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The ovaries of the largescale yellowfish, Labeobarbus marequensis (Teleostei: Cypriniformes: Cyprinidae), are made up of the germinal epithelium, nests of late chromatin nucleolus stage oocytes, and ovarian follicles. Each follicle is composed of a single oocyte, which is surrounded by somatic follicular cells and a basal lamina covered by thecal cells. We describe polarization and ultrastructure of oocytes during the primary growth stage. The oocyte nucleus contains lampbrush chromosomes, nuclear bodies and fibrillar material in which multiple nucleoli arise. Nuage aggregations composed of material of a nuclear origin are present in the perinuclear cytoplasm. The Balbiani body (Bb) contains aggregations of nuage, rough endoplasmic reticulum, individual mitochondria and complexes of mitochondria with nuage (cement). Some mitochondria in the Bb come into close contact with endoplasmic reticulum cisternae and vesicles that contain granular material. At the start of primary growth, the Bb is present in the cytoplasm close to the nucleus. Next, it expands towards the oocyte plasma membrane. In these oocytes, a spherical structure, the so-called yolk nucleus, arises in the Bb. It consists of granular nuage in which mitochondria and vesicles containing granular material are immersed. Later, the Bb becomes fragmented and a fully grown yolk nucleus is present in the vegetal region. It contains numerous threads composed of granular nuage, mitochondria, lysosome-like organelles and autophagosomes. We discuss the formation of autophagosomes in the cytoplasm of primary growth oocytes. During the final step of primary growth, the cortical alveoli arise in the cytoplasm and are distributed evenly. The eggshell is deposited on the external surface of the oocyte plasma membrane and is made up of two egg envelopes that are pierced by numerous pore canals. The external egg envelope is covered in protuberances. During primary growth no lipid droplets are synthesized or stored in the oocytes.

BACKGROUND Animal germ cells have specific organelles that are similar to ribonucleoprotein complex, called germ plasm, which is accumulated in eggs. Germ plasm is essential for inherited mechanism of germ line segregation in early embryogenesis. Sea urchins have early germ line segregation in early embryogenesis. Nevertheless, organization of germ plasm-related organelles and their molecular composition are still unclear. Another issue is whether maternally accumulated germ plasm exists in the sea urchin eggs. RESULTS I analyzed intracellular localization of germ plasm during oogenesis in sea urchin Strongylocentrotus intermedius by using morphological approach and immunocytochemical detection of Vasa, a germ plasm marker. All ovarian germ cells have germ plasm-related organelles in the form of germ granules, Balbiani bodies, and perinuclear nuage found previously in germ cells in other animals. Maternal germ plasm is accumulated in late oogenesis at the cell periphery. Cytoskeletal drug treatment showed an association of Vasa-positive granules with actin filaments in the egg cortex. CONCLUSIONS All female germ cells of sea urchins have germ plasm-related organelles. Eggs have a maternally accumulated germ plasm associated with cortical cytoskeleton. These findings correlate with early segregation of germ line in sea urchins.

Oocyte development has been divided into five stages in the zebrafish Brachydanio rerio, based on morphological criteria and on physiological and biochemical events. In stage I (primary growth stage), oocytes reside in nests with other oocytes (Stage IA) and then within a definitive follicle (Stage IB), where they greatly increase in size. In stage II (cortical alveolus stage), oocytes are distinguished by the appearance of variably sized cortical alveoli and the vitelline envelope becomes prominent. In stage III (vitellogenesis), yolk proteins appear in oocytes and yolk bodies with crystalline yolk accrue during this major growth stage. Ooctes develop the capacity to respond in vitro to the steroid 17α, 20β-dihydroxy-4-pregnen-3-one (DHP) by undergoing oocyte maturation. In stage IV (oocyte maturation), oocytes increase slightly in size, become translucent, and their yolk becomes non-crystalline as they undergo final meiotic maturation in vivo (and in response to DHP in vitro). In stage V (mature egg), eggs (approx. 0.75 mm) are ovulated into the ovarian lumen and are capable of fertilization. This staging series lays the foundation for future studies on the cellular processes occurring during oocyte development in zebrafish and should be useful for experimentation that requires an understanding of stage-specific events. © 1993 Wiley-Liss, Inc.

Germ cells of the chick ovary which develop asymmetrically on the right and left sides of the embryo were observed by electron microscopy from 7 to 17 days of incubation. Germ cells showed different patterns in the right and left ovaries, and also differences in the cortex and in the medulla. At 7 to 9 days, germ cells were individually present in both the right and left ovaries. They proliferated from 10 days onward and formed many cell aggregates. In each aggregate, germ cells were joined by intercellular bridges, and their cell cycles were synchronized. Although meiotic features of the germ cells were frequently found in the cortex of the left ovaries at 16 days, some germ cells exhibited these features at earlier days. In the meiotic germ cells, the "Balbiani body," which was composed of a concentration of cell organelles shifted to one pole of the cell, was always seen. The appearance of a meiotic nucleus and Balbiani body was characteristic of germ cells located in the left ovarian cortex, whereas those were never seen in the left medulla and in the right ovary. At 16 and 17 days, some germ cells were released into the lacunae of the medulla of both the right and left ovaries. The meaning of this phenomenon is discussed. Degenerating germ cells were frequently observed in the right ovary, but rarely in the left.

(1) In an animal where the corpus allatum complex is inhibited by glucose feeding, the ovariole develops to a certain size without yolk deposition in the oocytes. Histologically this can be registered as: (a) Lipid spheres are found in the young oocytes in the vicinity of the Balbiani body (as in young normal oocytes). However, this lipid decreases in amount and "new" lipid (from the fat body via haemolymph) is not deposited in the later oocytes. (b) No carbohydrate/protein yolk is formed. (c) Glycogen is not synthesized in the oocytes. (d) The follicle cells aggregate glycogen instead of lipid. (e) No qualitative differences have been observed regarding the contributions from the tropharium (the so-called Type 1 vacuole, ribosomes, mitochondria, annulated lamellae: Schreiner, '77). (2) Implantation of a corpus allatum complex results in deposition of lipid, carbohydrate/protein and glycogen yolk. However, the restoration period differs histologically from the normal development as: (a) Glycogen appears in the oocyte earlier than normal, i.e., at Stage 4, while normally at Stage 6'. (b) Glycogen appears in the nutritive tube adjacent to the interfollicular plug cells. (c) Both the inner and outer layer of the ovariole sheath contain glycogen, the outer layer contains lipid spheres as well.

Oogenesis in the anuran Xenopus laevis can be divided into six stages based on the anatomy of the developing oocyte. Stage I consists of small (50 to 100 μ) colorless oocytes whose cytoplasm is transparent. Their large nuclei and mitochondrial masses are clearly visible in the intact oocyte. Stage II oocytes range up to 450 μ in diameter, and appear white and opaque. Stage I and II are both previtellogenic. Pigment synthesis and yolk accumulation (vitellogenesis) begins during Stage III. Vitellogenesis continues through Stage IV (600 to 1000 μ), the oocytes grow rapidly, and the animal and vegetal hemispheres become differentiated. By Stage V (1000 to 1200 μ) the oocytes have nearly reached their maximum size and yolk accumulation gradually ceases. Stage VI oocytes are characterized by the appearance of an essentially unpigmented equatorial band. They range in size from 1200 to 1300 μ, are postivtellogenic and ready for ovulation. These stages of oocyte development have been correlated with physiological and biochemical data related to oogenesis in Xenopus.

The ultrastructural details of human oocytes from four primordial follicles and one early primary follicle are presented. A fifth primordial follicle is represented by a paraffin section stained by hematoxylin and eosin. The paranuclear Balbiani vitelline body, contsisting of a centrosome surrounded by endoplasmic reticulum, Golgi complexes, compound aggregates, annulate lamellae, and mitochondria is described. The annulate lamellae arise as an evagination from the outer leaflet of the nuclear envelope and interdigitate with folds of the endoplasmic reticulum which also is continuous with the outer leaflet of the nuclear envelope. Structural aspects of annulate lamellae are discussed in relationship to current ideas of nuclear membrane ultrastructure and to their possible role in nucleo-cytoplasmic transfer. A biographical note on the life of Edouard Gerard Balbiani is presented.

During oogenesis in Pentastomida the oocytes wander from a germinal zone in the mid-dorsal ovarial wall to the lateral pouches of the ovary. The growth phases are initiated during that migration, but not until the lateral pouches are reached does the oocyte grow considerably. A Balbiani body consisting of numerous mitochondria, and various vacuolar inclusions are formed, and at the same time the oocyte bulges out into the hemocoel. Some wall cells form a stalk and cover part of the oocyte towards the hemocoel. During later stages of oocyte growth they withdraw, and the oocyte is separated from the hemocoel only by an extremely thin basement membrane. It seems that the young oocytes obtain nourishment from the ovarial lumen by way of the wall cells. The contents of the lumen in its turn seems to be derived from the hemocoel through the activity of mid-ventral secretory cells. The older oocytes are provided with numerous microvilli, and material for the growth of the oocytes must be taken up directly from the hemocoel. A very dense egg shell is secreted by the oocyte. In nearly mature oocytes the microvilli withdraw from penetrating this shell, and a mucopolysaccharide layer is formed beneath the shell. The mature oocytes in some unknown way make their way to the ovarial lumen whence they are transported to the uterus.