Elektrophoretische Untersuchungen zur Vitellogenese vonBrachydanio rerio (Cyprinidae, Teleostei)

Vitellogenin cleavage products as indicators for toxic stress in zebra fish embryos: a proteomic approach

Vitellogenins (Vtgs) are the major yolk proteins in all oviparous animals. Systematic and regulated processing of these during embryogenesis is crucial for embryonic development. In the present study, toxicant-induced disturbance of Vtg degradation processes during Danio rerio (DR) embryogenesis was analysed to establish a sensitive tool for monitoring toxic stress at the molecular level. A 2-DE-based proteomic approach for whole DR embryos was established to study Vtg cleavage products (lipovitellin (Lv) derivatives). Ethanol was chosen as a positive control for a toxicity related change in the proteome of whole zebra fish embryos. Protein extracts from embryos treated with two ethanol concentrations, 0.5 and 2% v/v, showing either no or very strong visible effects, like absent heartbeat and blood circulation, were examined. Significant changes in the Lv pattern were detected for both conditions. The results are interpreted as scope for the use of the high abundant Lv derivatives as sensitive stress indicators in zebra fish embryos reflecting the overall fitness of the intact organisms.

Comparison of vitellogenin responses in zebrafish and rainbow trout following exposure to environmental estrogens

In this comparative study, the suitability of the commonly used in vivo biomarker for estrogenicity, vitellogenin (VTG), upon waterborne exposure to known environmental estrogens is evaluated in both male zebrafish (Danio rerio) and juvenile rainbow trout (Oncorhynchus mykiss). The results from initial experiments in which both species were exposed to 4-tert-octylphenol (OP) or 17 alpha-ethynylestradiol under semistatic conditions for 3 weeks demonstrated a difference in species sensitivity for OP exposure. Additional dose-response studies (semistatic, 3 weeks) with 4-nonylphenol (20, 100, and 500 microg/L), bisphenol A (40, 200, and 1000 microg/L), dibutylphthalate (40, 200, and 1000 microg/L DBP), and 17beta-estradiol (20 and 100 ng/L E2) were conducted. All these compounds, except for DBP, were found to be estrogenic to both fish species. The results demonstrated a difference in species sensitivity for NP with the zebrafish being about 5 times less sensitive. For the other compounds tested, no indications for a difference in species sensitivity was found. The results from this study demonstrated that both fish species can be used for the detection of VTG as biomarker for estrogenicity, taken into the potential interspecies differences in sensitivity which might be important for the evaluation of fish population effects.

Ultrastructural aspects of oogenesis and oocyte growth in fish and amphibians

Oogenesis, the early events of primary oocyte growth (meiotic arrest, synapsis, ribosomal gene duplication), and folliculogenesis can be seen to particular advantage in the germinal ridge of the syngnathan ovary. After budding off the germinal ridge (a compartment of the luminal epithelium), nascent follicles then enter into a linear array of developing follicles within which temporal and stage-specific events can be correlated with spatial distribution. Prominent features of the later phase of primary oocyte growth include intense transcriptional activity and the formation and subsequent dispersal of the Balbiani vitelline body (mitochondrial cloud) concomitant with an increase in cytoplasmic organelles and volume. Further oocyte growth is characterized by a period of cortical alveolus (in teleosts) or cortical granule (in anurans) formation, in which Golgi elements play a predominant role, and finally vitellogenesis. The latter process, which is responsible for the preponderance of oocyte growth, includes the hepatic synthesis and secretion of vitellogenin (VTG), the uptake of VTG from the bloodstream into the oocyte by receptor-mediated endocytosis, and the transport of VTG via endosomes and multivesicular bodies to forming yolk platelets. In the process, VTG is proteolytically cleaved into the yolk proteins, which assume either a monoclinic (in cyclostomes) or orthorhombic (in teleosts and amphibians) crystalline array. Other structures associated with the growing oocyte are also briefly discussed, including nuage, the vitelline envelope, intercellular junctions between the oocyte and overlying follicle cells, pigment, intramitochondrial crystals in ranidae, and annulate lamellae.

Oogenesis in Fundulus heteroclitus. III. Vitellogenesis

Several physiological parameters associated with oocyte growth (vitellogenesis) in the killifish, Fundulus heteroclitus, are defined. Hepatocytes from females and estrogen-treated males are highly synthetic cells, whereas those from males are relatively quiescent. A 2000,000-molecular weight phosphoprotein (vitellogenin) has been identified by sodium dodecyl sulfate (SDS)-gel electrophoresis in the plasma of females and estrogen-treated males and isolated chromatographically using a potassium phosphate gradient system on DEAE-cellulose. To inhibit proteolysis, the nontoxic inhibitor, aprotinin, was injected into fish prior to bleeding. The structure of vitellogenic follicles and the process of oocyte growth are described. Once follicles reach a diameter of 0.5 mm, their oocytes incorporate exogenous materials by micropinocytosis and sequestered material is immediately translocated to yolk spheres in the oocyte cortex. This process has been followed by using the tracer horseradish peroxidase. Exogenous proteins appear to leave the perifollicular capillaries via an intercellular route and pass through intercellular channels within the follicular epithelium and patent pore canals of the vitelline envelope before reaching the oocyte surface. [32P]Vitellogenin isolated from F. heteroclitus, [3H]vitellogenin isolated from X. laevis, and the dye trypan blue have been used to determine which sized follicles are vitellogenic (i.e., incorporate exogenous materials into growing oocytes). Morphological and autoradiographic studies are presented to confirm that sequestered macromolecules are incorporated into yolk spheres in the growing oocyte. Follicles appear to grow from 0.5 to 1.3 mm in diameter due to vitellogenesis and subsequently undergo an additional increase in size, which is primarily due to hydration, during oocyte maturation (Wallace and Selman, '78).

Oocyte growth in the sheepshead minnow: uptake of exogenous proteins by vitellogenic oocytes

The structure of the vitellogenic follicles of the sheepshead minnow, Cyprinodon variegatus, is described. Follicles enlarge primarily by protein yolk accumulation (vitellogenesis) and subsequently increase in size by hydration. This study uses the electron-dense tracer, horseradish peroxidase, and a larger heterologous protein, Xenopus laevis [3H]vitellogenin, to follow the fate of exogenous proteins from the maternal circulation to yolk spheres of the growing oocyte. Materials appear to leave the perifollicular capillaries via an interendothelial route, traverse the theca and the patent intercellular channels of the follicular epithelium and the pore canals of the vitelline envelope. At the oocyte surface they are incorporated via micropinocytosis and translocated to growing yolk spheres in the peripheral ooplasm. In contrast to other studies on oocyte growth in teleosts which suggest that yolk is an autosynthetic product, this study substantiates the importance of heterosynthetic processes during oocyte growth in C. variegatus.