A comparative histochemical study of fish (Channa maruleus) and amphibian (Bufo stomaticus) oogenesis

Summary Comparative histochemical studies on the fish (Channa maruleus) and amphibian (Bufo stomaticus) oogenesis demonstrate a great similarity in the growth and differentiation of their egg follicle. The ooplasm, germinal vesicle and egg-membranes show distinct morphological and cytochemical changes during previtellogenesis and vitellogenesis.During previtellogenesis the various components of the follicle are engaged in the synthesis of protoplasm as shown by the proliferation of yolk nucleus substance, mitochondria and some lipid bodies in the ooplasm and of nucleoli in the germinal vesicle. The substance of the yolk nucleus consisting of proteins, lipoproteins and RNA first appears adjacent to the nuclear membrane. Numerous mitochondria of lipoprotein composition, and some lipid bodies consisting of unsaturated phospholipids lie in association with the yolk nucleus which forms substratum for the former. The lipid bodies, present inside the germinal vesicle, follicular epithelium, and adjacent to the plasma membrane in association with some pinocytotic vacuoles, have been considered to play a significant role in the active transport of some substances from the environment into the ooplasm and from the latter into the germinal vesicle. The follicular epithelium itself is very poorly developed, negating its appreciable role in the contribution of specific substances into the oocyte, which seem to be contributed by the germinal vesicle showing a considerable development of nuclear sap, basophilic granules and nucleoli consisting of RNA and proteins; many large nucleoli bodily pass into the cytoplasm during the previtellogenesis of Channa, where their substance is gradually dissolved. The intense, diffuse, basophilic substance of the cytoplasm is believed due to free ribosomes described in many previous ultrastructural studies.During vitellogenesis, the various deutoplasmic inclusions, namely carbohydrate yolk, proteid yolk and fatty yolk, are deposited in the ooplasm. The carbohydrate yolk bodies rich in carbohydrates originate in association with the plasma membrane and correspond to vesicles and cortical granules of previous studies. The proteid yolk consisting of proteins and some lipoproteins, and fatty yolk containing first phospholipids and some triglycerides and then triglycerides only are deposited under the influence of yolk nucleus substance, mitochondria and cytoplasm. The mitochondria and yolk nucleus substance foreshadow in some way the pattern of these two deutoplasmic inclusions and persist at the animal pole of mature egg while the other inclusions of previtellogenesis disappear from view. The pigment granules, which also show a gradient from the animal to vegetal pole in Bufo, are also formed in association with yolk nucleus substance and mitochondria. Some glycogen also appears in both the species. The nuclear membrane becomes irregular due to the formation of lobes. The lipid bodies of the germinal vesicle come to lie outside the nuclear membrane, suggesting active transport of some substances into the ooplasm; many nucleoli bodily pass into the ooplasm of Bufo, where they are gradually absorbed. The amount of basophilic granules is considerably increased in the germinal vesicle during vitellogenesis. Various egg-membranes such as outer epithelium, thin theca, single-layered follicular epithelium, zona pellucida or vitelline membrane surround the vitellogenic oocytes. The zona pellucida formed between the oocyte and follicle cells consists of a carbohydrate-protein complex. The follicle cells show lipid droplets, mitochondria and basophilic substance in their cytoplasm. The various changes that occur in the components of the follicle during vitellogenesis seem to be initiated by gonadrotrophins formed under the influence of specific environmental conditions.The author wishes to express sincere appreciation and gratitude to Dr. Gilbert S. Greenwald, who has made the completion of this investigation possible.Ph. D. Population Council Post-doctoral Fellow.     

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     

Some observations on the development and cyclic changes of the oöcytes in a brooding starfish, Leptasterias hexactis

There are two ovaries in each arm and each ovary bears a single oviduct which opens orally at the interradial angle. The ovarian wall consists of three layers: mesothelium, muscular-connective tissue layer and germinal epithelium. The haemal space between the germinal epithelium and muscular-connective tissue layer is filled with a PAS positive fluid. It is suggested that this space may provide storage and transportation of nutrient to the germ cells.
The oögonium, situated along the germinal epithelium, is distinguished from the surrounding follicle cells by its clear cytoplasm and large nucleus with a single nucleolus. It measures 10 to 15 μ in diameter.
The development of primary oöcytes is divided into premeiotic, growth and germinal vesicle migration stages. The distribution of mitochondria seems to indicate the existence of a definite polarity in the young oöcytes; but this soon disappears at the beginning of vitellogenesis. Morphological evidence seems to suggest that some of the yolk granules may be synthesized first in follicle cells and then transferred into the oöcyte. Histochemical tests indicate that the yolk platelet is a carbohydrate-protein-lipid complex.
The first meiotic division occurs six hours after sperm penetration and the second meiotic division follows two hours later.
Monthly measurement of the oöcyte throughout a year indicates a well-defined annual spawning cycle; however, the growth of an oöcyte from an oögonium to a mature oöcyte requires about two years.     

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.     

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.       

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。       

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。     

Ultrastructural study of oogenesis and yolk formation in an opisthobranch mollusc, Runcina

Runcina is a hermaphroditic opisthobranch mollusc of small size. It produces large eggs, rich in yolk substances, and it is thus ideal for studying the mechanisms of vitellogenesis. The rough endoplasmic reticulum and the Golgi apparatus appear to be involved in early build up of yolk precursors. Endocytotic vesicles carrying yolk proteins, taken up from the haemolymph, dominate yolk formation at a later stage. The findings presented in this study enhance the proposition of a dual pathway of auto- and heterosynthesis in yolk formation. It is not found that the yolk bodies in Runcina acquire lysosomal enzymes in order to digest the perivitelline fluid, as has been described for some pulmonates. The importance of the role played by the follicle cells in oocyte development is discussed.     

Yolk nucleus – The complex assemblage of cytoskeleton and ER is a site of lipid droplet formation in spider oocytes

Oocytes (future egg cells) of various animal groups often contain complex organelle assemblages (Balbiani bodies, yolk nuclei). The molecular composition and function of Balbiani bodies, such as those found in the oocytes of Xenopus laevis, have been recently recognized. In contrast, the functional significance of more complex and highly ordered yolk nuclei has not been elucidated to date. In this report we describe the structure, cytochemical content and evolution of the yolk nucleus in the oocytes of a common spider, Clubiona sp. We show that the yolk nucleus is a spherical, rather compact and persistent cytoplasmic accumulation of several different organelles. It consists predominantly of a highly elaborate cytoskeletal scaffold of condensed filamentous actin and a dense meshwork of intermediate-sized filaments. The yolk nucleus also comprises cisterns of endoplasmic reticulum, mitochondria, lipid droplets and other organelles. Nascent lipid droplets are regularly found in the cortical regions of the yolk nucleus in association with the endoplasmic reticulum. Single lipid droplets become surrounded by filamentous cages formed by intermediate filaments. Coexistence of the forming lipid droplets with the endoplasmic reticulum in the cortical zone of the yolk nucleus and their later investment by intermediate-sized filamentous cages suggest that the yolk nucleus is the birthplace of lipid droplets.     

Amblyomma triste (Koch, 1844) (Acari: Ixodidae): morphological description of the ovary and of vitellogenesis

The present study presents the morphology, histology, and the dynamics of vitellogenesis in females of the tick Amblyomma triste. The ovary in this species is of the panoistic type, therefore it lacks nurse cells. It is composed of a layer of epithelial cells that outwardly form the wall of the ovary, but also originate the pedicel, the structure that attaches the oocytes to its external margin, as well the oocytes themselves. In Amblyomma triste, the oocytes develop in four synchronic stages, which differs from the process in other tick species. The classification of the stages of the oocytes was carried out based on the presence of four morphologic characteristics: cytoplasm appearance; site of the germ vesicle; presence, quantity, and constitution of the yolk granules and presence of chorium.     

棉铃虫卵巢形态与卵子发生过程观察

害虫发生高峰期、 发生量的准确预测和田间防治适期的确定与种群雌虫卵巢结构及卵子发生过程密切相关。为了明确棉铃虫Helicoverpa armigera卵巢结构及卵子发生过程, 本研究利用光学体视显微镜和透射电子显微镜, 对棉铃虫成虫卵巢管和卵子的超微结构进行了研究, 并确定了发育级别划分标准。结果表明: 根据卵巢的形状、 卵的产生过程、 卵黄沉积情况等将棉铃虫卵巢发育程度分为6个级别, 即发育初期(0级)、 卵黄沉积前期(Ⅰ级)、 卵黄沉积期(Ⅱ级)、 成熟待产期(Ⅲ级)、 产卵盛期(Ⅳ级)和产卵末期(Ⅴ级)。根据卵子发生过程中滋养细胞、 卵母细胞的变化, 将卵子发生期分为3个阶段： 卵黄发生前期、 卵黄发生期和卵黄成熟期。本研究首次对棉铃虫的卵子发生进行电子显微观察, 并完善了棉铃虫卵巢发育的分级标准, 为进一步研究棉铃虫的生殖发育机理提供了理论参考, 对田间棉铃虫种群发生期和发生量的预测预报也有重要的实践参考价值。     

The histological and histochemical studies on the ovary in relation to vitellogenesis in the dragonfly, Orthetrum chrysis Selys (Libellulidae: Odonata).

The ovaries consist of large number of panoistic ovarioles in the last instar nymph and the adult dragonfly Orthetrum chrysis (Selys). In the nymph the vitellaria are compactly filled with the primary oocytes and the vitellogenesis takes place only in the adult stage. During vitellogenesis oocytes change widely in their shape, size and cytological organisation and their developmental stages can be divided into pre-vitellogenic, early-vitellogenic, vitellogenic, late-vitellogenic and maturation age. PAS-positive material appears first around the germinal vesicle in the early-vitellogenic stage and lateron it migrates towards the periphery. Glycogen appears in the late-vitellogenic stage. DNA is abundantly present in the nuclei of the oocytes during the pre-vitellogenic and completely absent in early-vitellogenic, vitellogenic, late-vitellogenic and maturation stages. It is observed in the nuclei of follicular epithelial cells of all the stages. RNA is abundantly present in cytoplasm of the pre-vitellogenic oocytes but lateron is gradually decreases. During the early-vitellogenic and vitellogenic stages high concentration of RNA in the follicular epithelial cells has been observed. The protein bodies appear first in the interfollicular spaces and towards the periphery of the oocytes just near the enveloping follicular epithelial cells, during the early-vitellogenic stage suggesting the formation of yolk proteins from the haemolymph. In Orthetrum chrysis the sudanophilic bodies appear first in the follicular cells and then lie in the peripheral region of the oocytes suggesting the incorporation of yolk lipid either from the follicular epithelium or from the haemolymph through the follicular epithelium. The phospholipids are synthesised in pre-vitellogenic to the late-vitellogenic stages. In the late-vitellogenic stages the phospholipid granules are present abundantly in the follicular epithelium while in the maturation stage they disappear suggesting their utilisation in the formation of membranes like vitelline and chorion. The neutral fats are present in the form of large number of droplets in the oocytes during the maturation stage.     

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.     

养殖鲥鱼性腺发育的研究

经激素处理和生态调控的养殖鲥鱼,能完成性腺发育的全过程,其可分为６个时期,卵细胞发育可相应分为６个时相。与其它鱼类不同,细胞中液泡最早出现在胞质的内缘而不是外缘。大、小核仁数随卵母细胞的发育而变化。成熟卵巢成熟系数为８５４％～１２６４％。成熟期卵径为６２８５～８３５３μｍ、精子头径为０７４～１５５μｍ。达性成熟的鲥鱼,冬季卵巢为Ⅱ期、精巢为Ⅱ～Ⅲ期。精、卵巢发育呈现出明显的不同步现象。前者５月底开始进入成熟期,后者７月初进入成熟期。初级卵母细胞由Ⅱ时相发育到Ⅳ时相基本上是同步的。第Ⅳ期卵巢卵径的频率仅出现１个高峰。养殖鲥鱼属１年１次产卵类型。     

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.     

Differentiation of the animal-vegetal axis in Xenopus laevis oocytes. I. Polarized intracellular translocation of platelets establishes the yolk gradient

The animal-vegetal axis of the oocyte of Xenopus laevis is recognizable not only by the pattern of surface pigmentation, but also by the distribution of yolk platelets, with the largest platelets (congruent to 14 microns in diameter) and 70% of the total yolk protein localized in the vegetal hemisphere. We have used fluorescent and radioactive vitellogenins (yolk protein precursors) to study the spatial and temporal patterns of yolk deposition along this axis. We find that the rate of uptake of vitellogenin is nearly uniform over the surface of vitellogenic oocytes of all sizes. Once formed, yolk platelets in the animal hemisphere move inward, around the germinal vesicle, and into the central region of the vegetal hemisphere. Yolk platelets of the vegetal hemisphere do not actively move but are slowly displaced from the surface by successive layers of younger platelets arising and enlarging near the surface. The oldest yolk platelets, which arise circumcortically at the beginning of vitellogenesis in stage II and III oocytes, eventually come to reside in the vegetal hemisphere of stage VI oocytes, in the upper portion of the cup-shaped region of largest platelets. The vegetal hemisphere thus gains the majority of yolk protein by directed intracellular transport from the animal hemisphere adding to the amount directly sequestered by the vegetal hemisphere.     

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.     

Nonreciprocal gonadal dysgenesis in hybrids of the chironomid midgeChironomus thummi. IV. Behavior of a female-specific protein,probably a vitellogenin

Using denaturing SDS-polyacrylamide gel electrophoresis, a protein with a subunit MW of about 148,000 daltons could be detected in the fat body of females of the reciprocal hybrids of Chironomus thummi thummi and Chironomus thummi piger, which is not present in males. This protein is presumably a vitellogenin and can be found in both hybrids during the late fourth-instar larval stage until eclosion of the adults, i.e., in early vitellogenesis. After eclosion, the reciprocal hybrids behave differently concerning the 148-kd protein. In females of the piger female x thummi male cross, which are fertile and produce yolky eggs, the 148-kd protein disappears from the fat body immediately after eclosion. In females of the reciprocal cross (thummi female x piger male) which are affected by gonadal dysgenesis and in which the oocytes only rarely contain yolk, the 148-kd protein is still present in the fat body of the adult up to 50 hr after eclosion until the fat body degrades. It is concluded that the inability of the sterile thummi female x piger male females to produce yolky eggs is caused by an impaired uptake of the presumed 148-kd vitellogenin into oocytes and not by a defective vitellogenesis. The impaired vitellogenin deposition into oocytes is taken as another aberrant trait of gonadal dysgenesis of the thummi female x piger male hybrids.     

Electron microscope studies on the origin and maturation of yolk in oocytes of the tunicate,Ciona intestinalis

Summary The origin of proteinaceous yolk in oocytes of Ciona, intestinalis appears to involve the activity of two kinds of vesicles derived from the Golgi complex. One kind of vesicle contains a granular product of considerable density while the contents of the other type of vesicle are of low density. Both types of vesicles become widely dispersed in the ooplasm during vitellogenesis. The high-density vesicle exhibits greater size variation than the lowdensity vesicle. The growing yolk globules possess an external often folded membrane enclosing both granular and vesicular elements. The granular-vesicular bodies are observed in wide size ranges and they appear to arise and increase in size by fusion or incorporation of numerous high-density vesicles, low-density vesicles, and smaller granular-vesicular bodies. The relationship of the developing yolk globules to ribosomes, pinocytotic vesicles, and vesicular endoplasmic reticulum is illustrated.This investigation was supported by research grants (GM-09229, HD-00699) from the National Instituts of Health, U. S. Public Health Service and a Career Development Award (GM-11,524) from the National Institute of General Medical Science.