In vivo volumetric depth-resolved imaging of cilia metachronal waves using dynamic optical coherence tomography

Advances in Imaging Techniques for Mammalian/Human Ciliated Cell's Cilia: Insights into Structure, Function, and Dynamics

Cilia are evolutionarily conserved, microtubule-based organelles characterized by their ultrastructures and diverse functional roles, including developmental signaling, mechanosensation, and fluid propulsion. They are widely distributed across cell surfaces and play crucial roles in cell cycle regulation and tissue homeostasis. Despite advances in studying their molecular regulation and functions, demonstrating the precise ultrastructure of cilia remains a challenge. Recent novel microscopy techniques, such as super-resolution microscopy and volume electron microscopy, are revolutionizing our understanding of their architecture and mechanochemical signaling. By integrating findings from different methodologies, this review highlights how these advances bridge basic research and clinical applications and provide a comprehensive understanding of the structural organization, functional mechanisms, and dynamic changes of cilia.

Straining Flow Effects on Sperm Flagellar Energetics in Microfluidic Cross-Slot Traps

Sperm need to effectively navigate the intricate pathways of the female reproductive tract, which are filled with various complex fluid flows. Despite numerous population-based studies, the effects of flow on the flagellar beating pattern of individual sperm remain poorly understood. In this study, a microfluidic cross-slot trap is employed to immobilize individual motile sperm for an extended period without physical tethering, thereby reducing potential cell damage and movement restriction compared to the conventional head-tethering method. The impact of pure straining flow on trapped single sperm is investigated. The experimental results demonstrate that at strain rates of 11.33 s-1 and higher, the periodic and repetitive beating pattern of the sperm flagellum changes to irregular movement. Furthermore, an increase in strain rate from 1.89 to 11.33 s-1 leads to a 35.4% reduction in beating amplitude and a 41.2% decrease in hydrodynamic power dissipation. These findings underscore the capability of the microfluidic cross-slot platform to trap sperm with high stability, contributing to a better understanding of sperm behavior in response to fluid flows.

Region-specific roles of oviductal motile cilia in oocyte/embryo transport and fertility†

The physiological and clinical importance of motile cilia in reproduction is well recognized; however, the specific role they play in transport through the oviduct and how ciliopathies lead to subfertility and infertility are still unclear. The contribution of cilia beating, fluid flow, and smooth muscle contraction to overall progressive transport within the oviduct remains under debate. Therefore, we investigated the role of cilia in the oviduct transport of preimplantation eggs/embryos using a combination of genetic and advanced imaging approaches. We show that the region of the oviduct where cumulus-oocyte complex circling occurs, around the time of fertilization, is correlated with asymmetrical mucosal fold arrangement and non-radially distributed ciliated epithelium. Our results suggest that motile cilia, as well as mucosal fold asymmetry, may contribute to the local flow fields that help steer luminal contents away from the epithelial walls. We also present, in vivo, volumetric evidence of delayed egg transport in a genetic mouse model with disrupted motile cilia function in the female reproductive system. Females with Dnah5 deleted in the oviduct epithelium are subfertile and demonstrate disrupted motile cilia activity within the oviduct mucosa. Fifty percent of Dnah5 mutant females have delayed egg transport where cumulus-oocyte complexes did not progress to the ampulla at the expected time point and remained within the ovarian bursa. The integration of advanced imaging with genetic dysfunction of motile cilia provides valuable insights into oviductal transport. Potentially, these data could be valuable for better understanding and management of tubal pathologies and human infertility.

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.