Single-cell insights into epithelial morphogenesis in the neonatal mouse uterus

Effectors and predictors of conceptus survival in cattle: What is next?

In cattle, the physiological process of switching from cycling to pregnant is complex. Ultimately, that process relies on endometrial luminal epithelial cells and is based on the paracrine context of the uterine lumen. Cells either release luteolytic pulses of prostaglandin F2 alpha to keep the animal cycling or respond to cues released by the elongated conceptus that block prostaglandin F2 alpha pulses to maintain luteal function and pregnancy. That process, however, is highly regulated and subjected to error that occurs in every 30 to 40 % of attempted bovine pregnancies. This review addresses novel aspects of endometrial cell function, luteal function, intraluminal endometrial-trophoblast communication, heat stress, and artificial intelligence as effectors, predictors, and tools to be explored and employed to reduce pregnancy loss.

Single cell multiome analysis of the bovine placenta identifies gene regulatory networks in trophoblast differentiation†

A central determinant of successful reproduction is pregnancy establishment and maintenance that relies on proper development of the conceptus (embryo/fetus and associated extraembryonic membranes including the placenta). Pregnancy loss in cattle can be caused by inadequate development and differentiation of the placenta. However, the cellular and molecular mechanisms regulating bovine placenta development and, particularly, trophoblast differentiation are not well understood. Recent single-cell RNA-seq analyses revealed dynamic changes in cell populations and gene expression patterns during bovine placental development. Here, the chromatin accessibility landscape across diverse cell populations was determined in the developing (Day 40) and mature (Day 170) bovine placenta using the 10X Genomics multiome (snRNA-seq and snATAC-seq) platform. Analyses revealed distinct trophoblast, mesenchyme, endothelial, immune, and epithelial cell populations characterized by unique gene expression and chromatin accessibility signatures. ATAC-seq peaks defined open chromatin regions, facilitating the identification of transcription factor binding sites and candidate gene regulatory networks involved with trophoblast differentiation. Several transcription factors, known for their involvement in trophoblast differentiation in other mammalian species, were identified as candidate regulators of uninucleate to binucleate trophoblast differentiation. This study adds to our foundational understanding of gene regulation and expression in the placenta, offering insights into the mechanisms governing pregnancy loss in cattle.

A refined method for high-purity isolation of uterine glandular epithelial cells in mouse

The uterine endometrium consists of luminal epithelium, glandular epithelium and stromal cells, with uterine glands playing a pivotal role in pregnancy success among mammals. Uterine glands secrete essential factors that regulate embryo development and implantation; however, their cellular biology remains poorly understood. This study presents a refined method for isolating three distinct endometrial cell types with high purity, with a specific emphasis on glandular epithelial (GE) cells. The method combines mechanical dissociation, enzymatic digestion and immunomagnetic separation. The isolated GE cells were maintained in culture and exhibited proliferation in response to steroid hormones. Furthermore, oestrogen responsiveness was abrogated by Estrogen Receptor 1 (Esr1) knockdown mediated by siRNA. Here, we present an efficient and reproducible method for isolating uterine GE cells with high purity, enabling their in vitro maintenance, hormone responsiveness assessment and functional gene knockdown. These findings establish a robust platform for advancing our understanding of uterine gland biology, facilitating detailed investigations into molecular mechanisms underlying glandular function and their critical roles in establishing pregnancy success. Future research could explore the contribution of these isolated cells to endometrial receptivity and embryo implantation.

Retinoic acid antagonizes estrogen signaling to maintain adult uterine cell fate

Classical tissue recombination experiments demonstrate that cell-fate determination along the anterior-posterior axis of the Müllerian duct occurs prior to postnatal day 7 in mice. However, little is known about how these cell types are maintained in adults. In this study, we provide genetic evidence that a balance between antagonistic retinoic acid (RA) and estrogen signaling activity is required to maintain simple columnar cell fate in adult uterine epithelium. Transdifferentiation of simple columnar uterine epithelium into stratified cervicovaginal-like epithelium was observed in three related mouse genetic models, in which RA signaling was perturbed in the postnatal uterus. Single-cell RNA sequencing analysis identified the transformed epithelial cell populations and revealed extensive immune cell infiltration resulting from loss of RA signaling. Surprisingly, disruption of RA signaling led to dysregulated expression of a substantial number of estrogen target genes, suggesting that these two pathways may functionally oppose each other in determining and maintaining uterine epithelial cell fate. Consistent with this model, neonatal exposure to the strong synthetic estrogen, diethylstilbestrol, downregulated expression of a group of RA target genes and led to epithelial stratification and immune cell infiltration in wild-type uterus. Treating RA receptor triple conditional knockout pups with fulvestrant, an estrogen antagonist, reestablished the balance between the two signaling pathways, and effectively prevented the transformation of mutant simple columnar epithelia to metaplastic stratified epithelia. These findings implicate an essential role for RA signaling in maintaining uterine cytodifferentiation by antagonizing estrogen signaling in the postnatal uterus.

Uterine organoids reveal insights into epithelial specification and plasticity in development and disease

Understanding how epithelial cells in the female reproductive tract (FRT) differentiate is crucial for reproductive health, yet the underlying mechanisms remain poorly defined. At birth, FRT epithelium is highly malleable, allowing differentiation into various epithelial types, but the regulatory pathways guiding these early cell fate decisions are unclear. Here, we use neonatal mouse endometrial organoids and assembloid coculture models to investigate how innate cellular plasticity and external mesenchymal signals influence epithelial differentiation. Our findings demonstrate that uterine epithelium undergoes marked age-dependent changes, transitioning from a highly plastic state capable of forming both monolayered and multilayered structures to a more restricted fate as development progresses. Interestingly, parallels emerge between the developmental plasticity of neonatal uterine epithelium and pathological conditions such as endometrial cancer, where similar regulatory mechanisms may reactivate, driving abnormal epithelial differentiation and tumorigenesis. These results not only deepen our understanding of early uterine development but also offer a valuable model for studying the progression of reproductive diseases and cancers.

Hydrogel Strategies for Female Reproduction Dysfunction

Infertility is an important issue for human reproductive health, with over half of all cases of infertility associated with female factors. Dysfunction of the complex female reproductive system may cause infertility. In clinical practice, female infertility is often treated with oral medications and/or surgical procedures, and ultimately with assisted reproductive technologies. Owing to their excellent biocompatibility, low immunogenicity, and adjustable mechanical properties, hydrogels are emerging as valuable tools in the reconstruction of organ function, supplemented by tissue engineering techniques to increase their structure and functionality. Hydrogel-based female reproductive reconstruction strategies targeting the pathological mechanisms of female infertility may provide alternatives for the treatment of ovarian, endometrium/uterine, and fallopian tube dysfunction. In this review, we provide a general introduction to the basic physiology and pathology of the female reproductive system, the limitations of current infertility treatments, and the lack of translation from animal models to human reproductive physiology. We further provide an overview of the current and future potential applications of hydrogels in the treatment of female reproductive system dysfunction, highlighting the great prospects of hydrogel-based strategies in the field of translational medicine, along with the significant challenges to be overcome.

PR-SET7 epigenetically restrains uterine interferon response and cell death governing proper postnatal stromal development

The differentiation of the stroma is a hallmark event during postnatal uterine development. However, the spatiotemporal changes that occur during this process and the underlying regulatory mechanisms remain elusive. Here, we comprehensively delineated the dynamic development of the neonatal uterus at single-cell resolution and characterized two distinct stromal subpopulations, inner and outer stroma. Furthermore, single-cell RNA sequencing revealed that uterine ablation of Pr-set7, the sole methyltransferase catalyzing H4K20me1, led to a reduced proportion of the inner stroma due to massive cell death, thus impeding uterine development. By combining RNA sequencing and epigenetic profiling of H4K20me1, we demonstrated that PR-SET7-H4K20me1 either directly repressed the transcription of interferon stimulated genes or indirectly restricted the interferon response via silencing endogenous retroviruses. Declined H4K20me1 level caused viral mimicry responses and ZBP1-mediated apoptosis and necroptosis in stromal cells. Collectively, our study provides insight into the epigenetic machinery governing postnatal uterine stromal development mediated by PR-SET7.

Single-Cell Sequencing Technology in Ruminant Livestock: Challenges and Opportunities

Advancements in single-cell sequencing have transformed the genomics field by allowing researchers to delve into the intricate cellular heterogeneity within tissues at greater resolution. While single-cell omics are more widely applied in model organisms and humans, their use in livestock species is just beginning. Studies in cattle, sheep, and goats have already leveraged single-cell and single-nuclei RNA-seq as well as single-cell and single-nuclei ATAC-seq to delineate cellular diversity in tissues, track changes in cell populations and gene expression over developmental stages, and characterize immune cell populations important for disease resistance and resilience. Although challenges exist for the use of this technology in ruminant livestock, such as the precise annotation of unique cell populations and spatial resolution of cells within a tissue, there is vast potential to enhance our understanding of the cellular and molecular mechanisms underpinning traits essential for healthy and productive livestock. This review intends to highlight the insights gained from published single-cell omics studies in cattle, sheep, and goats, particularly those with publicly accessible data. Further, this manuscript will discuss the challenges and opportunities of this technology in ruminant livestock and how it may contribute to enhanced profitability and sustainability of animal agriculture in the future.

Single-cell transcriptomic profiling of the neonatal oviduct and uterus reveals new insights into upper Müllerian duct regionalization

The upper Müllerian duct (MD) is patterned and specified into two morphologically and functionally distinct organs, the oviduct and uterus. It is known that this regionalization process is instructed by inductive signals from the adjacent mesenchyme. However, the interaction landscape between epithelium and mesenchyme during upper MD development remains largely unknown. Here, we performed single-cell transcriptomic profiling of mouse neonatal oviducts and uteri at the initiation of MD epithelial differentiation (postnatal day 3). We identified major cell types including epithelium, mesenchyme, pericytes, mesothelium, endothelium, and immune cells in both organs with established markers. Moreover, we uncovered region-specific epithelial and mesenchymal subpopulations and then deduced region-specific ligand-receptor pairs mediating mesenchymal-epithelial interactions along the craniocaudal axis. Unexpectedly, we discovered a mesenchymal subpopulation marked by neurofilaments with specific localizations at the mesometrial pole of both the neonatal oviduct and uterus. Lastly, we analyzed and revealed organ-specific signature genes of pericytes and mesothelial cells. Taken together, our study enriches our knowledge of upper MD development, and provides a manageable list of potential genes, pathways, and region-specific cell subtypes for future functional studies.

Single-cell transcriptomic profiling of the neonatal oviduct and uterus reveals new insights into upper Müllerian duct regionalization

The upper Müllerian duct (MD) is patterned and specified into two morphologically and functionally distinct organs, the oviduct and uterus. It is known that this regionalization process is instructed by inductive signals from the adjacent mesenchyme. However, the interaction landscape between epithelium and mesenchyme during upper MD development remains largely unknown. Here, we performed single-cell transcriptomic profiling of mouse neonatal oviducts and uteri at the initiation of MD epithelial differentiation (postnatal day 3). We identified major cell types including epithelium, mesenchyme, pericytes, mesothelium, endothelium, and immune cells in both organs with established markers. Moreover, we uncovered region-specific epithelial and mesenchymal subpopulations and then deduced region-specific ligand-receptor pairs mediating mesenchymal-epithelial interactions along the craniocaudal axis. Unexpectedly, we discovered a mesenchymal subpopulation marked by neurofilaments with specific localizations at the mesometrial pole of both the neonatal oviduct and uterus. Lastly, we analyzed and revealed organ-specific signature genes of pericytes and mesothelial cells. Taken together, our study enriches our knowledge of upper Müllerian duct development, and provides a manageable list of potential genes, pathways, and region-specific cell subtypes for future functional studies.