spiny lizards overall. J. Morphol. 275:949–960, 2014. © 2014 Wiley Periodicals, Inc.     

Oogenesis in the viviparous matrotrophic lizard Mabuya brachypoda

Oogenesis in the lizard Mabuya brachypoda is seasonal, with oogenesis initiated during May-June and ovulation occurring during July-August. This species ovulates an egg that is microlecithal, having very small yolk stores. The preovulatory oocyte attains a maximum diameter of 0.9-1.3 mm. Two elongated germinal beds, formed by germinal epithelia containing oogonia, early oocytes, and somatic cells, are found on the dorsal surface of each ovary. Although microlecithal eggs are ovulated in this species, oogenesis is characterized by both previtellogenic and vitellogenic stages. During early previtellogenesis, the nucleus of the oocyte contains lampbrush chromosomes, whereas the ooplasm stains lightly with a perinuclear yolk nucleus. During late previtellogenesis the ooplasm displays basophilic staining with fine granular material composed of irregularly distributed bundles of thin fibers. A well-defined zona pellucida is also observed. The granulosa, initially composed of a single layer of squamous cells during early previtellogenesis, becomes multilayered and polymorphic. As with other squamate reptiles, the granulosa at this stage is formed by three cell types: small, intermediate, and large or pyriform cells. As vitellogenesis progresses the oocyte displays abundant vacuoles and small, but scarce, yolk platelets at the periphery of the oocyte. The zona pellucida attains its maximum thickness during late oogenesis, a period when the granulosa is again reduced to a single layer of squamous cells. The vitellogenic process observed in M. brachypoda corresponds with the earliest vitellogenic stages seen in other viviparous lizard species with larger oocytes. The various species of the genus Mabuya provided us with important models to understand a major transition in the evolution of viviparity, the development of a microlecithal egg.     

中国大鲵卵母细胞发育的显微和超微结构

用光镜和电镜观察了大鲵卵母细胞在发育过程中的显微和超微结构变化，着重对类核周体结构和线粒体与卵黄前颗粒的关系进行了详尽观察。贴近卵核的类核周体由核仁样体和线粒体群构成，远离卵核的类核周体仅由线粒体群构成。线粒体群是线粒增殖区，其中有多种形态的原线粒体，有些处于增殖状态，它们未形成明显的线粒体嵴。散在于卵质中的线粒体是成的线料体，有明显的嵴，其中许多线粒体内沉积着致密物质，一些致密物质从线粒体中向外     

Cytochemical and fine structural analysis of oogenesis in the gastropod, Ilyanassa obsoleta

An analysis of differentiating oocytes of the gastropod, Ilyanassa obsoleta, has been made by techniques of light and electron microscopy. Early previtellogenic oocytes are limited by a smooth surfaced oolemma and are associated with each other by maculae adhaerentes. Previtellogenic oocytes are also distinguished by a large nucleus containing randomly dispersed aggregates of chromatin. Within the ooplasm are Golgi complexes, mitochondria and a few cisternae of the rough endoplasmic reticulum. When vitellogenesis begins, the oolemma becomes morphologically specialized by the formation of microvilli. One also notices an increase in the number of organelles and inclusions such as lipid droplets. During vitellogenesis there is a dilation of the saccules of the Golgi complexes and cisternae of the endoplasmic reticulum. Associated with the Golgi complexes are small protein-carbohydrate yolk precursors encompassed by a membrane. These increase in size by fusing with each other. The “mature” yolk body is a membrane-bounded structure with a central striated core and a granular periphery. At maturity a major portion of the ooplasmic constituents such as as mitochondria and lipid droplets occupy the animal region while the bulk of the population of yolk bodies are situated in the vegetal hemisphere. The follicle cells incompletely encompass the developing oocyte. In addition to the regularly occurring organelles, follicle cells are characterized by the presence of large quantities of rough endoplasmic reticulum and Golgi complexes whose saccules are filled with a dense substance. Associated with the Golgi saccules are secretory droplets of varied size. Amongst the differentiating oocytes and follicle cells are Leydig cells. These cells are characterized by a large vacuole containing glycogen. A possible function for the follicle and Leydig cells is discussed.     

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.     

Structure of the germinal vesicle during oogenesis in leech Glossiphonia heteroclita (Annelida, Hirudinea, Rhynchobdellida)

Oogenesis in the glossiphoniid leech Glossiphonia heteroclita (Hirudinea, Rhynchobdellida) is nutrimental, i.e., the growing oocyte is supported by specialized germline cells, the nurse cells. The main function of the nurse cells is to provide oocytes with cell organelles and RNAs (mainly rRNA). However, in studied leech species, irrespective of the nutrimental mode of oogenesis, the germinal vesicle (GV = oocyte nucleus) seems to be very active in rRNA production. As shown in the present study, during early previtellogenesis in the GV the meiotic chromosomes and prominent primary nucleoli occur. In late previtellogenesis the chromosomes condense and occupy a limited space of nucleoplasm in close vicinity to primary nucleolus, forming a karyosome. At the onset of vitellogenesis several prominent extrachromosomal DNA bodies appear in close association with the karyosome. At the same time, the primary nucleolus is no longer visible in the GV. As vitellogenesis proceeds the extrachromosomal DNA bodies undergo fragmentation and numerous spherical, RNA- and AgNOR-positive inclusions occur in the nucleoplasm. They are regarded as multiple nucleoli. Finally, in late oogenesis numerous accessory nuclei are formed in close proximity to the nuclear envelope. They usually contain one dense body, morphologically similar to multiple nucleoli. The amplification of rDNA genes, the occurrence of extrachromosomal DNA bodies, as well as the presence of multiple nucleoli and accessory nuclei are described for the first time in the phylum Annelida.     

An autoradiographic and cytophotometric study of oogenesis in a pulmonate snail,Planorbarius corneus

Summary The spatial and temporal patterns of macromolecular syntheses in oocytes and somatic auxiliary cells of the snail Planorbarius corneus have been investigated by autoradiography and cytophotometry. Oogenesis has been divided into three stages, comprising early meiosis up to diplotene (stage I), previtellogenetic growth phase (stage II), and vitellogenesis (stage III). No DNA synthesis was found in any oocyte stage. In stage-I oocytes, only nucleoli were found labelled with ³H-uridine. Oocyte nuclei of stage II and III actively synthesize RNA in nucleoli and chromosomes. The most intense incorporation of uridine in chromatin probably occurs during the previtellogenesis — vitellogenesis transition period during which cytological findings suggest well developed lampbrush chromosomes. RNA synthesis in amphinucleoli of stage-III oocytes is restricted to basophilic nucleolar parts, whereas acidophilic parts (protein bodies) neither synthesize nor store RNA. During vitellogenesis oocytes incorporate amino acids into yolk platelet proteins. Radioactive proteins are found in yolk platelet precursors 5 h after injection of the tracer and in yolk platelets 3 h thereafter. The labelling pattern suggests that oocytes synthesize certain hitherto unidentified yolk components. No evidence for the participation of follicle cells in synthesis and transport of vitellogenic proteins has been obtained from autoradiography. Cytological findings suggest an important role for these cells in oogenesis. They are highly active in RNA and protein synthesis. Cellular differentiation is accompanied by polyploidization of the nuclei which attain a highest DNA content of 256 c. Polyploidization probably occurs in incremental steps as indicated by complete endomitotic chromosomal cycles. Autoradiographs show that, during vitellogenesis, oocytes do not incorporate significant amounts of glucose, and only certain follicle cells were labelled with glucose, probably indicating the synthesis of glycogen.     

Oogenesis in Acerentomon gallicum Jonescu (Protura)

Summary Late stages of oogenesis in Acerentomon gallicum Jonescu have been studied by means of light and electron microscopy. Each of the two ovaries of this species consists of a single panoistic ovariole. Late previtellogenic and early vitellogenic oocytes are enclosed in an electron opaque layer, the so-called primary sheath. The precursors for this sheath are most likely synthesized by follicle cells. The yolk develops through autosynthesis, with free ribosomes, dictyosomes and lamellar bodies being involved in the process. Mature yolk spheres contain proteins and polysaccharides. Besides the organelles that take part in vitellogenesis, mitochondria and cisternal stacks of the rough endoplasmic reticulum occur in the ooplasm.This work was supported by Government Problem Grant ii-1.3.13     

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。     

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。       

Ultrastructure of the ovarian follicles in the placentotrophic Andean lizard of the genus Mabuya (Squamata: Scincidae)

We studied the ultrastructural organization of the ovarian follicles in a placentotrophic Andean lizard of the genus Mabuya. The oocyte of the primary follicle is surrounded by a single layer of follicle cells. During the previtellogenic stages, these cells become stratified and differentiated in three cell types: small, intermediate, and large globoid, non pyriform cells. Fluid‐filled spaces arise among follicular cells in late previtellogenic follicles and provide evidence of cell lysis. In vitellogenic follicles, the follicular cells constitute a monolayered granulosa with large lacunar spaces; the content of their cytoplasm is released to the perivitelline space where the zona pellucida is formed. The oolemma of younger oocytes presents incipient short projections; as the oocyte grows, these projections become organized in a microvillar surface. During vitellogenesis, cannaliculi develop from the base of the microvilli and internalize materials by endocytosis. In the juxtanuclear ooplasm of early previtellogenic follicles, the Balbiani's vitelline body is found as an aggregate of organelles and lipid droplets; this complex of organelles disperses in the ooplasm during oocyte growth. In late previtellogenesis, membranous organelles are especially abundant in the peripheral ooplasm, whereas abundant vesicles and granular material occur in the medullar ooplasm. The ooplasm of vitellogenic follicles shows a peripheral band constituted by abundant membranous organelles and numerous vesicular bodies, some of them with a small lipoprotein core. No organized yolk platelets, like in lecithotrophic reptiles, were observed. Toward the medullary ooplasm, electron‐lucent vesicles become larger in size containing remains of cytoplasmic material in dissolution. The results of this study demonstrate structural similarities between the follicles of this species and other Squamata; however, the ooplasm of the mature oocyte of Mabuya is morphologically similar to the ooplasm of mature oocytes of marsupials, suggesting an interesting evolutionary convergence related to the evolution of placentotrophy and of microlecithal eggs. J. Morphol., 2010. © 2010 Wiley‐Liss, Inc.     

The ultrastructure of oogenesis and yolk formation in Labidocera aestiva (Copepoda: Calanoida)

Yolk formation in the oocytes of the free-living, marine copepod, Labidocera aestiva (order Calanoida) involves both autosynthetic and heterosynthetic processes. Three morphologically distinct forms of endogenous yolk are produced in the early vitellogenic stages. Type 1 yolk spheres are formed by the accumulation and fusion of dense granules within vesicular and lamellar cisternae of endoplasmic reticulum. A granular form of type 1 yolk, in which the dense granules within the cisternae of endoplasmic reticulum do not fuse, appears to be synthesized by the combined activity of endoplasmic reticulum and Golgi complexes. Type 2 yolk bodies subsequently appear in the ooplasm but their formation could not be attributed to any particular oocytic organelle. In the advanced stages of vitellogenesis, a single narrow layer of follicle cells becomes more developed and forms extensive interdigitations with the oocytes. Extra-oocytic yolk precursors appear to pass from the hemolymph into the follicle cells and subsequently into the oocytes via micropinocytosis. Pinocytotic vesicles fuse in the cortical ooplasm to form heterosynthetically derived type 3 yolk bodies.     

Oogenesis of microlecithal oocytes in the viviparous teleost Heterandria formosa

Viviparous teleosts exhibit two patterns of embryonic nutrition: lecithotrophy (when nutrients are derived from yolk that is deposited in the oocyte during oogenesis) and matrotrophy (when nutrients are derived from the maternal blood stream during gestation). Nutrients contained in oocytes of matrotrophic species are not sufficient to support embryonic development until term. The smallest oocytes formed among the viviparous poeciliid fish occur in the least killifish, Heterandria formosa, these having diameters of only 400 μm. Accordingly, H. formosa presents the highest level of matrotrophy among poeciliids. This study provides histological details occurring during development of its microlecithal oocytes. Five stages occur during oogenesis: oogonial proliferation, chromatin nucleolus, primary growth (previtellogenesis), secondary growth (vitellogenesis), and oocyte maturation. H. formosa, as in all viviparous poeciliids, has intrafollicular fertilization and gestation. Therefore, there is no ovulation stage. The full‐grown oocyte of H. formosa contains a large oil globule, which occupies most of the cell volume. The oocyte periphery contains the germinal vesicle, and ooplasm that includes cortical alveoli, small oil droplets and only a few yolk globules. The follicular cell layer is initially composed of a single layer of squamous cells during early previtellogenesis, but these become columnar during early vitellogenesis. They are pseudostratified during late vitellogenesis and reduce their height becoming almost squamous in full‐grown oocytes. The microlecithal oocytes of H. formosa represent an extreme in fish oogenesis typified by scarce yolk deposition, a characteristic directly related to matrotrophy. J. Morphol., 2011. © 2010 Wiley‐Liss, Inc.     

Oocyte-follicle cell differentiation in two species of amphineurans (Mollusca), Mopalia mucosa and Chaetopleura apiculata

Differentiating oocytes and associated follicle cells of two species of amphineurans (Mollusca) Mopalia muscosa and Chaetopleura apiculata have been studied by techniques of light and electron microscopy. In addition to the regularly occurring organelles, the ooplasm of young oocytes contains large, randomly situated, basophilic regions. These regions are not demonstrable in mature eggs. As oocytes differentiate, lipid, pigment and protein-carbohydrate yolk bodies accumulate within the ooplasm. Concomitant with the appearance of pigment and the protein carbohydrate containing yolk bodies, the saccules of the Golgi complex become filled with a dense material. Associated with the Golgi complex are cisternae of the rough endoplasmic reticulum which are filled with an electron opaque substance which is thought to be composed of protein synthesized by this organelle. That portion of the cisternae of the endoplasmic reticulum facing the Golgi complex shows evaginations. These evaginations are thought to finalize into protein containing vesicles that subsequently fuse with the Golgi complex. Thus, the Golgi complex in these oocytes might serve as a center for packaging and concentrating the protein used in the construction of the protein containing pigment or protein-carbohydrate yolk bodies. The suggestion is made that the Golgi complex may also synthesize the carbohydrate portion of the formentioned yolk bodies. In an adnuclear position in young oocytes are some acid mucopolysaccharide containing vacuolar bodies. In mature eggs, these structures are found within the peripheral ooplasm and we have referred to them as cortical granules. There is no alteration of these cortical granules during sperm activation.     

Gap junctions between the follicle cells and the oocyte during oogenesis in an insect,Tribolium destructor/Coleoptera

Summary Oocyte-follicle cell gap junctions inTribolium occur in all oogenetic stages studied. During early previtellogenesis the junctions are found exclusively between lateral membranes of oocyte microvilli and the membrane of prefollicle cells. In late previtellogenesis and vitellogenesis the junctions are located between the tips of oocyte microvilli and the flat membranes of the follicle cells. During previtellogenesis gap junctions are infrequent, whereas in the phase of yolk accumulation their number increases considerably, exceeding 17 junctions/m² of the follicle cell membrane. It could be shown by microinjection of a fluorescent dye that gap junctions are in a functional state during vitellogenesis. Possible roles of heterologous gap junctions in oogenesis are discussed.     

Previtellogenic oocytes of South African largemouth bass Micropterus salmoides Lacépède 1802 (Actinopterygii,Perciformes) - the Balbiani body,cortical alveoli and developing eggshell

The ovaries of the largemouth bass Micropterus salmoides, an alien and invasive species in South Africa, contain a germinal epithelium which consists of germline and somatic cells, as well as previtellogenic and late vitellogenic ovarian follicles. The ovarian follicle consists of an oocyte surrounded by follicular cells and a basal lamina; thecal cells adjacent to this lamina are covered by an extracellular matrix. In this article, we describe the Balbiani body and the polarization and ultrastructure of the cytoplasm (ooplasm) in previtellogenic oocytes. The nucleoplasm in all examined oocytes contains lampbrush chromosomes, nuclear bodies and several nucleoli near the nuclear envelope. The ultrastructure of the nucleoli is described. Numerous nuage aggregations are present in the perinuclear cytoplasm in germline cells as well as in the ooplasm. Possible roles of these aggregations are discussed. The ooplasm contains the Balbiani body, which defines the future vegetal region in early previtellogenic oocytes. It is comprised of nuage aggregations, rough endoplasmic reticulum, Golgi apparatus, mitochondria, complexes of mitochondria with nuage-like material, and lysosome-like organelles. In mid-previtellogenic oocytes, the Balbiani body surrounds the nucleus and later disperses in the ooplasm. The lysosome-like organelles fuse and transform into vesicles containing material which is highly electron dense. As a result of the fusion of the vesicles of Golgi and rough endoplasmic reticulum, the cortical alveoli arise and distribute uniformly throughout the ooplasm of late previtellogenic oocytes. During this stage, the deposition of the eggshell (zona radiata) begins. The eggshell is penetrated by canals containing microvilli and consists of the following: the internal and the external egg envelope. In the external envelope three sublayers can be distinguished.     

Carbohydrate and protein histochemistry during oogenesis inHalobatrachus didactylus (Schneider, 1801) from the Bay of Cadiz (Spain)

Summary Histological and histochemical characteristics were studied inHalobatrachus didactylus (Schneider, 1801) during oogenesis. Three phases could be differentiated: previtellogenesis (oogonia and basophilic oocytes), vitellogenesis (yolk synthesis) and maturation-spawning. Glycogen, glycoproteins and proteins rich in certain amino acids were present in the previtellogenic as well as in the vitellogenic cytoplasm oocytes. No acid mucosubstances were detected. Three types of yolk (vesicles, vacuoles and granules) contained different types of organic reserves; granules were essentially proteic whereas globules were lipidic. Carbohydrates and proteins were present in vesicles.