Cells responding to hedgehog signaling contribute to the theca of ovarian follicles

A single-nucleus transcriptomic atlas characterizes cell types and their molecular features in the ovary of adult Nile tilapia

In fish species, there is limited analysis of signature transcriptome profiles at the single-cell level in gonadal cells. Here, the molecular signatures of distinct ovarian cell categories in adult Nile tilapia (Oreochromis niloticus) were analysed using single-nucleus RNA sequencing (snRNA-seq). We identified four cell types (oogonia, oocytes, granulosa cell, and thecal cell) based on their specifically expressed genes and biological functions. Similarly, we found some key pathways involved in ovarian development that may affect germline-somatic interactions. A cell-to-cell communication network between the distinct cell types was constructed. We found that the bidirectional communication is mandatory for the development of germ cells and somatic cells in fish ovaries, and the granulosa cells and thecal cells play a central regulating role in the cell network in fish ovary. Additionally, we identified some novel candidate marker genes for various types of ovarian cells and also validated them using in situ hybridization. Our work reveals an ovarian atlas at the cellular and molecular levels and contributes to providing insights into oogenesis and gonad development in fish.

Three-dimensional culture in a bioengineered matrix and somatic cell complementation to improve growth and survival of bovine preantral follicles

Purpose

Here we explored poly(ethylene glycol) (PEG) bioengineered hydrogels for bovine preantral follicle culture with or without ovarian cell co-culture and examined the potential for differentiation of bovine embryonic stem cells (bESCs) towards gonadal somatic cells to develop a system more similar to the ovarian microenvironment.

Methods

Bovine preantral follicles were first cultured in two-dimensional (2D) control or within PEG hydrogels (3D) and then co-cultured within PEG hydrogels with bovine ovarian cells (BOCs) to determine growth and viability. Finally, we tested conditions to drive differentiation of bESCs towards the intermediate mesoderm and bipotential gonad fate.

Results

Primary follicles grew over the 10-day culture period in PEG hydrogels compared to 2D control. Early secondary follicles maintained a similar diameter within the PEG while control follicles decreased in size. Follicles lost viability after co-encapsulation with BOCs; BOCs lost stromal cell signature over the culture period within hydrogels. Induction of bESCs towards gonadal somatic fate under WNT signaling was sufficient to upregulate intermediate mesoderm ( LHX1 ) and early coelomic epithelium/bipotential gonad markers ( OSR1 , GATA4 , WT1 ). Higher BMP4 concentrations upregulated the lateral plate mesoderm marker FOXF1 . PAX3 expression was not induced, indicating absence of the paraxial mesoderm lineage.

Conclusions

Culture of primary stage preantral follicles in PEG hydrogels promoted growth compared to controls; BOCs did not maintain identity in the PEG hydrogels. Collectively, we demonstrate that PEG hydrogels can be a potential culture system for early preantral follicles pending refinements, which could include addition of ESC-derived ovarian somatic cells using the protocol described here.

CAPSULE SUMMARY

We demonstrate that three-dimensional bioengineered hydrogels could aid in the survival and growth of small bovine preantral follicles. Moreover, bovine embryonic stem cells have the potential to differentiate towards precursors of somatic gonadal cell types, presenting an alternative cell source for preantral follicle co-culture.

Unveiling the Differentiation Potential of Ovarian Theca Interna Cells from Multipotent Stem Cell-like Cells

RESEARCH QUESTION

Theca interna cells (TICs) are an indispensable cell source for ovarian follicle development and steroidogenesis. Recent studies have identified theca stem cells (TSCs) in both humans and animals. Interestingly, TSCs express mesenchymal stem cell (MSC)-related markers and can differentiate into mesenchymal lineages. MSCs are promising for tissue engineering and regenerative medicine due to their self-renewal and differentiation abilities. Therefore, this study investigated the potential origin of TICs from MSCs.

DESIGN

Whole ovaries from postmenopausal organ donors were obtained, and their cortex was cryopreserved prior to the isolation of stromal cells. These isolated cells were differentiated in vitro to TICs using cell media enriched with various growth factors and hormones. Immunocytochemistry, an enzyme-linked immunosorbent assay, flow cytometry, and reverse transcription-quantitative polymerase chain were employed at different timepoints. Data were analyzed using one-way ANOVA.

RESULTS

Immunocytochemistry showed an increase in TIC markers from day 0 to day 8 and a significant rise in MSC-like markers on day 2. This corresponds with rising androstenedione levels from day 2 to day 13. Flow cytometry identified a decreasing MSC-like cell population from day 2 onwards. The CD13+ cell population and its gene expression increased significantly over time. NGFR and PDGFRA expression was induced on days 0 and 2, respectively, compared to day 13.

CONCLUSIONS

This study offers insights into MSC-like cells as the potential origin of TICs. Differentiating TICs from these widely accessible MSCs holds potential significance for toxicity studies and investigating TIC-related disorders like polycystic ovary syndrome (PCOS).

Analyzing the cellular and molecular atlas of ovarian mesenchymal cells provides a strategy against female reproductive aging

Ovarian mesenchymal cells (oMCs) constitute a distinct microenvironment that supports folliculogenesis under physiological conditions. Supplementation of exogenous non-ovarian mesenchymal-related cells has been reported to be an efficient approach to improve ovarian functions. However, the development and cellular and molecular characteristics of endogenous oMCs remain largely unexplored. In this study, we surveyed the single-cell transcriptomic landscape to dissect the cellular and molecular changes associated with the aging of oMCs in mice. Our results showed that the oMCs were composed of five ovarian differentiated MC (odMC) populations and one ovarian mesenchymal progenitor (oMP) cell population. These cells could differentiate into various odMCs via an oMP-derived route to construct the ovarian stroma structures. Comparative analysis revealed that ovarian aging was associated with decreased quantity of oMP cells and reduced quality of odMCs. Based on the findings of bioinformatics analysis, we designed different strategies involving supplementation with young oMCs to examine their effects on female fertility and health. Our functional investigations revealed that oMCs supplementation prior to ovarian senescence was the optimal method to improve female fertility and extend the reproductive lifespan of aged females in the long-term.

The characterization and therapeutic applications of ovarian theca cells: An update

Theca cells perform a range of roles during folliculogenesis. So far, little is known about their recruitment process and function since early research has mainly focused on the interactions between granulosa cells and the oocyte, leaving theca cells unfairly forgotten in the understanding of ovarian physiology and pathogenesis. Given that research on theca cells has greatly emerged in recent years, this review of literature aims to discuss the established theoretical concepts with the most recent findings about theca cells' characterization and origins, in vitro culture applications as models for fertility preservation and pharmacological/toxicological studies, its importance in unraveling pathogenic pathways, and stem-cell-based bioengineering for hormonal replacement therapies. Isolation and in vitro culture techniques for theca cells have led to essential advancements in their characterization as a specific cell population. Unraveling the origins of theca cells during the in vivo differentiation process in the adult ovary will assist the development of hormonal replacement therapies, reestablishment of fertility, and treatments for diseases such as premature ovarian insufficiency and polycystic ovarian syndrome, which seem to be directly influenced by theca cells.

Application of Single-Cell RNA Sequencing in Ovarian Development

The ovary is a female reproductive organ that plays a key role in fertility and the maintenance of endocrine homeostasis, which is of great importance to women's health. It is characterized by a high heterogeneity, with different cellular subpopulations primarily containing oocytes, granulosa cells, stromal cells, endothelial cells, vascular smooth muscle cells, and diverse immune cell types. Each has unique and important functions. From the fetal period to old age, the ovary experiences continuous structural and functional changes, with the gene expression of each cell type undergoing dramatic changes. In addition, ovarian development strongly relies on the communication between germ and somatic cells. Compared to traditional bulk RNA sequencing techniques, the single-cell RNA sequencing (scRNA-seq) approach has substantial advantages in analyzing individual cells within an ever-changing and complicated tissue, classifying them into cell types, characterizing single cells, delineating the cellular developmental trajectory, and studying cell-to-cell interactions. In this review, we present single-cell transcriptome mapping of the ovary, summarize the characteristics of the important constituent cells of the ovary and the critical cellular developmental processes, and describe key signaling pathways for cell-to-cell communication in the ovary, as revealed by scRNA-seq. This review will undoubtedly improve our understanding of the characteristics of ovarian cells and development, thus enabling the identification of novel therapeutic targets for ovarian-related diseases.

Germline stem cells in human

The germline cells are essential for the propagation of human beings, thus essential for the survival of mankind. The germline stem cells, as a unique cell type, generate various states of germ stem cells and then differentiate into specialized cells, spermatozoa and ova, for producing offspring, while self-renew to generate more stem cells. Abnormal development of germline stem cells often causes severe diseases in humans, including infertility and cancer. Primordial germ cells (PGCs) first emerge during early embryonic development, migrate into the gentile ridge, and then join in the formation of gonads. In males, they differentiate into spermatogonial stem cells, which give rise to spermatozoa via meiosis from the onset of puberty, while in females, the female germline stem cells (FGSCs) retain stemness in the ovary and initiate meiosis to generate oocytes. Primordial germ cell-like cells (PGCLCs) can be induced in vitro from embryonic stem cells or induced pluripotent stem cells. In this review, we focus on current advances in these embryonic and adult germline stem cells, and the induced PGCLCs in humans, provide an overview of molecular mechanisms underlying the development and differentiation of the germline stem cells and outline their physiological functions, pathological implications, and clinical applications.

Deciphering Sex-Specific Differentiation of Human Fetal Gonads: Insight From Experimental Models

Sex-specific gonadal differentiation is initiated by the expression of SRY in male foetuses. This promotes a signalling pathway directing testicular development, while in female foetuses the absence of SRY and expression of pro-ovarian factors promote ovarian development. Importantly, in addition to the initiation of a sex-specific signalling cascade the opposite pathway is simultaneously inhibited. The somatic cell populations within the gonads dictates this differentiation as well as the development of secondary sex characteristics via secretion of endocrine factors and steroid hormones. Opposing pathways SOX9/FGF9 (testis) and WNT4/RSPO1 (ovary) controls the development and differentiation of the bipotential mouse gonad and even though sex-specific gonadal differentiation is largely considered to be conserved between mice and humans, recent studies have identified several differences. Hence, the signalling pathways promoting early mouse gonad differentiation cannot be directly transferred to human development thus highlighting the importance of also examining this signalling in human fetal gonads. This review focus on the current understanding of regulatory mechanisms governing human gonadal sex differentiation by combining knowledge of these processes from studies in mice, information from patients with differences of sex development and insight from manipulation of selected signalling pathways in ex vivo culture models of human fetal gonads.

New Sex Chromosomes in Lake Victoria Cichlid Fishes (Cichlidae: Haplochromini)

African cichlid fishes harbor an extraordinary diversity of sex-chromosome systems. Within just one lineage, the tribe Haplochromini, at least 6 unique sex-chromosome systems have been identified. Here we focus on characterizing sex chromosomes in cichlids from the Lake Victoria basin. In Haplochromis chilotes, we identified a new ZW system associated with the white blotch color pattern, which shows substantial sequence differentiation over most of LG16, and is likely to be present in related species. In Haplochromis sauvagei, we found a coding polymorphism in amh that may be responsible for an XY system on LG23. In Pundamilia nyererei, we identified a feminizing effect of B chromosomes together with XY- and ZW-patterned differentiation on LG23. In Haplochromis latifasciatus, we identified a duplication of amh that may be present in other species of the Lake Victoria superflock. We further characterized the LG5-14 XY system in Astatotilapia burtoni and identified the oldest stratum on LG14. This species also showed ZW differentiation on LG2. Finally, we characterized an XY system on LG7 in Astatoreochromis alluaudi. This report brings the number of distinct sex-chromosome systems in haplochromine cichlids to at least 13, and highlights the dynamic evolution of sex determination and sex chromosomes in this young lineage.