Cytochemical characterization of the endomembranous system during oocyte secondary growth in Serrasalmus spilopleura (Teleostei, Characiformes, Characidae)

Microscopic study of the primary growth ovarian follicles of the pike-perch Sander lucioperca (Linnaeus 1758) (Actinopterygii, Perciformes)

The ovaries of Sander lucioperca (Actinopterygii, Perciformes) are made up of the germinal epithelium and ovarian follicles, in which primary oocytes grow. Each follicle is composed of an oocyte surrounded by flattened follicular cells, the basal lamina, and thecal cells. The early stages of oocyte development (primary growth = previtellogenesis) are not fully explained in this species. The results of research with the use of stereoscopic, light, fluorescence, and transmission electron microscopes on ovarian follicles containing developing primary oocytes of S. lucioperca are presented. The polarization and ultrastructure of oocytes are described and discussed. The deposition of egg envelopes during the primary growth and the ultrastructure of the eggshell in maturing follicles of S. lucioperca are also presented. Nuclei in primary oocytes comprise lampbrush chromosomes, nuclear bodies, and nucleoli. Numerous additional nucleoli arise in the nucleoplasm during primary growth and locate close to the nuclear envelope. The Balbiani body in the cytoplasm of oocytes (ooplasm) is composed of nuage aggregations of nuclear origin and mitochondria, endoplasmic reticulum (ER), and Golgi apparatus. The presence of the Balbiani body was reported in oocytes of numerous species of Actinopterygii; however, its ultrastructure was investigated in a limited number of species. In primary oocytes of S. lucioperca, the Balbiani body is initially located in the perinuclear ooplasm on one side of the nucleus. Next, it surrounds the nucleus, expands toward the plasma membrane of oocytes (oolemma), and becomes fragmented. Within the Balbiani body, the granular nuage condenses in the form of threads, locates near the oolemma, at the vegetal oocyte pole, and then dissolves. Mitochondria and cisternae of the rough endoplasmic reticulum (RER) are present between the threads. During primary growth micropylar cells differentiate in the follicular epithelium. They contain cisternae and vesicles of the RER and Golgi apparatus as well as numerous dense vesicles suggesting high synthetic and secretory activity. During the final step of primary growth several follicular cells delaminate from the follicular epithelium, migrate toward the oocyte and submerge in the most external egg envelope. In the ooplasm, three regions are distinguished: perinuclear, endoplasm, and periplasm. Cortical alveoli arise in the perinuclear ooplasm and in the endoplasm as a result of the fusion of RER vesicles with Golgi ones. They are evenly distributed. Lamellar bodies in the periplasm store the plasma membrane and release it into a space between the follicular cells and the oocyte. The developing eggshell in this space is made up of two egg envelopes (the internal one and the external) that are pierced by canals formed around the microvilli of oocytes and the processes of follicular cells. In the deposition of egg envelopes the oocyte itself and follicular cells are engaged. In maturing ovarian follicles the eggshell is solid and the internal egg envelope is covered with protuberances.

Asymmetry in the cytoplasm of oocytes of largescale yellowfish Labeobarbus marequensis Smith 1841 (Teleostei: Cypriniformes: Cyprinidae)

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.

Acid and alkaline phosphatase localization in the digestive tract mucosa of the Hemisorubim platyrhynchos

This cytochemical study investigated the acid and alkaline phosphatase of the digestive tract of Hemisorubim platyrhynchos. Acid phosphatase was detected in the lining epithelium throughout the digestive tract, whereas alkaline phosphatase was only observed in the intestine. In the esophagus, an acid phosphatase reaction occurred in the apical cytoplasm of the epithelial cells and was related to epithelial protection and freeing of superficial cells for sloughing. Similar results were also observed in epithelial cells of gastric epithelium. In the gastric glands, acid phosphatase occurred in lysosomes of the oxynticopeptic cells acting in the macromolecule degradation for use as an energy source, whereas in the vesiculotubular system, its presence could be related to secretion processes. Furthermore, acid phosphatase in the intestine occurred in microvilli and lysosomes of the enterocytes and was correlated to absorption and intracellular digestion. However, no difference was reported among the regions of the intestine. However, alkaline phosphatase reaction revealed a large number of reaction dots in the anterior intestine, with the number decreasing toward the posterior intestine. This enzyme has been related to several functions, highlighting its role in the nutrient absorption primarily in the anterior intestine but also being essential in pH regulation because this is a carnivorous species with many gastric glands with secretions that could damage the intestine.

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.