In vivo three-dimensional tracking of sperm behaviors in the mouse oviduct

Structural analysis of the female reptile reproductive system by micro-computed tomography and optical coherence tomography†

Volumetric data provide unprecedented structural insight to the reproductive tract and add vital anatomical context to the relationships between organs. The morphology of the female reproductive tract in non-avian reptiles varies between species, corresponding to a broad range of reproductive modes and providing valuable insight to comparative investigations of reproductive anatomy. However, reproductive studies in reptilian models, such as the brown anole studied here, have historically relied on histological methods to understand the anatomy. While these methods are highly effective for characterizing the cell types present in each organ, histological methods lose the 3D relationships between images and leave the architecture of the organ system poorly understood. We present the first comprehensive volumetric analyses of the female brown anole reproductive tract using two non-invasive, non-destructive imaging modalities: micro-computed tomography (microCT) and optical coherence tomography (OCT). Both are specialized imaging technologies that facilitate high-throughput imaging and preserve three-dimensional information. This study represents the first time that microCT has been used to study all reproductive organs in this species and the very first time that OCT has been applied to this species. We show how the non-destructive volumetric imaging provided by each modality reveals anatomical context including orientation and relationships between reproductive organs of the anole lizard. In addition to broad patterns of morphology, both imaging modalities provide the high resolution necessary to capture details and key anatomical features of each organ. We demonstrate that classic histological features can be appreciated within whole-organ architecture in volumetric imaging using microCT and OCT, providing the complementary information necessary to understand the relationships between tissues and organs in the reproductive system. This side-by-side imaging analysis using microCT and OCT allows us to evaluate the specific advantages and limitations of these two methods for the female reptile reproductive system.

Three-dimensional particle streak velocimetry based on optical coherence tomography for assessing preimplantation embryo movement in mouse oviduct in vivo

The mammalian oviduct (or fallopian tube) is a tubular organ hosting reproductive events leading to pregnancy. Dynamic 3D imaging of the mouse oviduct with optical coherence tomography (OCT) has recently emerged as a promising approach to study the hidden processes vital to elucidate the role of oviduct in mammalian reproduction and reproductive disorders. In particular, with an intravital window, in vivo OCT imaging is a powerful solution to studying how the oviduct transports preimplantation embryos towards the uterus for pregnancy, a long-standing question that is critical for uncovering the functional cause of tubal ectopic pregnancy. However, simultaneously tracking embryo movement and acquiring large-field-of-view images of oviduct activity in 3D has been challenging due to the generally limited volumetric imaging rate of OCT. A lack of OCT-based 3D velocimetry method for large, sparse particles acts as a technical hurdle for analyzing the mechanistic process of the embryo transport. Here, we report a new particle streak velocimetry method to address this hurdle. The method relies on the 3D streak of a moving particle formed during the acquisition of a single OCT volume, where double B-scans are acquired at each B-scan location to resolve ambiguity in assessing the movement of particle. We validated this method with the gold-standard, direct volumetric particle tracking in a flow phantom, and we demonstrated its in vivo applications for simultaneous velocimetry of embryos and imaging of oviduct. This work sets the stage for quantitative understanding of the oviduct transport function in vivo, and the method fills in a gap in OCT-based velocimetry, providing the potential to enable new applications in 3D flow imaging.

Sperm in the Mammalian Female Reproductive Tract: Surfing Through the Tract to Try to Beat the Odds

Mammalian sperm are deposited in the vagina or the cervix/uterus at coitus or at artificial insemination, and the fertilizing sperm move through the female reproductive tract to the ampulla of the oviduct, the site of fertilization. But the destination of most sperm is not the oviduct. Most sperm are carried by retrograde fluid flow to the vagina, are phagocytosed, and/or do not pass barriers on the pathway to the oviduct. The sperm that reach the site of fertilization are the exceptions and winners of one of the most stringent selection processes in nature. This review discusses the challenges sperm encounter and how the few sperm that reach the site of fertilization overcome them. The sperm that reach the goal must navigate viscoelastic fluid, swim vigorously and cooperatively along the walls of the female tract, avoid the innate immune system, and respond to potential cues to direct their movement.

TTC6-Mediated Stabilization of the Flagellum Annulus Ensures the Rapid and Directed Motion of Sperm

Sperm motility and structural integrity are essential for successful fertilization in vivo, and any hindrance of the correct assembly of the axoneme and peri-axonemal structures in the sperm flagellum can lead to fertility problems. While there has been considerable advancement in studying diseases related to the flagellum, the underlying mechanisms that control sperm movement are not yet fully understood. In this study, we reveal that the tetratricopeptide repeat protein 6 (Ttc6) gene, expressed mainly in the testes, plays a crucial role in maintaining male fertility in mice. We further demonstrate that the knockout of Ttc6 in mice results in decreased sperm motility and induces an abnormal circular swimming pattern, consequently leading to male subfertility. Morphological analysis showed an atypical hairpin-like appearance of the spermatozoa, and ultrastructural studies showed unsheathed flagella at the juncture between the midpiece and principal piece. Collectively, these findings suggest that TTC6 plays an essential role in maintaining the stability of the annulus region of the sperm flagellum, thus ensuring the swift and directed motion of sperm.

Optical coherence tomography for dynamic investigation of mammalian reproductive processes

The biological events associated with mammalian reproductive processes are highly dynamic and tightly regulated by molecular, genetic, and biomechanical factors. Implementation of live imaging in reproductive research is vital for the advancement of our understanding of normal reproductive physiology and for improving the management of reproductive disorders. Optical coherence tomography (OCT) is emerging as a promising tool for dynamic volumetric imaging of various reproductive processes in mice and other animal models. In this review, we summarize recent studies employing OCT-based approaches toward the investigation of reproductive processes in both, males and females. We describe how OCT can be applied to study structural features of the male reproductive system and sperm transport through the male reproductive tract. We review OCT applications for in vitro and dynamic in vivo imaging of the female reproductive system, staging and tracking of oocytes and embryos, and investigations of the oocyte/embryo transport through the oviduct. We describe how the functional OCT approach can be applied to the analysis of cilia dynamics within the male and female reproductive systems. We also discuss the areas of research, where OCT could find potential applications to progress our understanding of normal reproductive physiology and reproductive disorders.

β-Defensin 19/119 mediates sperm chemotaxis and is associated with idiopathic infertility

Sperm chemotaxis is required for guiding sperm toward the egg. However, the molecular identity of physiological chemoattractant and its involvement in infertility remain elusive. Here, we identify DEFB19/119 (mouse/human orthologs) as a physiological sperm chemoattractant. The epithelia of the female reproductive tract and the cumulus-oocyte complex secrete DEFB19/119 that elicits calcium mobilization via the CatSper channel and induces sperm chemotaxis in capacitated sperm. Manipulating the level of DEFB19 in mice determines the number of sperm arriving at the fertilization site. Importantly, we identify exon mutations in the DEFB119 gene in idiopathic infertile women with low level of DEFB119 in the follicular fluid. The level of DEFB119 correlates with the chemotactic potency of follicular fluid and predicts the infertile outcome with positive correlation. This study reveals the pivotal role of DEFB19/119 in sperm chemotaxis and demonstrates its potential application in the diagnosis of idiopathic infertility.

Squeezing the eggs to grow: The mechanobiology of mammalian folliculogenesis

The formation of functional eggs (oocyte) in ovarian follicles is arguably one of the most important events in early mammalian development since the oocytes provide the bulk genetic and cytoplasmic materials for successful reproduction. While past studies have identified many genes that are critical to normal ovarian development and function, recent studies have highlighted the role of mechanical force in shaping folliculogenesis. In this review, we discuss the underlying mechanobiological principles and the force-generating cellular structures and extracellular matrix that control the various stages of follicle development. We also highlight emerging techniques that allow for the quantification of mechanical interactions and follicular dynamics during development, and propose new directions for future studies in the field. We hope this review will provide a timely and useful framework for future understanding of mechano-signalling pathways in reproductive biology and diseases.

Tissue hydraulics in reproduction

The development of functional eggs and sperm are critical processes in mammalian development as they ensure successful reproduction and species propagation. While past studies have identified important genes that regulate these processes, the roles of luminal flow and fluid stress in reproductive biology remain less well understood. Here, we discuss recent evidence that support the diverse functions of luminal fluid in oogenesis, spermatogenesis and embryogenesis. We also review emerging techniques that allow for precise quantification and perturbation of tissue hydraulics in female and male reproductive systems, and propose new questions and approaches in this field. We hope this review will provide a useful resource to inspire future research in tissue hydraulics in reproductive biology and diseases.

Dynamic volumetric imaging and cilia beat mapping in the mouse male reproductive tract with optical coherence tomography

Spermatozoa transport within the male reproductive tract is a highly dynamic and biologically important reproductive event. However, due to the lack of live volumetric imaging technologies and quantitative measurements, there is little information on the dynamic aspect and regulation of this process. Here, we presented ex vivo dynamic volumetric imaging of the mouse testis, efferent duct, epididymis, and vas deferens at a micro-scale spatial resolution with optical coherence tomography (OCT). Micro computed tomography imaging is presented as a reference for the proposed OCT imaging. Application of functional OCT analysis allowed for 3D mapping of the cilia beat frequency in the efferent duct, which volumetrically visualized the spatial distribution of the ciliated cells and corresponding ciliary activities. Potentially these analyses could be expanded to in vivo settings through intravital approach. In summary, this study demonstrated that OCT has a great potential to investigate the microstructure and dynamics, such as cilia beating, muscle contractions, and sperm transport, within the male reproductive tract.

Sperm-oviduct interactions: Key factors for sperm survival and maintenance of sperm fertilizing capacity

Background

Although millions or even billions of sperm are deposited in the female genital tract, only very few sperm reach the oocyte, and only one single spermatozoon will successfully fertilize. During the journey of the sperm within the female genital tract, the interactions between spermatozoa and fallopian tube are critical for sperm selection, sperm survival, and maintenance of sperm fertilizing capacity.

Results

This review will provide a comprehensive overview of the latest findings regarding sperm transport and behavior of sperm within the oviduct, sperm selection in the oviduct, the formation of the sperm reservoir, and the release of sperm in the presence of the oocyte. It will primarily focus on recent novel insights on sperm‐oviduct interactions, which have been obtained by cutting‐edge technologies under in vivo or near in vivo conditions.

Conclusions

The comprehensive analysis of the findings to date will elucidate the complex molecular changes in the tubal epithelium, which are induced by the presence of the sperm and will highlight how the epithelial cells of this organ affect transport, behavior, and function of sperm. This knowledge is essential for scientists and clinicians involved in assisted reproductive technologies.

Lgr4 Regulates Oviductal Epithelial Secretion Through the WNT Signaling Pathway

The WNT signaling pathway plays a crucial role in oviduct/fallopian development. However, the specific physiological processes regulated by the WNT pathway in the fallopian/oviduct function remain obscure. Benefiting from the Lgr4 knockout mouse model, we report the regulation of oviduct epithelial secretion by LGR4. Specifically, the loss of Lgr4 altered the mouse oviduct size and weight, severely reduced the number of oviductal epithelial cells, and ultimately impaired the epithelial secretion. These alterations were mediated by a failure of CTNNB1 protein accumulation in the oviductal epithelial cytoplasm, by the modulation of WNT pathways, and subsequently by a profound change of the gene expression profile of epithelial cells. In addition, selective activation of the WNT pathway triggered the expression of steroidogenic genes, like Cyp11a1 and 3β-Hsd1, through the activation of the transcriptional factor NR5A2 in an oviduct primary cell culture system. As demonstrated, the LGR4 protein modulates a WNT-NR5A2 signaling cascade facilitating epithelial secretory cell maturation and steroidogenesis to safeguard oviduct development and function in mice.

Postcopulatory sexual selection is associated with sperm aggregate quality in Peromyscus mice

In some species, sperm form coordinated groups that are hypothesized to improve their swimming performance in competitive contexts or to navigate through the viscous fluids of the female reproductive tract. Here we investigate sperm aggregation across closely related species of Peromyscus mice that naturally vary by mating system to test the predictions that sperm aggregates 1) are faster than solitary sperm in species that females mate multiply to aid cells in sperm competition, and 2) outperform solitary sperm cells in viscous environments. We find significant variation in the size of sperm aggregates, which negatively associates with relative testis mass, a proxy for sperm competition risk, suggesting that postcopulatory sexual selection has a stabilizing effect on sperm group size. Moreover, our results show that sperm aggregates are faster than solitary sperm in some, but not all, species, and this can vary by fluid viscosity. Of the two species that produce the largest and most frequent groups, we find that sperm aggregates from the promiscuous P. maniculatus are faster than solitary sperm in every experimentally viscous environment but aggregation provides no such kinematic advantage under these same conditions for the monogamous P. polionotus. The reduced performance of P. polionotus aggregates is associated with less efficient aggregate geometry and the inclusion of immotile or morphological abnormal sperm. Our cross-species comparison yields insight into the evolution of sperm social behaviors, provides evidence of extensive variation in the Peromyscus lineage, and reveals that differences in sperm aggregate quality associate with postcopulatory sexual selection.

Rolling controls sperm navigation in response to the dynamic rheological properties of the environment

Mammalian sperm rolling around their longitudinal axes is a long-observed component of motility, but its function in the fertilization process, and more specifically in sperm migration within the female reproductive tract, remains elusive. While investigating bovine sperm motion under simple shear flow and in a quiescent microfluidic reservoir and developing theoretical and computational models, we found that rolling regulates sperm navigation in response to the rheological properties of the sperm environment. In other words, rolling enables a sperm to swim progressively even if the flagellum beats asymmetrically. Therefore, a rolling sperm swims stably along the nearby walls (wall-dependent navigation) and efficiently upstream under an external fluid flow (rheotaxis). By contrast, an increase in ambient viscosity and viscoelasticity suppresses rolling, consequently, non-rolling sperm are less susceptible to nearby walls and external fluid flow and swim in two-dimensional diffusive circular paths (surface exploration). This surface exploration mode of swimming is caused by the intrinsic asymmetry in flagellar beating such that the curvature of a sperm's circular path is proportional to the level of asymmetry. We found that the suppression of rolling is reversible and occurs in sperm with lower asymmetry in their beating pattern at higher ambient viscosity and viscoelasticity. Consequently, the rolling component of motility may function as a regulatory tool allowing sperm to navigate according to the rheological properties of the functional region within the female reproductive tract.

In vivo dynamic 3D imaging of oocytes and embryos in the mouse oviduct

Developmental biologists have always relied on imaging to shed light on dynamic cellular events. However, processes such as mammalian fertilization and embryogenesis are generally inaccessible for direct imaging. In consequence, how the oviduct (fallopian tube) facilitates the transport of gametes and preimplantation embryos continues to be unanswered. Here we present a combination of intravital window and optical coherence tomography for dynamic, volumetric, in vivo imaging of oocytes and embryos as they are transported through the mouse oviduct. We observed location-dependent circling, oscillating, and long-distance bi-directional movements of oocytes and embryos that suggest regulatory mechanisms driving transport and question established views in the field. This in vivo imaging approach can be combined with a variety of genetic and pharmacological manipulations for live functional analysis, bringing the potential to investigate reproductive physiology in its native state.

Wang and Larina present in vivo volumetric imaging of oocytes and embryos as they are transported through the mouse oviduct with optical coherence tomography and an intravital microscopy. The study reveals complex dynamics of oocytes and embryos that suggest a regulatory role of cilia and oviductal contractions in driving the transport.

Getting to and away from the egg, an interplay between several sperm transport mechanisms and a complex oviduct physiology

In mammals, the architecture and physiology of the oviduct are very complex, and one long-lasting intriguing question is how spermatozoa are transported from the sperm reservoir in the isthmus to the oocyte surface. In recent decades, several studies have improved knowledge of the factors affecting oviduct fluid movement and sperm transport. They report sperm-guiding mechanisms that move the spermatozoa towards (rheotaxis, thermotaxis, and chemotaxis) or away from the egg surface (chemorepulsion), but only a few provide evidence of their occurrence in vivo. This gives rise to several questions: how and when do the sperm transport mechanisms operate inside such an active oviduct? why are there so many sperm guidance processes? is one dominant over the others, or do they cooperate to optimise the success of fertilisation? Assuming that sperm guidance evolved alongside oviduct physiology, in this review we propose a theoretical model that integrates oviduct complexity in space and time with the sperm-orienting mechanisms. In addition, since all of the sperm-guidance processes recruit spermatozoa in a better physiological condition than those not selected, they could potentially be incorporated into assisted reproductive technology (ART) to improve fertility treatment and/or to develop innovative contraceptive methods. All these issues are discussed in this review.

Cfap97d1 is important for flagellar axoneme maintenance and male mouse fertility

The flagellum is essential for sperm motility and fertilization in vivo. The axoneme is the main component of the flagella, extending through its entire length. An axoneme is comprised of two central microtubules surrounded by nine doublets, the nexin-dynein regulatory complex, radial spokes, and dynein arms. Failure to properly assemble components of the axoneme in a sperm flagellum, leads to fertility alterations. To understand this process in detail, we have defined the function of an uncharacterized gene, Cfap97 domain containing 1 (Cfap97d1). This gene is evolutionarily conserved in mammals and multiple other species, including Chlamydomonas. We have used two independently generated Cfap97d1 knockout mouse models to study the gene function in vivo. Cfap97d1 is exclusively expressed in testes starting from post-natal day 20 and continuing throughout adulthood. Deletion of the Cfap97d1 gene in both mouse models leads to sperm motility defects (asthenozoospermia) and male subfertility. In vitro fertilization (IVF) of cumulus-intact oocytes with Cfap97d1 deficient sperm yielded few embryos whereas IVF with zona pellucida-free oocytes resulted in embryo numbers comparable to that of the control. Knockout spermatozoa showed abnormal motility characterized by frequent stalling in the anti-hook position. Uniquely, Cfap97d1 loss caused a phenotype associated with axonemal doublet heterogeneity linked with frequent loss of the fourth doublet in the sperm stored in the epididymis. This study demonstrates that Cfap97d1 is required for sperm flagellum ultra-structure maintenance, thereby playing a critical role in sperm function and male fertility in mice.

Collective dynamics of sperm cells

While only a single sperm may fertilize the egg, getting to the egg can be facilitated, and possibly enhanced, by sperm group dynamics. Examples range from the trains formed by wood mouse sperm to the bundles exhibited by echidna sperm. In addition, observations of wave-like patterns exhibited by ram semen are used to score prospective sample fertility for artificial insemination in agriculture. In this review, we discuss these experimental observations of collective dynamics, as well as describe recent mechanistic models that link the motion of individual sperm cells and their flagella to observed collective dynamics. Establishing this link in models involves negotiating the disparate time- and length scales involved, typically separated by a factor of 1000, to capture the dynamics at the greatest length scales affected by mechanisms at the shortest time scales. Finally, we provide some outlook on the subject, in particular, the open questions regarding how collective dynamics impacts fertility. This article is part of the theme issue 'Multi-scale analysis and modelling of collective migration in biological systems'.

Self-organization and multi-line transport of human spermatozoa in rectangular microchannels due to cell-cell interactions

The journey of sperm navigation towards ovum is one of the most important questions in mammalian fertilisation and reproduction. However, we know very little about spermatozoa propagation in a complex fluidic, chemical and topographic environment of a fertility tract. Using microfluidics techniques, we investigate the influence of cell-cell interactions on spermatozoa swimming behavior in constrained environment at different concentrations. Our study shows that at high enough cell concentration the interaction between boundary-following cells leads to formation of areas with preferential direction of cell swimming. In the microchannel of a rectangular cross-section, this leads to formation of a “four-lane” swimming pattern with the asymmetry of the cell distribution of up to 40%. We propose that this is caused by the combination of cell-cell collisions in the corners of the microchannel and the existence of morphologically different spermatozoa: slightly asymmetric cells with trajectories curved left and the symmetric ones, with trajectories curved right. Our findings suggest that cell-cell interactions in highly folded environment of mammalian reproductive tract are important for spermatozoa swimming behavior and play role in selection of highly motile cells.

Methodological considerations for examining the relationship between sperm morphology and motility

Sperm cells of all taxa share a common goal to reach and fertilize an ovum, yet sperm are one of the most diverse cell types in nature. While the structural diversity of these cells is well recognized, the functional significance of variation in sperm design remains elusive. An important function of spermatozoa is a need to migrate toward the ova, often over long distances in a foreign environment, which may include a complex and hostile female reproductive tract. Several comparative and experimental studies have attempted to address the link between sperm morphology and motility, yet the conclusions drawn from these studies are often inconsistent, even within the same taxa. Much of what we know about the functional significance of sperm design in internally fertilizing species has been gleaned from in vitro studies, for which experimental parameters often vary among studies. We propose that discordant results from these studies are in part due to a lack of consistency of methods, conditions that do not replicate those of the female reproductive tract, and the overuse of simple linear measures of sperm shape. Within this review, we provide a toolkit for imaging, quantifying, and analyzing sperm morphology and movement patterns for in vitro studies and discuss emerging approaches. Results from studies linking morphology to motility enhance our understanding of the evolution of adaptive sperm traits and the mechanisms that regulate fertility, thus offering new insights into methods used in assisted reproductive technologies in animal science, conservation and public health.

Perfect date-the review of current research into molecular bases of mammalian fertilization

Fertilization is a multistep process during which two terminally differentiated haploid cells, an egg and a sperm, combine to produce a totipotent diploid zygote. In the early 1950s, it became possible to fertilize mammalian eggs in vitro and study the sequence of cellular and molecular events leading to embryo development. Despite all the achievements of assisted reproduction in the last four decades, remarkably little is known about the molecular aspects of human conception. Current fertility research in animal models is casting more light on the complexity of the process all our lives start with. This review article provides an update on the investigation of mammalian fertilization and highlights the practical implications of scientific discoveries in the context of human reproduction and reproductive medicine.

A tale of two tracts: history, current advances, and future directions of research on sexual differentiation of reproductive tracts†

Alfred Jost's work in the 1940s laid the foundation of the current paradigm of sexual differentiation of reproductive tracts, which contends that testicular hormones drive the male patterning of reproductive tract system whereas the female phenotype arises by default. Once established, the sex-specific reproductive tracts undergo morphogenesis, giving rise to anatomically and functionally distinct tubular organs along the rostral-caudal axis. Impairment of sexual differentiation of reproductive tracts by genetic alteration and environmental exposure are the main causes of disorders of sex development, and infertility at adulthood. This review covers past and present work on sexual differentiation and morphogenesis of reproductive tracts, associated human disorders, and emerging technologies that have made impacts or could radically expand our knowledge in this field.

Chronic fetal hypoxia disrupts the peri-conceptual environment in next-generation adult female rats

KEY POINTS

Exposure to chronic hypoxia during gestation influences long-term health and development, including reproductive capacity, across generations. If the peri-conceptual environment in the developing oviduct is affected by gestational hypoxia, then this could have implications for later fertility and the health of future generations. In the present study, we show that the oviducts of female rats exposed to chronic hypoxia in utero have reduced telomere length, decreased mitochondrial DNA biogenesis and increased oxidative stress The results of the present study show that exposure to chronic gestational hypoxia leads to accelerated ageing of the oviduct in early adulthood and they help us understand how exposure to hypoxia during development could influence reproductive health across generations.

ABSTRACT

Exposure to chronic hypoxia during fetal development has important effects on immediate and long-term outcomes in offspring. Adverse impacts in adult offspring include impairment of cardiovascular function, metabolic derangement and accelerated ovarian ageing. However, it is not known whether other aspects of the female reproductive system may be similarly affected. In the present study, we examined the impact of chronic gestational hypoxia on the developing oviduct. Wistar rat dams were randomized to either normoxia (21%) or hypoxia (13%) from day 6 post-mating until delivery. Post-delivery female offspring were maintained in normoxia until 4 months of age. Oviductal gene expression was assayed at the RNA (quantitative RT-PCR) and protein (western blotting) levels. Oviductal telomere length was assayed using Southern blotting. Oviductal telomere length was reduced in the gestational hypoxia-exposed animals compared to normoxic controls (P < 0.01). This was associated with a specific post-transcriptional reduction in the KU70 subunit of DNA-pk in the gestational hypoxia-exposed group (P < 0.05). Gestational hypoxia-exposed oviducts also showed evidence of decreased mitochondrial DNA biogenesis, reduced mtDNA copy number (P < 0.05) and reduced gene expression of Tfam (P < 0.05) and Pgc1α (P < 0.05). In the hypoxia-exposed oviducts, there was upregulation of mitochondrial-specific anti-oxidant defence enzymes (MnSOD; P < 0.01). Exposure to chronic gestational hypoxia leads to accelerated ageing of the oviduct in adulthood. The oviduct plays a central role in early development as the site of gamete transport, syngamy, and early development; hence, accelerated ageing of the oviductal environment could have important implications for fertility and the health of future generations.

Behavior of ACRBP-deficient mouse sperm in the female reproductive tract

Gene-knockout mice lacking ACRBP, a proacrosin-binding protein localized in the acrosome of sperm, have been shown to exhibit male subfertility, owing to abnormal formation of the acrosome. In this study, to elucidate the mechanism contributing to the subfertility phenotype, we examined the behavior of ACRBP-deficient mouse sperm in the female reproductive tract. When sperm that had migrated into the uterus and oviduct after mating were counted, the number of ACRBP-deficient sperm was noticeably smaller in the oviduct of mice post mating. However, ACRBP-deficient sperm recovered from the oviduct possessed morphologically normal head shape and retained normal motility. Importantly, ACRBP-deficient sperm displayed a marked reduction in the ability to successfully gain access to unfertilized oocytes. These data suggest that male subfertility of ACRBP-deficient mice may be attributed to incompleteness of the acrosome reaction rather than impairment in sperm migration from the uterus to the oviduct.

Biophysics in oviduct: Planar cell polarity, cilia, epithelial fold and tube morphogenesis, egg dynamics

Organs and tissues in multi-cellular organisms exhibit various morphologies. Tubular organs have multi-scale morphological features which are closely related to their functions. Here we discuss morphogenesis and the mechanical functions of the vertebrate oviduct in the female reproductive tract, also known as the fallopian tube. The oviduct functions to convey eggs from the ovary to the uterus. In the luminal side of the oviduct, the epithelium forms multiple folds (or ridges) well-aligned along the longitudinal direction of the tube. In the epithelial cells, cilia are formed orienting toward the downstream of the oviduct. The cilia and the folds are supposed to be involved in egg transportation. Planar cell polarity (PCP) is developed in the epithelium, and the disruption of the Celsr1 gene, a PCP related-gene, causes randomization of both cilia and fold orientations, discontinuity of the tube, inefficient egg transportation, and infertility. In this review article, we briefly introduce various biophysical and biomechanical issues in the oviduct, including physical mechanisms of formation of PCP and organized cilia orientation, epithelial cell shape regulation, fold pattern formation generated by mechanical buckling, tubulogenesis, and egg transportation regulated by fluid flow. We also mention about possible roles of the oviducts in egg shape formation and embryogenesis, sinuous patterns of tubes, and fold and tube patterns observed in other tubular organs such as the gut, airways, etc.

New Insights into the Molecular Events of Mammalian Fertilization

Currently, infertility affects ∼16% of couples worldwide. The causes are reported to involve both male and female factors, including fertilization failure between mature spermatozoa and eggs. However, the molecular mechanisms involved in each step of mammalian fertilization are yet to be fully elucidated. Although some of these steps can be rescued with assisted reproductive technologies, it is important to clarify the molecular mechanisms involved for the treatment and diagnosis of infertile couples. This review illustrates recent findings in mammalian fertilization, discovered by combining gene modification techniques with other new approaches, and aims to show how these findings will guide future research in mammalian fertilization.