Preparation of mammalian oocytes for transmission electron microscopy

Cellular and molecular alterations of buffalo oocytes cultured under two different levels of oxygen tension during in vitro maturation

This study was conducted to monitor the cellular and molecular changes of buffalo cumulus-oocytes complexes (COCs) cultured under high or low oxygen levels. Morphologically good quality COCs (n = 1627) were screened using brilliant cresyl blue (BCB) staining and placed into three groups (BCB+, BCB- and control). All groups of COCs were cultured under low (5%) or high (20%) oxygen tensions. Intracellular and molecular changes including oocyte ultrastructure, lipid contents, mitochondrial activity and transcript abundance of genes regulating different pathways were analyzed in the matured oocyte groups. The results revealed that oxygen tension did not affect cumulus expansion rates, however the BCB+ group had a higher (P ≤ 0.05) expansion rate compared with the BCB- group. BCB- oocytes recorded the lowest meiotic progression rate (P ≤ 0.05) under high oxygen levels that was linked with an increased level of reactive oxygen species (ROS) compared with the BCB+ oocytes. Ultrastructure examination indicated that BCB+ oocytes had a higher rate of cortical granules migration compared with BCB- under low oxygen tension. In parallel, our results indicated the upregulation of NFE2L2 in groups of oocytes cultured under high oxygen tension that was coupled with reduced mitochondrial activity. In contrast, the expression levels of MAPK14 and CPT2 genes were increased (P ≤ 0.05) in groups of oocytes cultured under low compared with high oxygen tension that was subsequently associated with increased mitochondrial activity. In conclusion, data from the present investigation indicated that low oxygen tension is a favourable condition for maintaining the mitochondrial activity required for nuclear maturation of buffalo oocytes. However, low-quality oocytes (BCB-) responded negatively to high oxygen tension by reducing the expression of gene-regulating metabolic activity (CPT2). This action was an attempt by BCB- oocytes to reduce the increased levels of endogenously produced ROS that was coupled with decreased expression of the gene controlling meiotic progression (MAPK14) in addition to nuclear maturation rate.

Investigating the mechanical properties of zona pellucida of whole human oocytes by atomic force spectroscopy

The role of mechanics in numerous biological processes is nowadays recognized, while in others, such as the fertilization process, it is still neglected. In the case of oocytes the description of their mechanical properties could improve the comprehension of the oocyte-spermatozoon interaction and be helpful for application in in vitro fertilization (IVF) clinics. Herein the mechanical properties of whole human oocytes (HOs) immediately after retrieval are investigated by indentation measurements with atomic force spectroscopy under physiological conditions. Measurements are performed on immature (metaphase I - MI) and mature (metaphase II - MII) HOs. According to their morphological characteristics MII-HOs are classified as "suitable" and "rejected"; these latter would be usually rejected for intracytoplasmic sperm injection (ICSI). For all maturation stages we observe that the elastic response of the zona pellucida (ZP) outer layer was different and distinguishable from the rest of the ZP-HO. The elasticity of this ZP outer layer varies with maturation and quality: stiffness decreases from immature MI to good quality MII, up to poor-quality rejected MII. An indirect analysis with IVF outcome indicates that the ZP outer layer of analysed HOs donated by women who achieved pregnancy is stiffer than that of HOs from women with negative outcome. Our findings suggest that mechanical properties can represent important oocyte quality indicators that may be exploited for the design of innovative ICSI dedicated cell sorters.

Establishment and characterization of an air-liquid canine corneal organ culture model to study acute herpes keratitis

Despite the clinical importance of herpes simplex virus (HSV)-induced ocular disease, the underlying pathophysiology of the disease remains poorly understood, in part due to the lack of adequate virus-natural-host models in which to study the cellular and viral factors involved in acute corneal infection. We developed an air-liquid canine corneal organ culture model and evaluated its susceptibility to canine herpesvirus type 1 (CHV-1) in order to study ocular herpes in a physiologically relevant natural host model. Canine corneas were maintained in culture at an air-liquid interface for up to 25 days, and no degenerative changes were observed in the corneal epithelium during cultivation using histology for morphometric analyses, terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling (TUNEL) assays, and transmission electron microscopy (TEM). Next, canine corneas were inoculated with CHV-1 for 48 h, and at that time point postinfection, viral plaques could be visualized in the corneal epithelium and viral DNA copies were detected in both the infected corneas and culture supernatants. In addition, we found that canine corneas produced proinflammatory cytokines in response to CHV-1 infection similarly to what has been described for HSV-1. This emphasizes the value of our model as a virus-natural-host model to study ocular herpesvirus infections.

IMPORTANCE

This study is the first to describe the establishment of an air-liquid canine corneal organ culture model as a useful model to study ocular herpesvirus infections. The advantages of this physiologically relevant model include the fact that (i) it provides a system in which ocular herpes can be studied in a virus-natural-host setting and (ii) it reduces the number of experimental animals needed. In addition, this long-term explant culture model may also facilitate research in other fields where noninfectious and infectious ocular diseases of dogs and humans are being studied.