RIMS Workshop
Biofluid Mechanics of Reproduction
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Overview:
Overview:
Biological fluids often contain complex features such as viscoelasticity and fluid-structure interactions, and the importance has been recognized in the studies of the reproductive system, including sperm and ovum transportation. The purpose of this workshop is to share recent advances in biofluids problems in reproduction and to explore new researches in various "dynamic" phenomena in the biology of fertilization and development. The workshop is held as a part of the RIMS Project 'Biofluids 2021'.
Date & Venue:
Date & Venue:
Date: Thursday, 29th, July - Friday, 30th, July 2021
Venue: Hybrid (zoom + RIMS, Kyoto University) Online on Zoom
The workshop will be held online due to the situation of COVID-19.
The workshop ended with great success! Thank you for your participations.
The recoded talks are available for registered participants until 13th August.
Plenary speakers
Plenary speakers
The flagellum is an actuated slender appendage whose motion is used for swimming by diverse cells, including spermatozoa. We will examine numerous aspects of spermatozoan swimming, ranging from its basic mechanics, to how videomicroscopy may be used to informing spermatozoan mechanics and dynamics as well as the response of sperm to its microenvironment. We will proceed to examine how our understanding of the individual spermatozoan swimmer may be extended to the dynamics of a small number of swimmers and subsequently a large population, before finishing with a discussion of advances in the development of refined modelling frameworks for spermatozoan mechanics.
Masaru Okabe (Osaka U.) [Video]
"Progress in the study of reproduction during the last 70 years...and unresolved issues"
In vitro fertilization had been unsuccessful for many years in mammals. In 1951 (70 years ago), by injecting rabbit spermatozoa into the oviduct before and after the ovulation, Dr. Chang and Dr. Austin independently discovered that the spermatozoa must spend a certain period of time in the female reproductive tract to acquire their fertilizing ability and this phenomenon was named sperm “capacitation”. Since these discoveries, researchers have been working on in vitro fertilization in mammals, enabling it in many species including humans. Research on in vitro fertilization continues to progress, with results showing, for example, that a fertilized egg can be obtained by injecting sperm into an egg using a pipet. Meanwhile, genetically modified animals enabling identification of many fertilization-related genes together with so many genes “specifically expressed in testis” were apparently not essential for fertilization. It is astonishingly difficult to predict the function of genes without the aid of relevant gene KO animals [1]. The transgenic spermatozoa allowed us to observe spermatozoa in vivo. It was demonstrated that a large number of spermatozoa in the female reproductive tract remain acrosome intact and the sperm number decreases during ascension towards the oviduct; in the oviduct, fertilization occurs in about a 1:1 sperm-egg ratio in mice.
Would “capacitation” explain why it requires so many vigorously motile spermatozoa to fertilize a single egg?
Reference
[1] M. Okabe, FEBS Lett 2018 Vol. 592, 2673
Invited speakers
Invited speakers
Yamada Gen (Wakayama Medical U.) [Video]
"Mouse reproductive organ, genitalia as a unique model for male/female differentiation and functions"
We have been analyzing on unique reproductive tissue, EXT genitalia (external genitalia). External genitalia show typical mode of dimorphic development (male/female types). In adult, it shows specific functions for erection, sperm transfer, ejaculation for male. In this talk, I will first talk about embryonic process of external genitalia developmental analyses particularly focusing on mesenchyme cell behaviors. In the latter half of talk, I will talk about our recent analysis (together with Dr.Hirashima) about erectile tissue (corporal cavernosum). I think these topics have significant scientific connections with “ model biology field” and hope we will have some collaboration together.
Chii Jou Chan (National University of Singapore) [Video]
"Tissue hydraulics in early mammalian development"
Many developmental processes involve the emergence of intercellular fluid and luminogenesis. This often results in a build up of hydrostatic pressure and signalling molecules in the lumen. However, the potential roles of lumina in cellular functions and tissue morphogenesis have yet to be fully explored. Using mouse blastocyst as a model, we show that hydraulic force during lumen expansion leads to robust control of blastocyst size and cell fate specification [1]. We further showed that lineage segregation of the inner cell mass (ICM) can be guided by biochemical signalling cues from within the lumen [2]. Interestingly, during mammalian folliculogenesis, a similar process occurs where a fluid-filled cavity emerges in the antral follicle. We are currently studying the dynamics and mechanisms of antral follicle development, with the goal of understanding how lumen expansion impacts the oocyte quality and the eventual ovulation. We propose that the interplay between lumen hydraulics, signalling and tissue mechanics provides a unified framework in understanding reproductive biology [3], with important implications in ovarian ageing and infertility treatment.
References
[1] Chan CJ, Costanzo M, Ruiz-Herrero T, Mönke G, Petrie R, Bergert M, Diz-Munoz A, Mahadevan L, Hiiragi T. Hydraulic control of mammalian embryo size and cell fate. Nature (2019) 571:112-116.
[2] Ryan AQ, Chan CJ, Graner F, Hiiragi T. Lumen expansion facilitates epiblast-primitive endoderm fate specification during mouse blastocyst formation. Developmental Cell (2019) 51, 1-14.
[3] Chan CJ, Hiiragi T. Integration of luminal pressure and signalling in tissue self-organisation. Development (2020) 147:dev181297
Toru Hyakutake (Yokohama National U.) [Video]
"Hydrodynamic study of bovine sperm motility and application to in vitro fertilization"
The navigation mechanism of mammalian sperm in the female reproductive tract is unclear due to its complex process. To elucidate the process whereby sperm arrive at an egg in the female reproductive organs, it is essential to investigate how rheological properties of the fluid around mammalian spermatozoa affect their motility. Mammalian spermatozoa in organisms with internal fertilization are required to swim in the cervical and oviductal mucus, whose rheological properties differ substantially from those of water. In this study, we experimentally observed sperm motion in fluids with various fluid rheological properties and investigated the influence of varying the viscosity and whether the fluid was Newtonian or non-Newtonian on the sperm motility. In a Newtonian fluid environment, as the viscosity increased, the motility of the sperm decreased. However, in a non-Newtonian fluid, the straight-line velocity and beat frequency were significantly higher than in a Newtonian fluid with comparable viscosity. As a result, the linearity of the sperm movement increased. Furthermore, we focused on the motion characteristics of hyperactivated bovine sperm and investigated the effect of the surrounding fluid on motility. We successfully induced hyperactivation of bovine sperm in high-viscosity non-Newtonian fluid. Hyperactivation resulted in an increase in curvilinear velocity and a decrease in straight-line velocity. In the high-viscosity non-Newtonian fluid, the hyperactivated sperm moved in a zig-zag pattern with regularity, different from the movement observed in a diluted solution. These results will provide useful information to understand the mechanism of sperm navigation for the in vitro fertilization process.
Kogiku Shiba (U. Tsukuba) [Video]
"The role of Ca2+ in the regulation of flagellar movement during sperm chemotaxis"
For the success of fertilization, sperm chemotaxis is known to be essential in many organisms. To direct sperm toward the eggs, a chemoattractant is released from the egg and modulates sperm flagellar waveforms. Regulation of asymmetry in sperm flagellar waveforms is very important to change sperm swimming trajectory. Ca2+ is known to play a key role in the regulation of asymmetry in flagellar waveforms. However, molecular mechanism how the formation and propagation of asymmetric waves are regulated by Ca2+ is still unclear.
By real-time intraflagellar Ca2+ imaging and detailed analysis of flagellar bending, we revealed a quick response of flagellar waveform with a transient increase of intracellular Ca2+ concentration during the chemotaxis in the ascidian Ciona intestinalis (Shiba et al., 2008). When sperm swim away from the source of chemoattractant, rapid Ca2+ influx causes asymmetric flagellar waveform, resulting in the turn movement. A calcium sensor protein, calaxin, which is associated with the outer arm dynein in the axoneme, plays a key role in the sperm waveform regulation in a Ca2+-dependent manner. Inhibition of calaxin causes the suppression of continuous asymmetric flagellar waveform required for chemotactic turn (Mizuno et al., 2012). These results suggest that calaxin plays a role in sustaining the asymmetrical waveform.
In this symposium, I introduce our analytical systems to visualize flagellar responses, including those for a real-time intraflagellar Ca2+ imaging and for detailed analysis of flagellar waveforms, and overview our recent results regarding the regulation of flagellar motility during sperm chemotaxis.
Swimming of spermatozoa is important for the fertilization process, and has been intensively studied in terms of fluid mechanics. However, there are still many unanswered questions about the complex flagellar motions that drive sperm swimming, in particular the interaction of the many flagella with the fluid motion. To solve this problem, it is necessary to construct a mechanical model to represent the force balance among the fluid drag force, the flagellar elastic force and the internal driving force. In this study, we develop a fluid-structure interaction model of swimming sperm with a finite element and boundary element coupling method.
First, the fluid drag and elastic forces were calculated from the experimentally observed flagellar waveforms, and the distribution of unknown internal driving force was obtained from the equilibrium equations. The driving force was strongly correlated with the local flagellar velocity, and was proportional to it. The driving force decreased where high local curvature of the flagellum, and this result is consistent with the previously proposed geometric clutch hypothesis. We then employed a curvature-related wave propagation model as a function of the driving force to analyze the fluid-solid interaction between two sperms. The two flagella were observed to be synchronized by the interaction of fluid motion and flagellar deformation. The elasto-hydrodynamic synchronization of flagella resulted in an increase in the swimming speeds, indicating that elasto-hydrodynamic synchronization is beneficial for cells in terms of swimming speed.
The oviduct, a duct connecting the periovarian space with the uterus, is indispensable for the transport of sperm and fertilized eggs/embryos to accomplish fertilization and implantation in mammals. To accomplish fertilization, ejaculated sperm migrate from the uterus to oviduct and fertilize oocytes in the oviductal ampulla. Although the migration of sperm from the oviductal isthmus to the ampulla is believed to be regulated by some taxis, including chemotaxis, rheotaxis, and thermotaxis, mechanisms of the sperm migration in the oviduct have not been fully understood. The oviduct exhibits smooth muscle (myosalpinx) contractions and ciliary beating, which coordinate the regulation of oviductal fluid flows. In this study, we focused on the role of myosalpinx contractions in the sperm migration. Administration of prifinium bromide to mice effectively suppressed myosalpinx contractions, resulting in a decreased in fertilization rate and an abrogation of high-speed back-and-forth/shuttling flows of oviductal fluids around the isthmus. In the isthmus, sperm formed a tight assemblage that was synchronized with the shuttling flows. The sperm assemblage was gradually loosened and then completely abolished near the ampulla. These results suggest that myosalpinx contractions play important roles in the formation of sperm assemblage in the isthmus, and in the transport of the assemblage to the middle region of the oviduct. It is also suggested that the motility of sperm is essential for the migration of sperm from the middle oviductal region to the ampulla. On the basis of the data obtained, the function of oviduct in mammalian fertilization are discussed.
Spermatogenic stem cells (SSCs) support the production of numerous sperm over long term. Classically, it has been thought to be true that individual stem cells repeat invariantly an asymmetric cell division giving rise to one self-renewing and one differentiating daughter cells at a definitive (closed) niche region. However, series of experiments including intravital live-imaging and fate tracing of pulse-labeled SSCs, combined with biophysical modeling, have revealed that mouse SSCs actively migrate over an open (facultative) niche environment over the basement membrane of the testicular seminiferous tubules, and select their fate behavior in a stochastic, i.e., probabilistic, manner, leading to a dynamics of neutral competition between SSCs. It is also suggested that such a dynamics is underpinned by an effective competition for limited amount of self-renewing factors (e.g., FGFs) secreted from the cells comprising the niche environment. In this workshop, based on the aforementioned observations, the link between the random behavior of individual SSCs and the robust population-level homeostatic behavior, which supports the persistent spermatogenesis, will be discussed.
References:
Nakamura et al. (2021) Cell Stem Cell, published online.
Kitadate et al., (2019) Cell Stem Cell 24, 79-92.
Hara et al., (2014) Cell Stem Cell 14, 658-672.
Nakagawa et al., (2010) Science 328, 62-67.
Registrations:
Registrations:
Application Deadline: please use the online application form below
There are opportunities of travel supports for onsite student/postdoc participants.
Friday, June11, 2021
Notification of Acceptance:
Monday, June 21, 2021
Registration Deadline: please use the online form for participation-only registration
Monday, July26, 2021-> Friday, July 30th
Applications:
Applications:
How to apply? Just two steps!
1. Prepare the information below.
1. Prepare the information below.
Your name / affiliation / position
Preferred presentation style (
oral/ participation only )Title and abstract (250 words or less)*oral presenters will be selected based on this abstract.Possibility of recording your presentation ( for online participants from countries with time difference )Your participation dates /
Preferred participation style (onsite or online)/Need for travel support/Residence and residential status
Organizers:
Organizers:
Lisa Fauci (Tulane U., USA)
Tsuyoshi Hirashima (Kyoto U.)
Kenta Ishimoto (Kyoto U.)
Contact:
Contact:
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