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

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.

Optimizing optical coherence tomography to detect occult spermatozoa in rat testis after induced non-obstructive azoospermia

Significance

The ability to detect and localize sperm in the testes is crucial for the treatment of non-obstructive azoospermia (NOA), a condition where sperm retrieval is challenging due to the lack of visible sperm. Enhancing the accuracy and efficiency of sperm detection can significantly improve the outcomes of microdissection testicular sperm extraction (micro-TESE) procedures in NOA patients.

Aim

We aim to use optical coherence tomography (OCT) to detect the presence or absence of sperm in the imaged areas of the testes and to localize sperm-containing seminiferous tubules in a rat model of NOA.

Approach

Volumetric OCT scanning was performed on 180 distinct regions from the testes of two control and 15 busulfan-treated rats to mimic NOA. Following scanning, excised tubules were observed under a dissecting microscope with transillumination to confirm the presence of sperm. The OCT data were processed by first delineating the tubule lumen and then evaluating the calibrated intensity and attenuation coefficient within the lumen. These quantifications, along with outer tubule diameter, were evaluated to identify sperm by comparison with the results of the microscope examination.

Results

Our OCT results revealed a significant correlation between the presence of sperm and high attenuation coefficients in a rat model of NOA. The accuracy of sperm detection by OCT is 97.8% when compared with microscopic identification. In addition, OCT data were utilized for color-coded processing to automatically distinguish regions with a greater likelihood of the presence of sperm, which may assist surgeons in locating occult sperm in NOA patients.

Conclusions

By providing high-resolution, non-invasive, automatic capture, and color-coded images, OCT has the potential to significantly enhance the efficiency of identification of tubules with spermatozoa during micro-TESE.

In vivo dynamic volumetric imaging of mouse testis and epididymis with optical coherence tomography†

The implementation of live imaging in reproductive research is crucial for studying the physiological dynamics. Sperm transport is a highly dynamic process regulated by tubular contractions and luminal flows within the male reproductive tract. However, due to the lack of imaging techniques to capture these dynamics in vivo, there is little information on the physiological and biomechanical regulation of sperm transport through the male reproductive tract. Here, we present a functional in vivo imaging approach using optical coherence tomography, enabling live, label-free, depth-resolved, three-dimensional, high-resolution visualization of the mouse testis and epididymis. With this approach, we spatiotemporally captured tubular contractility in mouse testis and epididymis, as well as microstructures of these reproductive organs. Our findings demonstrated that the contraction frequency varies significantly depending on the epididymal regions, suggesting the spatial regulation of epididymal contractility. Furthermore, we implemented quantitative measurements of the contraction wave and luminal transport through the epididymal duct, revealing the physiological dynamics within the male reproductive tract. The results show that the contraction wave propagates along the epididymal duct and the wave propagation velocity was estimated in vivo. In conclusion, this is the first study to develop in vivo dynamic volumetric imaging of the male reproductive tract, which allows for quantitative analysis of the dynamics associated with sperm transport. This study sets a platform for various studies investigating normal and abnormal male reproductive physiology as well as the pharmacological and environmental effects on reproductive functions in mouse models, ultimately contributing to a comprehensive understanding of male reproductive disorders.

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.

Mouse embryo phenotyping with optical coherence tomography

With the explosion of gene editing tools in recent years, there has been a much greater demand for mouse embryo phenotyping, and traditional methods such as histology and histochemistry experienced a methodological renaissance as they became the principal tools for phenotyping. However, it is important to explore alternative phenotyping options to maximize time and resources and implement volumetric structural analysis for enhanced investigation of phenotypes. Cardiovascular phenotyping, in particular, is important to perform in vivo due to the dramatic structural and functional changes that occur in heart development over relatively short periods of time. Optical coherence tomography (OCT) is one of the most exciting advanced imaging techniques emerging within the field of developmental biology, and this review provides a summary of how it is currently being implemented in mouse embryo investigations and phenotyping. This review aims to provide an understanding of the approaches used in optical coherence tomography and how they can be applied in embryology and developmental biology, with the overall aim of bridging the gap between biology and technology.