Biophysics of Fish Sperm Flagellar Movement: Present Knowledge and Original Directions

A fish spermatozoon has a minimalist structure: head, mid-piece and flagellum with the active inner core, called “axoneme”. The axoneme represents a cylindrical scaffold of microtubular doublets arranged around a pair of single microtubules and assorted along the entire length with the dynein-ATPase motors. The mechanisms of wave generation along the flagellum becomes possible due to sliding of microtubules relative to each other and their propagation is a result of a balance between mechanical constraints and intra-flagellar biochemical actors that generate force

Fish Sperm Physiology: Structure, Factors Regulating Motility, and Motility Evaluation

For reproduction, most fish species adopt external fertilization: their spermatozoa are delivered in the external milieu (marine- or freshwater) that represents both a drastic environment and a source of signals that control the motility function. This chapter is an updated overview of the signaling pathways going from external signals such as osmolarity and ionic concentration and their membrane reception to their transduction through the membrane and their final reception at the flagellar axoneme level. Additional factors such as energy management will be addressed as they constitute a limiting factor of the motility period of fish spermatozoa. Modern technologies used nowadays for quantitative description of fish sperm flagella in movement will be briefly described as they are more and more needed for prediction of the quality of sperm used for artificial propagation of many fish species used in aquaculture. The chapter will present some applications of these technologies and the information to which they allow access in some aquaculture species

Spermatozoidi riba, fizička i bioenergetske interakcije sa okolnom sredinom

Kod riba sa spoljašnjim oplođenjem, spermatozoidi se prilikom mresta isporučuju rastvoreni u pratećoj semenoj tečnosti u neposrednu okolinu gde se trenutno aktiviraju pokretima bičeva i na taj način stupaju u različite fizičke interakcije. Prvo se javlja osmotski signal na membrani spermatozoida i odmah zatim se talasi prenose sa vrha ka kraju duž biča oblika pantljike/trake (umesto cilindričnog oblika kod većine vrsta), što poboljšava efikasnost kretanje unapred. Zatim, zbog prisustva ovih “peraja” na bičevima, odnos površine i zapremine ribljih spermatozoida je mnogo veći nego kod većine drugih vrsta. Ovo vodi do bolje i brže trans membranske razmene, bilo da se radi o osmotskom, jonskom, gasovitom (CO2) ili vodenom transferu. Treće, fizička veza između bičeva i površina sa kojim oni reaguju (na primer staklo za slajdove mikroskopa) dovodi do značajnog poboljšanja njihovih pokreta dok plivaju u blizini ovakvih povrsina (kao sto je ljuska jajeta). Što se tiče bioenergetskih aspekata, spermatozoidi riba brzo plivaju dostižući veoma visoku frekvenciju udarca biča (do 70 - 100 Hz), što podrazumeva veliku potrošnju zaliha ATP-a. Njihova stopa respiracije i proizvodnje ATP-a u mitohondrijama je previše niska u poređenju sa potrošnjom ATP-a neophodnom za pokrete bičeva, odnosno njihovih dineinskih molekula u sklopu aksoneme bičeva. Kao posledica ovoga, intraćelijski nivo ATP-a se smanjuje u toku kretanja što prevremeno narušava pokretljivost ali takođe i druge funkcije kao sto je rad jonske i vodene pumpe. Ubrzo posle (od jednog do nekoliko minuta) aktivacije, nedostatak ATP-a je toliki da pokretljivost bičeva prestaje u potpunosti. Tok ovakvog procesa se moze preokrenuti, pošto se pokazalo da se zalihe ATP-a mogu nadoknaditi u uslovimu u kojima se sprečava pokretljivost spermatozoida, što otvara mogućnost za drugu rundu pokretljivosti. U ovoj prezentaciji prikazane su specifične odlike ribljih spermatozoide ukljucujuci i efekte temperature na metabolizam ATP-a

Ovarian fluid impacts flagellar beating and biomechanical metrics of sperm between alternative reproductive tactics

Alternative reproductive tactics (ARTs) are prevalent in nature, where smaller parasitic males typically have better sperm quality than larger territorial guard males. At present, it is unclear what is causing this phenomenon. Our objective was to gain insights into sperm form and function by examining flagellar beating patterns (beat frequency, wave amplitude, bend length, bend angle, wave velocity) and biomechanical sperm metrics (velocity, hydrodynamic power output, propulsive efficiency) of wild spawning Chinook salmon ARTs. Ovarian fluid and milt were collected to form a series of eight experimental blocks, each composed of ovarian fluid from a unique female and sperm from a unique pair of parasitic jack and guard hooknose males. Sperm from each ART were activated in river water and ovarian fluid. Flagellar parameters were evaluated from recordings using high-speed video microscopy and biomechanical metrics were quantified. We show that ART has an impact on flagellar beating, where jacks had a higher bend length and bend angle than hooknoses. Activation media also impacted the pattern of flagellar parameters, such that beat frequency, wave velocity and bend angle declined, while wave amplitude of flagella increased when ovarian fluid was incorporated into activation media. Furthermore, we found that sperm from jacks swam faster than those from hooknoses and required less hydrodynamic power output to propel themselves in river water and ovarian fluid. Jack sperm were also more efficient at swimming than hooknose sperm, and propulsive efficiency increased when cells were activated in ovarian fluid. The results demonstrate that sperm biomechanics may be driving divergence in competitive reproductive success between ARTs

Does the rainbow trout ovarian fluid promote the spermatozoon on its way to the egg?

The fertilization of freshwater fish occurs in an environment that may negatively affect the gametes; therefore, the specific mechanisms triggering the encounters of gametes would be highly expedient. The egg and ovarian fluid are likely the major sources of these triggers, which we confirmed here for rainbow trout (Oncorhynchus mykiss). The ovarian fluid affected significantly spermatozoa performance: it supported high velocity for a longer period and changed the motility pattern from tumbling in water to straightforward moving in the ovarian fluid. Rainbow trout ovarian fluid induced a trapping chemotaxis-like effect on activated male gametes, and this effect depended on the properties of the activating medium. The interaction of the spermatozoa with the attracting agents was accompanied by the “turn-and-run” behavior involving asymmetric flagellar beating and Ca2+ concentration bursts in the bent flagellum segment, which are characteristic of the chemotactic response. Ovarian fluid created the optimal environment for rainbow trout spermatozoa performance, and the individual peculiarities of the egg (ovarian fluid)–sperm interaction reflect the specific features of the spawning process in this species

Biological characteristics of sperm in European flat oyster (Ostrea edulis)

In brooding mollusc species that incubate larvae before their release in seawater, the biology of gametes remains poorly explored. The present study describes some biological characteristics of sperm of the European flat oyster, a native species that has been over-exploited in the past and is nowadays classified as an endangered species in Europe. Flat oysters were collected by divers in the Rade de Brest (Finistère, France), during its natural reproduction period. Gonadal pH is acidic (6.31 ± 0.10). Spermatozoa are clustered in spermatozeugmata, an acellular structure in which the sperm heads are embedded. After their transfer in seawater, spermatozeugmata have a mean diameter of 64 ± 3 μm and they release free spermatozoa for a mean duration of 21 ± 3 min. Immediately after their release, the mean percentage of motile spermatozoa was 48.5 ± 12.6%. At 10 min after dilution in seawater, movement of spermatozoa was no more observed. Biological characteristics of European flat oyster sperm are compared to those observed in the Pacific oyster, regarding the unique reproductive behaviour of the former species and the role of spermatozoa transfer played by spermatozeugmata. The present results aim to improve the knowledge of reproduction and natural recruitment processes, support conservation and restoration measures and favour the establishment of management protocols of gametes and larvae in this endangered species

Protein phosphorylation and ions effects on salmonid sperm motility activation

Sperm motility is considered as a key factor allowing determination of semen quality and predicts fertilizing capacity. In many fish species, the spermatozoa are immotile in the testes and seminal plasma, and motility is induced when they are released in the aqueous environment. Initiation and activation of sperm motility are prerequisite processes for the contact and fusion of male and female gametes at fertilization. Many proteins are involved in the activation of sperm motility in many species. Cell signalling for the initiation of sperm motility in the salmonid fish has drawn much attention during the last two decades. In some species, protein phosphorylation process was shown to be involved in flagellar motility regulation. Hyperpolarization of the sperm membrane induces synthesis of cAMP (cyclic AMP), which triggers further cell signalling processes, such as cAMP-dependent protein phosphorylation that finally initiates sperm motility in salmonid fish. Ions such as Na+, K+ and Ca2+ play also an important role in the activation of sperm motility in many species, more specifically in salmonids. Salmonid fish sperm motility can be suppressed by millimolar concentrations of extracellular K+, and dilution of K+ upon spawning is enough to trigger the cAMP-dependent signalling cascade leading to motility initiation. This review aims to update the present knowledge about the roles of ions and protein phosphorylation process in the sperm motility activation in salmonid

Sperm collection and storage for the sustainable management of amphibian biodiversity

Current rates of biodiversity loss pose an unprecedented challenge to the conservation community, particularly with amphibians and freshwater fish as the most threatened vertebrates. An increasing number of environmental challenges, including habitat loss, pathogens, and global warming, demand a global response toward the sustainable management of ecosystems and their biodiversity. Conservation Breeding Programs (CBPs) are needed for the sustainable management of amphibian species threatened with extinction. CBPs support species survival while increasing public awareness and political influence. Current CBPs only cater for 10% of the almost 500 amphibian species in need. However, the use of sperm storage to increase efficiency and reliability, along with an increased number of CBPs, offer the potential to significantly reduce species loss. The establishment and refinement of techniques over the last two decades, for the collection and storage of amphibian spermatozoa, gives confidence for their use in CBPs and other biotechnical applications. Cryopreserved spermatozoa has produced breeding pairs of frogs and salamanders and the stage is set for Lifecycle Proof of Concept Programs that use cryopreserved sperm in CBPs along with repopulation, supplementation, and translocation programs. The application of cryopreserved sperm in CBPs, is complimentary to but separate from archival gene banking and general cell and tissue storage. However, where appropriate amphibian sperm banking should be integrated into other global biobanking projects, especially those for fish, and those that include the use of cryopreserved material for genomics and other research. Research over a broader range of amphibian species, and more uniformity in experimental methodology, is needed to inform both theory and application. Genomics is revolutionising our understanding of biological processes and increasingly guiding species conservation through the identification of evolutionary significant units as the conservation focus, and through revealing the intimate relationship between evolutionary history and sperm physiology that ultimately affects the amenability of sperm to refrigerated or frozen storage. In the present review we provide a nascent phylogenetic framework for integration with other research lines to further the potential of amphibian sperm banking

Basal Body Positioning Is Controlled by Flagellum Formation in Trypanosoma brucei

To perform their multiple functions, cilia and flagella are precisely positioned at the cell surface by mechanisms that remain poorly understood. The protist Trypanosoma brucei possesses a single flagellum that adheres to the cell body where a specific cytoskeletal structure is localised, the flagellum attachment zone (FAZ). Trypanosomes build a new flagellum whose distal tip is connected to the side of the old flagellum by a discrete structure, the flagella connector. During this process, the basal body of the new flagellum migrates towards the posterior end of the cell. We show that separate inhibition of flagellum assembly, base-to-tip motility or flagella connection leads to reduced basal body migration, demonstrating that the flagellum contributes to its own positioning. We propose a model where pressure applied by movements of the growing new flagellum on the flagella connector leads to a reacting force that in turn contributes to migration of the basal body at the proximal end of the flagellum