Acrosome reaction in spermatozoa from hagfish (Agnatha) Eptatretus burgeri and Eptatretus stouti: acrosomal exocytosis and identification of filamentous actin

A Review on Environmental Contaminants-Related Fertility Threat in Male Fishes: Effects and Possible Mechanisms of Action Learned from Wildlife and Laboratory Studies

Increasing global rates of diminished fertility in males has been suggested to be associated with exposure to environmental contaminants (ECs). The aquatic environments are the final repository of ECs. As the reproductive system is conserved in vertebrates, studies on the effects of ECs on fertility endpoints in fishes provide us with valuable information to establish biomarkers in risk assessment of ECs, and to understand the ECs-related fertility threat. The aim of the present review was to evaluate associations between ECs and fertility determinants to better understand ECs-related male fertility threat in male fishes. Wildlife studies show that the reproductive system has been affected in fishes sampled from the polluted aquatic environment. The laboratory studies show the potency of ECs including natural and synthetic hormones, alkylphenols, bisphenols, plasticizers, pesticides, pharmaceutical, alkylating, and organotin agents to affect fertility determinants, resulting in diminished fertility at environmentally relevant concentrations. Both wildlife and laboratory studies reveal that ECs adverse effects on male fertility are associated with a decrease in sperm production, damage to sperm morphology, alternations in sperm genome, and decrease in sperm motility kinetics. The efficiency of ECs to affect sperm quality and male fertility highly depends on the concentration of the contaminants and the duration of exposure. Our review highlights that the number of contaminants examined over fertility tests are much lower than the number of contaminants detected in our environment. The ECs effects on fertility are largely unknown when fishes are exposed to the contaminants at early developmental stages. The review suggests the urgent need to examine ECs effects on male fertility when a fish is exposed at different developmental stages in a single or combination protocol. The ECs effects on the sperm genome are largely unknown to understand ECs-related inheritance of reproductive disorders transmitted to the progeny. To elucidate modes of action of ECs on sperm motility, it is needed to study functional morphology of the motility apparatus and to investigate ECs-disrupted motility signaling.

Sperm acrosome reaction: its site and role in fertilization

Manner and roles of sperm acrosome reaction in a variety of animals were compared.

Stimulation of regulatory volume increase (RVI) in avian articular chondrocytes by gadolinium chloride

Chondrocytes, the resident cell-type of articular cartilage, are responsible for the regulation of the extracellular matrix (ECM) in response to their physico-chemical environment. Due to the nature of cartilage loading, chondrocytes are exposed to constant changes in extracellular osmolality with a gradual increase throughout the day. As an increase in osmolality attenuates matrix synthesis, we have studied cell volume regulation (regulatory volume increase (RVI)) after hypertonic challenge and the regulation of RVI by the actin cytoskeleton. Using freshly isolated avian articular chondrocytes, changes in actin organisation were studied by confocal laser scanning microscopy following a 43% increase in extracellular osmolality. Using calcein-loading chondrocytes, the capacity for RVI was determined and the rate of volume recovery (t1/2) mathematically extrapolated. Following an increase in extracellular osmolality there was a significant increase (p < 0.05) in cortical actin, inhibited by the removal of extracellular calcium EGTA or by the addition of 100 µmol·L–1 gadolinium chloride. Most cells exhibited slow RVI (t1/2 = 55.5 ± 5.5 min), whereby inhibition of actin polymerisation by gadolinium chloride or the removal of extracellular calcium significantly increased the rate of volume recovery via a bumetanide-sensitive pathway (t1/2 of 29.6 ± 6.5 min and 13.8 ± 3.1 min, respectively). These data suggest the Na+–K+–2Cl– (NKCC) co-transporter regulated by the actin cytoskeleton is involved in avian chondrocyte RVI.

Ultrastructural study on the fertilisation process in sturgeon (Acipenser), function of acrosome and prevention of polyspermy

Sturgeon gametes differ from other fish in that their spermatozoa possess acrosome with finger-like posterolateral projections, which undergo exocytosis and filament formation, whereas eggs possess numerous micropyles. The fertilisation process in Acipenser baerii was investigated by fluorescence and electron microscopy. A suitable activation solution containing 2.5 mM CaCl(2), 15 mM Tris, pH 10 was found for detailed description of acrosomal reaction. The acrosome reaction includes the formation of a spear-like fertilisation filament coming from three endonuclear canals and implantation fossa through the acrosomes. It can accelerate the process of polyspermy prevention. Another unique feature of the acrosome was an anchor-like opening of the posterolateral projections. Mature eggs of A. baerii possessed 2-10 micropyles in the animal pole region. The eggs consisted of three principal layers and an outermost jelly coat blocking micropyle, and a layer of cortical granules in unfertilised eggs. With the exposure to freshwater, the jelly like layer separated from the egg surface, whereas the cortical granules swelled. No change between the layers of fertilised and unfertilised eggs, apart from the generation of an increasing perivitelline space by dissolution of the cortical granules, had been observed after the fusion of spermatozoon with an egg. A fertilisation cone blocked a fusion of other spermatozoa with cytoplasmatic projection in the fertilised micropyle.

The optimization of the protocol for immunofluorescence on fish spermatozoa

In comparison with mammals, the fertilization of fish occurs predominantly outside the organism in a water environment, where fish spermatozoa require specific conditions to interact with oocytes. It is evident that optimal conditions for fish and mammalian spermatozoa are quite different. This paper describes a special approach to handling fish (common carp and Siberian sturgeon) spermatozoa in comparison with the samples originating from mammals (boar). This approach concerns not only the differences in the composition of the media applied but also primarily emphasizes the concrete parts of the immunofluorescence protocol determining accurate results. Individual parts of the protocol for indirect immunofluorescence of mammalian sperm were changed step by step and modified protocols were applied to immunofluorescence experiments with carp and sturgeon spermatozoa. By evaluating the changes in the integrity of the fish sperm head and flagellum, we selected the steps and corresponding conditions that are crucial for handling the fish spermatozoa. Based on our results, it may be concluded that when working with fish spermatozoa, the cells attached to the microscopic slides must not desiccate prior to the fixation, which is a usual step when working with mammalian sperm. The second crucial step is the necessity to fix the fish spermatozoa, especially when the research is focused on the structure of the flagellum. The impact of the temperature conditions is rather low, but working at low temperatures, except for the period of incubation with antibodies, leads to a higher number of unaffected cells.

Spermiogenesis in the Hagfish Eptatretus burgeri (Agnatha)

The fine structure of spermatid differentiation in a primitive vertebrate, the hagfish, whose spermatozoa bear acrosomes, was investigated. In early round spermatids, the acrosomal vesicles were spherical and located in a shallow nuclear indentation, flanked by the plasma and the nuclear membranes. The vesicle underwent a transition through lens-shaped and cap-shaped stages until it attained the shape of a bell in mature spermatozoa. Electron-dense acrosomal material that appeared as deposits in three portions of the vesicle finally joined in the center region at a late stage. Condensation of chromatin occurred in the anterior region of the nucleus. During transformation of the spermatids, many regularly spaced microtubules appeared beneath the plasma membrane except in the anteriormost region of the cell. The microtubules in a single alignment lay parallel to one another and encased the nucleus diagonally. During an early stage, the centrioles changed their orientation from perpendicular to longitudinal and rotated to become parallel to the long axis of the nucleus. Thus, the flagellum lay nearly straight along the cell axis. A cytoplasmic canal appeared transiently during the early stage. A droplet of cytoplasm was eliminated after descending along the flagella. The features of spermiogenesis in hagfish, which lies between invertebrates and vertebrates, are compared with those of other animals.

Acrosome Reaction in Spermatozoa from the Amphioxus Acrosome Reaction in Branchiostoma belcheri (Cephalochordata, Chordata)

The formation of an acrosomal process at acrosomal exocytosis in spermatozoa of the amphioxus was described in the present report for the first time. A non-reacted acrosome was located in front of the nucleus, where a cup-shaped acrosomal vesicle covered a conical accumulation of subacrosomal material. When naturally spawned spermatozoa were treated with a calcium ionophore, ionomycin, the acrosomal vesicle opened at the apex and an acrosomal process was projected. The process exhibited a filamentous structure. The reaction followed the mode typically seen in marine invertebrates. These observations suggest that the features and function of the acrosome of amphioxus, whose position is on the border between invertebrates and vertebrates, reflect their ecological adaptation and phylogenic position.