DNA and RNA pattern of staining during oogenesis in zebrafish (Danio rerio): a confocal microscopy study

Silver Nanoparticle-Induced Nephrotoxicity in Zebrafish (Danio rerio)

The escalating challenge of antibacterial resistance has driven the widespread use of silver nanoparticles (AgNPs) due to their potent antimicrobial properties. AgNPs can be synthesised through diverse methods, spanning conventional chemical and physical routes to the increasingly favoured biosynthesis approach. While offering environmental advantages, the ecological impact of biogenically synthesized AgNPs, especially on aquatic ecosystems, requires thorough evaluation. The renal system, critical for maintaining physiological homeostasis via nephron-mediated waste removal, fluid regulation, and electrolyte balance, is highly vulnerable to toxicant-induced damage, which can negatively affect organismal fitness. This study aimed to assess the nephrotoxic effects of AgNPs, synthesized using entirely "green" methods, on zebrafish after 96-h exposures to three distinct concentrations alongside a control group. Acridine orange fluorescence microscopy revealed dose-dependent histopathological alterations in renal tissues. Specifically, at 0.031 μg/L and 0.250 μg/L, significant changes were observed, including glomerular shrinkage, proliferation of hematopoietic tissue, dissociation and dilation of renal tubules, and melanomacrophage aggregation. At 5.000 μg/L, prolonged exposure beyond 48 h indicated a potential for renal tissue cell renewal, suggesting a possible compensatory response. These results demonstrate the sensitivity of zebrafish kidneys to AgNPs and emphasize the imperative for comprehensive in vivo toxicity testing, irrespective of synthesis method, to accurately evaluate the potential for adverse ecological impacts and ensure the preservation of aquatic ecosystem integrity.

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.

Morphological and molecular effects of cortisol and ACTH on zebrafish stage I and II follicles

Oogenesis in zebrafish (Danio rerio) is controlled by the hypothalamus-pituitary-gonadal axis and reproductive hormones. In addition, an interference of stress hormones is known with reproductive biology. In the presented work, we aimed to explore the hypothesis that cortisol (Cort) and ACTH may affect early oogenesis in zebrafish, given the presence of the specific receptors for glucocorticoids and ACTH in the zebrafish ovary. Follicles at stages I and II were exposed in vitro to 1  μM Cort and ACTH for 48 h, then ultrastructural and molecular effects were analyzed. The comet assay demonstrated increased tail moments for Cort and ACTH treatment indicative of DNA damage. The mRNA expression of apoptotic genes (bax, bcl-2) was not altered by both treatments, but Cort increased significantly the expression of the ACTH receptor (mc2r). Cort stimulated the presence of the endoplasmic reticulum, predominantly at stage II, while ACTH induced a strong vacuolization. Viability of oocytes was not affected by both treatments and fluorescent staining (monodansylcadaverine/acridine orange) indicated a reduced quantity of autophagosomes for ACTH, and lower presence of nucleic acids in ooplasm for Cort and ACTH. Concluding, different responses were observed for stress hormones on early stages of zebrafish oocytes, which suggest a role for both hormones in the stress-mediated adverse effects on female gametogenesis.

Gross morphological features of the organ surface primo-vascular system revealed by hemacolor staining

The primo-vascular system (PVS), which consists of primo-vessels (PVs) and primo-nodes (PNs), is a novel thread-like structure identified in many animal species. Various observational methods have been used to clarify its anatomical properties. Here, we used Hemacolor staining to examine the gross morphology of organ-surface PVS in rats. We observed a sinus structure (20-50  μ m) with a remarkably low cellularity within PNs and PVs and several lines of ductules (3-5  μ m) filled with single cells or granules (~1  μ m) in PV. Both sinuses and ductules were linearly aligned along the longitudinal axis of the PVS. Such morphology of the PVS was further confirmed by acridine orange staining. In PN slices, there was a honeycomb-like structure containing the granules with pentagonal lumens (~10  μ m). Both PVs and PNs were densely filled with WBCs, RBCs, and putative mast cells (MCs), which were 90.3%, 5.9%, and 3.8% of the cell population, respectively. Granules in putative MCs showed spontaneous vibrating movements. In conclusion, the results show that Hemacolor, a simple and rapid staining system, can reveal the gross morphological features reported previously. Our findings may help to elucidate the structure and function of the PVS in normal and disease states in future studies.