Ultrastructural study of oogenesis in Monocelis lineata (Turbellaria,Proseriata)

Summary

Oogenesis in the marine turbellarian proseriat Monocelis lineata was investigated at the ultrastructural level. Oocyte differentiation is not synchronous so that successive stages of germ cell maturation were simultaneously detected in each of the two ovaries. Each developing oocyte is enveloped by follicle cell projections which are presumably involved in a morphologically undetectable support of vitellogenesis. The main features evidenced during oocyte differentiation are: (1) The synthesis of cortical granules by the rough endoplasmic reticulum and Golgi complex, occurring in the earlier stages of oogenesis; (2) The synthesis of yolk globules by the rough endoplasmic reticulum (RER) and Golgi complex, occurring in the later stages of oogenesis, namely late meiotic prophase I. Neither morphologically visible endocytotic activity, nor the presence of intercellular bridges, nor even the development of microvilli were observed at the oolemma or cortical ooplasm, so that the sole mechanism of vitellogenesis appears to be autosynthetic. The significance of these findings is discussed in relation to the taxonomic position of M. lineata and more generally in relation to the phylogenetic history of the class Turbellaria.     

Regulation of the vitellogenin receptor during Drosophila melanogaster oogenesis

In many insects, development of the oocyte arrests temporarily just before vitellogenesis, the period when vitellogenins (yolk proteins) accumulate in the oocyte. Following hormonal and environmental cues, development of the oocyte resumes, and endocytosis of vitellogenins begins. An essential component of yolk uptake is the vitellogenin receptor. In this report, we describe the ovarian expression pattern and subcellular localization of the mRNA and protein encoded by the Drosophila melanogaster vitellogenin receptor gene yolkless (yl). yl RNA and protein are both expressed very early during the development of the oocyte, long before vitellogenesis begins. RNA in situ hybridization and lacZ reporter analyses show that yl RNA is synthesized by the germ line nurse cells and then transported to the oocyte. Yl protein is evenly distributed throughout the oocyte during the previtellogenic stages of oogenesis, demonstrating that the failure to take up yolk in these early stage oocyte is not due to the absence of the receptor. The transition to the vitellogenic stages is marked by the accumulation of yolk via clathrin-coated vesicles. After this transition, yolk protein receptor levels increase markedly at the cortex of the egg. Consistent with its role in yolk uptake, immunogold labeling of the receptor reveals Yl in endocytic structures at the cortex of wild-type vitellogenic oocytes. In addition, shortly after the inception of yolk uptake, we find multivesicular bodies where the yolk and receptor are distinctly partitioned. By the end of vitellogenesis, the receptor localizes predominantly to the cortex of the oocyte. However, during oogenesis in yl mutants that express full-length protein yet fail to incorporate yolk proteins, the receptor remains evenly distributed throughout the oocyte.     

Oogenesis: From Oogonia to Ovulation in the Flagfish,Jordanella floridae Goode and Bean, 1879 (Teleostei: Cyprinodontidae)

We provide histological details of the development of oocytes in the cyprinodontid flagfish, Jordanella floridae. There are six stages of oogenesis: Oogonial proliferation, chromatin nucleolus, primary growth (previtellogenesis [PG]), secondary growth (vitellogenesis), oocyte maturation and ovulation. The ovarian lamellae are lined by a germinal epithelium composed of epithelial cells and scattered oogonia. During primary growth, the development of cortical alveoli and oil droplets, are initiated simultaneously. During secondary growth, yolk globules coalesce into a fluid mass. The full‐grown oocyte contains a large globule of fluid yolk. The germinal vesicle is at the animal pole, and the cortical alveoli and oil droplets are located at the periphery. The disposition of oil droplets at the vegetal pole of the germinal vesicle during late secondary growth stage is a unique characteristic. The follicular cell layer is composed initially of a single layer of squamous cells during early PG which become columnar during early vitellogenesis. During primary and secondary growth stages, filaments develop among the follicular cells and also around the micropyle. The filaments are seen extending from the zona pellucida after ovulation. During ovulation, a space is evident between the oocyte and the zona pellucida. Asynchronous spawning activity is confirmed by the observation that, after ovulation, the ovarian lamellae contain follicles in both primary and secondary growth stages; in contrast, when the seasonal activity of oogenesis and spawning ends, after ovulation, the ovarian lamellae contain only follicles in the primary growth stage. J. Morphol. 277:1339–1354, 2016. © 2016 Wiley Periodicals, Inc.     

Differentiation of cytoplasmic organelles and storage of yolk during vitellogenesis in Hemidiaptomus ingens and Mixodiaptomus kupelwieseri (Copepoda,Calanoida)

These investigations concern two freshwater calanoid copepods Hemidiaptomus ingens and Mixodiaptomus kupelwieseri. The first aspect of the research relates to the processes involved in the formation and the differentiation of the ooplasmic organelles at the time of primary vitellogenesis. During this phase, a number of complex associations develop in the ooplasm. They consist chiefly of nuage-like structures, corresponding to extruded nuclear material, and vesicular formations, some arising from the nuclear envelope and the others neoformed in the ooplasm. These associations represent centers of maturation for ribosomes and synthesis for reticulum membranes. Annulate lamellae may be observed near these associations. Biogenesis of the reticulum always precedes the differentiation of the Golgi apparatus. Indeed, the dictyo-somes develop in characteristic complexes including endoplasmic reticulum cisternae and numerous vesicles resulting from intensive blebbing from cisternae. The second aspect of this research concerns yolk synthesis and accumulation of hyaloplasmic inclusions. A preliminary synthesis of yolk occurs early in these complexes and becomes more important after achievement of Golgi apparatus biogenesis. However, the most important yolk storage results from exogenous molecules and consists of complex globules, which develop into the ooplasm during secondary vitellogenesis. Formation of these globules is associated with the accumulation of two categories of inclusions in the hyaloplasm, i.e., lipid droplets and clusters of glycogen particles. At the end of vitellogenesis, a new type of endogenous material develops into small cisternae localized in the cortical ooplasm. © 1993 Wiley-Liss, Inc.     

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.     

Ultrastructural observation of oogenesis in the crustacea amphipoda Orchestia gammarellus (Pallas)

The oogenesis of the Crustacea Amphipoda Orchestia gammarellus can be divided in five stages taking into consideration both the oocyte ultrastructure and the physiology of the ovary. The primary oogonium (12 μm in diameter) is lodged within the germinative zone: after division, the daughter cell (or secondary oogonium) leaves this area and enters meiotic prophase. Stage I is represented by the oocyte with visible chromosomes (12–18 μm in diameter) the cytoplasmic ultrastructure of which is comparable to that of the oogonium. Stage II or previtellogenesis is characterized by a considerable growth of the oocyte (18–80 μm in diameter) which becomes enriched in ribosomes and vesicles of the rough endoplasmic reticulum; the oocyte does not yet contain any vitelline reserve (proteinaceous and lipid). Stage III or primary vitello-genesis (80–160 μm in diameter) is typified by the synthetic activity of the rough endoplasmic reticulum, corresponding to an endogenous accumulation of proteinaceous yolk. Stage IV or secondary vitellogenesis (160–800 μm in diameter) only appears during the period of reproduction; by means of endocytosis the oocyte accumulates yolk spheres in addition to lipid droplets, the origin of which is uncertain; towards the end of vitellogenesis, cortical granules become a feature that is noted for the first time in Crustacea. The last stage or maturation (800 μm in diameter) starts right before or immediately after the exuviation of the female and ends with fertilization.     

Morphology and ultrastructure of the adult ovarian cycle in Mithracidae (Crustacea,Decapoda, Brachyura,Majoidea)

The ultrastructure of the ovary during development and yolk production is poorly known in Brachyura and Majoidea in particular. Here, we describe the histology, histochemistry and ultrastructure of the adult ovarian cycle in four Mithracidae species from three different genera: Mithrax hispidus, Mithrax tortugae, Mithraculus forceps and Omalacantha bicornuta. All species showed a similar pattern of ovarian development and vitellogenesis. Macroscopically, we detected three stages of ovarian development: rudimentary (RUD), developing (DE) and mature (MAT); however, in histological and ultrastructural analyses, we identified four stages of development. The oocytes of the RUD stage, during endogenous vitellogenesis, have basophilic cytoplasm filled with dilated rough endoplasmic reticulum. The reticulum lumen showed many granular to electron-dense materials among the different stages of development. The Golgi complexes were only observed in the RUD stage and are responsible for releasing vesicles that merge to the endogenous or immature yolk vesicles. At the early DE stage, the oolemma showed many coated and endocytic vesicles at the cortex. The endocytic vesicles merge with the endogenous yolk to form the exogenous or mature yolk vesicles, always surrounded by a membrane, characterizing exogenous vitellogenesis. The exogenous yolk vesicles comprise glycoproteins, showing only neutral polysaccharides. At the late DE stage, endocytosis still occurs, but the amount of endogenous yolk decreases while the exogenous yolk increases. The late DE stage is characterized by the beginning of chorion production among the microvilli. The MAT stage is similar to the late DE, but the endogenous yolk is restricted to a few cytoplasmic areas, the ooplasma is filled with exogenous yolk, and the oolemma has very few coated vesicles. In the MAT stage, the chorion is fully formed and shows two electron-dense layers. The ovarian development of the species studied has many similarities with the very little known Majoidea in terms of the composition, arrangement and increment of the yolk vesicles during oocyte maturation. The main differences are in the vitellogenesis process, where immature yolk formation occurs without the direct participation of the mitochondria but with the participation of the rough endoplasmic reticulum in the endogenous phase.     

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.     

Ultrastructural observations on oogenesis in Drosophila

The ultrastructure of the follicle cells and oocyte periplasm is described during the stages of oogenesis immediately prior to, during, and immediately subsequent to, vitellogenesis. A number of features have not been described previously in Drosophila. Some yolk appears prior to pinocytosis of blood proteins. However, most of the protein yolk forms while the periplasm is filled with micropinocytotic invaginations and tubules derived from the oolemma. These tubules retain the internal layer of material characteristic of coated vesicles and are found to fuse with yolk spheres. No accumulation of electron-dense material in the endoplasmic reticulum or Golgi of the oocyte is found. Both trypan blue and ferritin are accumulated by the oocyte. The follicle cells have an elaborate endoplasmic reticulum during the period of maximum yolk accumulation. Adjacent cells are joined at their base by a zonula adhaerens, forming a band around the cells, and by plaques of gap junctions. Gap junctions are also present between nurse cells and follicle cells. During chorion formation, septate junctions also appear between follicle cells, adjacent to the zonula adhaerens.     

INTRACELLULAR SYNTHESIS, TRANSPORT, AND PACKAGING OF PROTEINACEOUS YOLK IN OOCYTES OF ORCONECTES IMMUNIS

The incorporation of leucine-³H into either ovarian or oocyte proteins occurs throughout vitellogenesis, but is at a maximum during early phases of this process. The labeling of ovarian and oocyte proteins is inhibited with cycloheximide. Oocytes are permeable to actinomycin D, and this drug does not affect the incorporation of amino acids into oocyte proteins but does block oocyte RNA synthesis. By means of both light microscope and high resolution radioautography, it has been demonstrated that the initial incorporation of leucine-³H under both in vitro and in vivo conditions occurs in elements of the rough-surfaced endoplasmic reticulum in the oocyte. Under pulse-chase conditions, the label subsequently becomes associated with intracisternal (precursor yolk) granules now aggregated within the cisternae of the connected smooth-surfaced endoplasmic reticulum. By 7 days, mature yolk globules are extensively labeled. The results of experiments designed to assess the possible contribution of maternal blood proteins to yolk deposition indicate that such a contribution is minimal. It is concluded that the crayfish oocyte is programmed for and capable of synthesizing the massive store of proteinaceous yolk present in the egg at the end of oogenesis.     

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.     

An ultrastructural study of oogenesis in a marine triclad

The ultrastructural features of oocyte differentiation were studied in the marine triclad Cercyra hastata. Oocytes at several stages of maturation, each surrounded by follicle cell projections, are present within each of the two ovaries. A pre-vitellogenic and a vitellogenic stage have been detected in the oogenesis of C. hastata. The pre-vitellogenic stage is mainly characterized by an increase in the nuclear and nucleolar volume and activity, and the appearance and development of cortical granule precursors which are elaborated by the Golgi complex. In early phases of the vitellogenic stage, intense delamination and blebbing of the nuclear envelope occurs which probably contributes to an increase in number of cytoplasmic membranes and to transfer of nuclear material to the cytoplasm. The rough endoplasmic reticulum is extensively developed and often assumes a ‘whorl’ array. Several areas of yolk precursor formation appear in the whorls. Numerous 2–5 μm protein yolk globules are subsequently formed which appear surrounded by a double membrane (cisternae of the smooth endoplasmic reticulum) and become randomly distributed throughout the cytoplasm of mature oocytes. The peripheral ooplasm is occupied by a monolayer of electron-dense cortical granules. Finally, the evolutionary significance of the autosynthetic mechanism of yolk production is discussed.     

莫桑比克非鲫卵黄形成的电镜观察

运用透射电镜观察了莫桑比克非鲫卵母细胞的生长.根据卵母细胞的大小和内部结构特征,将其分为四个时期:卵母细胞生长早期:卵黄泡形成期:卵黄积累期:卵黄积累完成期.本文着重研究了主要卵黄成分--卵黄球的形成过程.卵黄球属外源性卵黄,由卵母细胞通过微胞饮作用吸收肝脏合成的卵黄蛋白原后形成的.在卵黄大量积累前,卵母细胞内的线粒体和多泡体聚集成团,构成卵黄核,继而线粒体大量增殖,线粒体形状发生改变,形成同心多层膜结构,为大量的卵黄物质积累提供场所.最终形成的卵黄球由被膜、卵黄结晶体和两者之间的非结晶区三部分组成.       

北京油葫芦卵子发生中DNA及RNA动态变化研究

用孚尔根及甲基绿 -派洛宁组织化学染色法了解北京油葫芦Teleogryllusmitratus(Burmeister)卵子发生各时期阶段中卵内DNA及RNA动态变化规律。在卵子发生的最初阶段 ,核中DNA的合成和复制最活跃 ,以后便慢慢减弱 ;而RNA则在第 2阶段合成最旺盛。在卵子发生各个阶段 ,滤泡细胞中DNA ,RNA均为阳性反应 ,并在卵细胞的卵黄形成期活动旺盛 ,为卵母细胞卵黄蛋白形成提供物质基础。卵子发生第 4～ 6阶段 ,滤泡细胞开放时期 ,血淋巴内一些物质可能直接或间接通过滤泡细胞间隙进入卵母细胞内 ,参与卵母细胞的发育和构建。研究表明卵子发生初期卵母细胞的发育和物质构建主要以内源性合成积累为主 ,中后期则有外源性物质的参与。     

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.     

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.     

不同发育时期哲罗鱼卵黄的超微结构

应用透射电镜观察了不同发育时期哲罗鱼(Hucho taimen)卵黄的超微结构.根据哲罗鱼卵黄物质在卵母细胞中的加工合成、积累以及卵母细胞中参与卵黄颗粒形成的细胞器的变化,可将该鱼卵黄发生分为4个特征时期,即卵黄发生前期、卵黄泡期、卵黄积累期和卵黄积累完成期.卵黄发生前期是指卵母细胞发育过程中的卵黄物质开始积累前的时期,此时期核仁不断分裂,出现线粒体云和早期的滤泡细胞层、基层和鞘细胞层;卵黄泡期特点主要是细胞器不断变化产生卵黄泡和皮层泡;卵黄积累期的滤泡膜由内向外依次为放射带、颗粒细胞层、基层和鞘细胞层,此时外源性卵黄前体物质不断经过血液汇集于鞘细胞层,后经微胞饮作用穿过胶原纤维组成的基层,经过多泡体作用转运至颗粒细胞内,在细胞内经过加工和修饰形成小的卵黄蛋白颗粒,卵黄蛋白颗粒经微胞饮穿过放射带进入卵母细胞边缘形成的空泡中,不断积累形成卵黄球;进入卵黄积累完成期,卵黄球体积变大,向细胞中心聚集,填满大部分卵母细胞,卵黄积累完毕.     

A light and electron microscope study on oogenesis in the freshwater pulmonate snail Biomphalaria glabrata

In the freshwater snail Biomphalaria glabrata the formation and composition of yolk granules and the role of the follicle cells were studied by histochemical and electron microscopical techniques. The rough endoplasmic reticulum and the Golgi apparatus appeared to be involved in yolk formation, which is a continuous process throughout oogenesis. From the very beginning of yolk formation two main types of yolk granules were distinguished morphologically. However, with histochemical and enzyme cytochemical methods no differences were observed between these types. The granules acquire lysosomal enzymes after oviposition, indicating that their main function is probably digestion of perivitelline fluid, which contains nutrients for the developing embryo.Yolk formation and the activity of the follicle cells were studied in successive stages of oogenesis by quantitative electron microscopy. The data strongly suggest that the follicle cells are involved in the formation of the follicular cavity and hence in the ovulation process.     

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.     

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.