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.

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

Fertilization of freshwater fish occurs in an environment that may affect negatively the gametes, therefore the specific mechanisms triggering the encounters of gametes would be highly expedient. The egg and ovarian fluid (OF) are likely the major sources of these triggers in fish, that we confirmed here for rainbow trout Oncorhynchus mykiss. The ovarian fluid affected significantly the 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 OF induced a trapping chemotaxis-like effect on activated male gametes and this effect depended on the properties of the activating media. The interaction of the sper-matozoa with the attracting agents was accompanied by their 'turn-and-run' behavior involving asymmetric flagellar beating and Ca2+ concentration bursts in the bent flagella segment, characteristic for the chemotactic response. Collectively, the ovarian fluid creates the optimal environment for rainbow trout spermatozoa performance, being an effective promoter of fertilization. The individual peculiarities of the egg (ovarian fluid)-sperm interaction in rainbow trout reflect the specific features of the spawning process in this species.

Modelling and Simulation of the Drug Release from a Solid Dosage Form in the Human Ascending Colon: The Influence of Different Motility Patterns and Fluid Viscosities

For colonic drug delivery, the ascending part of the colon is the most favourable site as it offers the most suitable environmental conditions for drug dissolution. Commonly, the performance of a drug formulation is assessed using standardised dissolution apparatus, which does not replicate the hydrodynamics and shear stress evoked by wall motion in the colon. In this work, computer simulations are used to analyse and understand the influence of different biorelevant motility patterns on the disintegration/drug release of a solid dosage form (tablet) under different fluid conditions (viscosities) to mimic the ascending colonic environment. Furthermore, the ability of the motility pattern to distribute the drug in the ascending colon luminal environment is analysed to provide data for a spatiotemporal concentration profile. The motility patterns used are derived from in vivo data representing different motility patterns in the human ascending colon. The applied motility patterns show considerable differences in the drug release rate from the tablet, as well as in the ability to distribute the drug along the colon. The drug dissolution/disintegration process from a solid dosage form is primarily influenced by the hydrodynamic and shear stress it experiences, i.e., a combination of motility pattern and fluid viscosity. Reduced fluid motion leads to a more pronounced influence of diffusion in the tablet dissolution process. The motility pattern that provoked frequent single shear stress peaks seemed to be more effective in achieving a higher drug release rate. The ability to simulate drug release profiles under biorelevant colonic environmental conditions provides valuable feedback to better understand the drug formulation and how this can be optimised to ensure that the drug is present in the desired concentration within the ascending colon.

Cooperation of two opposite flagella allows high-speed swimming and active turning in zoospores

Phytophthora species cause diseases in a large variety of plants and represent a serious agricultural threat, leading, every year, to multibillion dollar losses. Infection occurs when these biflagellated zoospores move across the soil at their characteristic high speed and reach the roots of a host plant. Despite the relevance of zoospore spreading in the epidemics of plant diseases, it is not known how these zoospores swim and steer with two opposite beating flagella. Here, combining experiments and modeling, we show how these two flagella contribute to generate thrust when beating together, and identify the mastigonemes-attached anterior flagellum as the main source of thrust. Furthermore, we find that steering involves a complex active process, in which the posterior flagellum is stopped, while the anterior flagellum keeps on beating, as the zoospore reorients its body. Our study is a fundamental step towards a better understanding of the spreading of plant pathogens’ motile forms, and shows that the motility pattern of these biflagellated zoospores represents a distinct eukaryotic version of the celebrated “run-and-tumble” motility class exhibited by peritrichous bacteria.

Run-and-Halt Behavior of Motile Droplets in Response to Light

<p>We report the run-and-halt behavior of motile droplets immersed in an aqueous solution of amphiphilic molecular switch. These oil droplets move autonomously as the switch solubilizes the oil into the water. Droplet movement stops in response to UV light, and picks up again in response to visible light. This motile behavior is a consequence of the reversible <i>trans-</i>to-<i>cis</i> photo-conversion of the switch in water, because the <i>trans</i> photo-isomer stabilizes the oil droplets better than the <i>cis</i> photo-isomer, and therefore it also solubilizes the droplet more effectively. Notably, the droplets also evolve positive photokinesis under illumination with visible light, and, in patchy light environments, their complex motility pattern directs the droplets at the periphery of the illuminated areas. </p>

Run-and-Halt Behavior of Motile Droplets in Response to Light

<p>We report the run-and-halt behavior of motile droplets immersed in an aqueous solution of amphiphilic molecular switch. These oil droplets move autonomously as the switch solubilizes the oil into the water. Droplet movement stops in response to UV light, and picks up again in response to visible light. This motile behavior is a consequence of the reversible <i>trans-</i>to-<i>cis</i> photo-conversion of the switch in water, because the <i>trans</i> photo-isomer stabilizes the oil droplets better than the <i>cis</i> photo-isomer, and therefore it also solubilizes the droplet more effectively. Notably, the droplets also evolve positive photokinesis under illumination with visible light, and, in patchy light environments, their complex motility pattern directs the droplets at the periphery of the illuminated areas. </p>