Offspring production of ovarian organoids derived from spermatogonial stem cells by defined factors with chromatin reorganization

Epigenetic inheritance of acquired traits via stem cells dedifferentiation/differentiation or transdifferentiation cycles

Inheritance of acquired characteristics is the once widely accepted idea that multiple modifications acquired by an organism during its life, can be inherited by the offspring. This belief is at least as old as Hippocrates and became popular in early 19th century, leading Lamarck to suggest his theory of evolution. Charles Darwin, along with other thinkers of the time attempted to explain the mechanism of acquired traits' inheritance by proposing the theory of pangenesis. While later this and similar theories were rejected because of the lack of hard evidence, the studies aimed at revealing the mechanism by which somatic information can be passed to germ cells have continued up to the present. In this paper, we present a new theory and provide supporting literature to explain this phenomenon. We hypothesize existence of pluripotent adult stem cells that can serve as collectors and carriers of new epigenetic traits by entering different developmentally active organ/tissue compartments through blood circulation and acquiring new epigenetic marks though cycles of differentiation/dedifferentiation or transdifferentiation. During gametogenesis, these epigenetically modified cells are attracted by gonads, transdifferentiate into germ cells, and pass the acquired epigenetic modifications collected from the entire body's somatic cells to the offspring.

Knockdown H19 Accelerated iPSCs Reprogramming through Epigenetic Modifications and Mesenchymal-to-Epithelial Transition

H19 is an essential imprinted gene that is expressed to govern normal embryonic development. During reprogramming, the parental pronuclei have asymmetric reprogramming capacities and the critical reprogramming factors predominantly reside in the male pronucleus. After inhibiting the expression of H19 and Gtl2, androgenetic haploid ESCs (AG-haESCs) can efficiently and stably support the generation of healthy SC pups at a rate of ~20%, and double-knockout parthenogenetic haESCs can also produce efficiently. Induced pluripotent stem (iPS) cell reprogramming is thought to have a characteristic epigenetic pattern that is the reverse of its developmental potential; however, it is unclear how H19 participates in iPS cell reprogramming. Here, we showed that the expression of H19 was transiently increased during iPSC reprogramming. H19 knockdown resulted in greater reprogramming efficiency. The genes associated with pluripotency showed enhanced expression during the early reprogramming process, and the Oct4 promoter was demethylated by bisulfite genomic sequencing analysis. Moreover, expression analysis revealed that the mesenchymal master regulators associated with epithelial-to-mesenchymal transition (EMT) were downregulated during reprogramming in H19 knockdown. These findings provide functional insight into the role of H19 as a barrier to the early reprogramming process.

PLZF protein forms a complex with protein TET1 to target TCF7L2 in undifferentiated spermatogonia

The transcription factor promyelocytic leukemia zinc finger (PLZF, also known as ZBTB16) is critical for the self-renewal of spermatogonial stem cells (SSCs). However, the function of PLZF in SSCs is not clear. Here, we found that PLZF acted as an epigenetic regulator of stem cell maintenance and self-renewal of germ cells. The PLZF protein interacts with the ten-eleven translocation 1 (TET1) protein and subsequently acts as a modulator to regulate the expression of self-renewal-related genes. Furthermore, Transcription Factor 7-like 2 (TCF7L2) is promoted by the coordination of PLZF and Tri-methylation of lysine 4 on histone H3 (H3K4me3). In addition, testicular single-cell sequencing indicated that TCF7L2 is commonly expressed in the PLZF cluster. We demonstrated that PLZF directly targets TCF7L2 and alters the landscape of histone methylation in the SSCs nucleus. Meanwhile, the RD domain and Zn finger domain of PLZF synergize with H3K4me3 and directly upregulate TCF7L2 expression at the transcriptional level. Additionally, we identified a new association between PLZF and the histone methyltransferase EZH2 at the genomic level. Our study identified a new association between PLZF and H3K4me3, established the novel PLZF&TET1-H3K4me3-TCF7L2 axis at the genomic level which regulates undifferentiated spermatogonia, and provided a platform for studying germ cell development in male domestic animals.

Recent Progress of In Vitro 3D Culture of Male Germ Stem Cells

Male germline stem cells (mGSCs), also known as spermatogonial stem cells (SSCs), are the fundamental seed cells of male animal reproductive physiology. However, environmental influences, drugs, and harmful substances often pose challenges to SSCs, such as population reduction and quality decline. With advancements in bioengineering technology and biomaterial technology, an increasing number of novel cell culture methods and techniques have been employed for studying the proliferation and differentiation of SSCs in vitro. This paper provides a review on recent progress in 3D culture techniques for SSCs in vitro; we summarize the microenvironment of SSCs and spermatocyte development, with a focus on scaffold-based culture methods and 3D printing cell culture techniques for SSCs. Additionally, decellularized testicular matrix (DTM) and other biological substrates are utilized through various combinations and approaches to construct an in vitro culture microenvironment suitable for SSC growth. Finally, we present some perspectives on current research trends and potential opportunities within three areas: the 3D printing niche environment, alternative options to DTM utilization, and advancement of the in vitro SSC culture technology system.

Recent advances in endocrine organoids for therapeutic application

The endocrine system, consisting of the hypothalamus, pituitary, endocrine glands, and hormones, plays a critical role in hormone metabolic interactions. The complexity of the endocrine system is a significant obstacle to understanding and treating endocrine disorders. Notably, advances in endocrine organoid generation allow a deeper understanding of the endocrine system by providing better comprehension of molecular mechanisms of pathogenesis. Here, we highlight recent advances in endocrine organoids for a wide range of therapeutic applications, from cell transplantation therapy to drug toxicity screening, combined with development in stem cell differentiation and gene editing technologies. In particular, we provide insights into the transplantation of endocrine organoids to reverse endocrine dysfunctions and progress in developing strategies for better engraftments. We also discuss the gap between preclinical and clinical research. Finally, we provide future perspectives for research on endocrine organoids for the development of more effective treatments for endocrine disorders.

Prospects for fertility preservation: the ovarian organ function reconstruction techniques for oogenesis, growth and maturation in vitro

Today, fertility preservation is receiving more attention than ever. Cryopreservation, which preserves ovarian tissue to preserve fertility in young women and reduce the risk of infertility, is currently the most widely practiced. Transplantation, however, is less feasible for women with blood-borne leukemia or cancers with a high risk of ovarian metastasis because of the risk of cancer recurrence. In addition to cryopreservation and re-implantation of embryos, in vitro ovarian organ reconstruction techniques have been considered as an alternative strategy for fertility preservation. In vitro culture of oocytes in vitro Culture, female germ cells induction from pluripotent stem cells (PSC) in vitro, artificial ovary construction, and ovaria-related organoids construction have provided new solutions for fertility preservation, which will therefore maximize the potential for all patients undergoing fertility preservation. In this review, we discussed and thought about the latest ovarian organ function reconstruction techniques in vitro to provide new ideas for future ovarian disease research and fertility preservation of patients with cancer and premature ovarian failure.

Human organoid systems in modeling reproductive tissue development, function, and disease

Research focused on human reproductive biology has primarily relied upon clinical samples affording mainly descriptive studies with limited implementation of functional or mechanistic understanding. More importantly, restricted access to human embryonic material has necessitated the use of animals, primarily rats and mice, and short-term primary cell cultures derived from human patient material. While reproductive developmental processes are generally conserved across mammals, specific features unique to human reproduction have resulted in the development of human-based in vitro systems designed to retain or recapitulate key molecular and cellular processes important in humans. Of note, major advances in 3D epithelial stem cell-based systems modeling human reproductive organ development have been made. These cultures, broadly referred to as organoids, enable research aimed at understanding cellular hierarchies and processes controlling cellular differentiation and function. Moreover, organoids allow the pre-clinical testing of pharmacological substances, both from safety and efficacy standpoints, and hold large potential in driving aspects of personalized medicine that were previously not possible with traditional models. In this mini-review, we focus on summarizing the current state of regenerative organoid culture systems of the female and male reproductive tracts that model organ development, maintenance, and function. Specifically, we will introduce stem cell-based organoid models of the ovary/fallopian tube, endometrium, cervix, prostate gland, and testes. We will also describe organoid systems of the pre-implanting blastocyst and trophoblast, as the blastocyst and its extraembryonic trophectoderm are central to fetal, maternal, and overall pregnancy health. We describe the foundational studies leading to their development and outline the utility as well as specific limitations that are unique and common to many of these in vitro platforms.

YTHDF1 phase separation triggers the fate transition of spermatogonial stem cells by activating the IκB-NF-κB-CCND1 axis

N6-methyladenosine (m6A) modification controls cell fate determination. Here, we show that liquid-liquid phase separation (LLPS) of YTH N6-methyladenosine RNA binding protein 1 (YTHDF1), a pivotal m6A "reader" protein, promotes the transdifferentiation of spermatogonial stem cells (SSCs) into neural stem cell-like cells by activating the IκB-nuclear factor κB (NF-κB)-CCND1 axis. The inhibition of IκBα/β mRNA translation mediated by YTHDF1 LLPS is the key to the activation of the IκB-NF-κB-CCND1 axis. Disrupting either YTHDF1 LLPS or NF-κB activation inhibits transdifferentiation efficiency. Moreover, overexpression of the YTH domain of YTHDF1 inhibits the activation of the IκB-NF-κB-CCND1 axis by promoting IκBα/β mRNA translation. Overexpression of the tau-YTH fusion protein reactivates IκB-NF-κB-CCND1 axis by inhibiting the translation of IκBα/β mRNAs, and tau LLPS is observed, which can restore transdifferentiation efficiency. Our findings demonstrate that the protein-RNA LLPS plays essential roles in cell fate transition and provide insights into translational medicine and the therapy of neurological diseases.

Inhibition of EED activity enhances cell survival of female germline stem cell and improves the oocytes production during oogenesis in vitro

Ovarian organoids, based on female germline stem cells (FGSCs), are nowadays widely applied for reproductive medicine screening and exploring the potential mechanisms during mammalian oogenesis. However, there are still key issues that urgently need to be resolved in ovarian organoid technology, one of which is to establish a culture system that effectively expands FGSCs in vitro, as well as maintaining the unipotentcy of FGSCs to differentiate into oocytes. Here, FGSCs were EED226 treated and processed for examination of proliferation and differentiation in vitro. According to the results, EED226 specifically increased FGSC survival by decreasing the enrichment of H3K27me3 on Oct4 promoter and exon, as well as enhancing OCT4 expression and inhibiting P53 and P63 expression. Notably, we also found that FGSCs with EED226 treatment differentiated into more oocytes during oogenesis in vitro, and the resultant oocytes maintained a low level of P63 versus control at early stage development. These results demonstrated that inhibition of EED activity appeared to promote the survival of FGSCs and markedly inhibited their apoptosis during in vitro differentiation. As a result of our study, we propose an effective culture strategy to culture FGSCs and obtain oocytes in vitro, which provides a new vision for oogenesis in vitro.

Mechanistic insights into HuR inhibitor MS-444 arresting embryonic development revealed by low-input RNA-seq and STORM

With improvements in the survival rate of patients with cancer, fertility maintenance has become a major concern in terms of cancer treatment for women of reproductive age. Thus, it is important to examine the impact on fertility of anticancer drugs that are used clinically or are undergoing trials. The HuR small-molecule inhibitor MS-444 has been used in many cancer treatment studies, but its reproductive toxicity in females is unknown. Here, we reported that MS-444 blocked the nucleocytoplasmic transport of Agbl2 mRNA by inhibiting HuR dimerization, resulting in the developmental arrest of 2-cell stage embryos in mouse. Combining analysis of low-input RNA-seq for MS-444-treated 2-cell embryos and mapping binding sites of RNA-binding protein, Agbl2 was predicted to be the target gene of MS-444. For further confirmation, RNAi experiment in wild-type zygotes showed that Agbl2 knockdown reduced the proportion of embryos successfully developed to the blastocyst stage: from 71% in controls to 23%. Furthermore, RNA-FISH and luciferase reporter analyses showed that MS-444 blocked the nucleocytoplasmic transport of Agbl2 mRNA and reduced its stability by inhibiting HuR dimerization. In addition, optimized stochastic optical reconstruction microscopy (STORM) imaging showed that MS-444 significantly reduced the HuR dimerization, and HuR mainly existed in cluster form in 2-cell stage embryos. In conclusion, this study provides clinical guidance for maintaining fertility during the treatment of cancer with MS-444 in women of reproductive age. And also, our research provides guidance for the application of STORM in nanometer scale studies of embryonic cells. HuR inhibitor MS-444 arrested embryonic development at 2-cell stage. Low-input RNA-seq revealed that Agbl2 was the target gene of MS-444. MS-444 blocked the nucleocytoplasmic transport of Agbl2 mRNA by inhibiting HuR dimerization and reduced the stability of Agbl2 mRNA. STORM with our optimized protocol showed that HuR tended to form elliptical and dense clusters in 2-cell stage embryos.

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.

Comparative transcriptomics reveals circadian and pluripotency networks as two pillars of longevity regulation

Mammals differ more than 100-fold in maximum lifespan. Here, we conducted comparative transcriptomics on 26 species with diverse lifespans. We identified thousands of genes with expression levels negatively or positively correlated with a species' maximum lifespan (Neg- or Pos-MLS genes). Neg-MLS genes are primarily involved in energy metabolism and inflammation. Pos-MLS genes show enrichment in DNA repair, microtubule organization, and RNA transport. Expression of Neg- and Pos-MLS genes is modulated by interventions, including mTOR and PI3K inhibition. Regulatory networks analysis showed that Neg-MLS genes are under circadian regulation possibly to avoid persistent high expression, whereas Pos-MLS genes are targets of master pluripotency regulators OCT4 and NANOG and are upregulated during somatic cell reprogramming. Pos-MLS genes are highly expressed during embryogenesis but significantly downregulated after birth. This work provides targets for anti-aging interventions by defining pathways correlating with longevity across mammals and uncovering circadian and pluripotency networks as central regulators of longevity.

Three-dimensional genome structure shapes the recombination landscape of chromatin features during female germline stem cell development

BACKGROUND

During meiosis of mammalian cells, chromatin undergoes drastic reorganization. However, the dynamics of the three-dimensional (3D) chromatin structure during the development of female germline stem cells (FGSCs) are poorly understood.

METHODS

The high-throughput chromosome conformation capture technique was used to probe the 3D structure of chromatin in mouse germ cells at each stage of FGSC development.

RESULTS

The global 3D genome was dramatically reorganized during FGSC development. In topologically associating domains, the chromatin structure was weakened in germinal vesicle stage oocytes and still present in meiosis I stage oocytes but had vanished in meiosis II oocytes. This switch between topologically associating domains was related to the biological process of FGSC development. Moreover, we constructed a landscape of chromosome X organization, which showed that the X chromosome occupied a smaller proportion of the active (A) compartment than the autosome during FGSC development. By comparing the high-order chromatin structure between female and male germline development, we found that 3D genome organization was remodelled by two different potential mechanisms during gamete development, in which interchromosomal interactions, compartments, and topologically associating domain were decreased during FGSC development but reorganized and recovered during spermatogenesis. Finally, we identified conserved chromatin structures between FGSC development and early embryonic development.

CONCLUSIONS

These results provide a valuable resource to characterize chromatin organization and for further studies of FGSC development.

Retinoic acid induced meiosis initiation in female germline stem cells by remodelling three-dimensional chromatin structure

Objectives

This study aimed to clarify the regulation and mechanism of meiotic initiation in FGSC development.

Materials and Methods

FGSCs were induced to differentiate into meiosis in differentiation medium. RNA sequencing was performed to analysis the difference of transcription level. High‐through chromosome conformation capture sequencing (Hi‐C) was performed to analysis changes of three‐dimensional chromatin structure. Chromosome conformation capture further confirmed a spatial chromatin loop. ChIP‐qPCR and dual luciferase reporter were used to test the interaction between Stimulated by retinoic acid gene 8 (STRA8) protein and Trip13 promoter.

Results

Compared with FGSCs, the average diameter of STRA8‐positive germ cells increased from 13 μm to 16.8 μm. Furthermore, there were 4788 differentially expressed genes between the two cell stages; Meiosis and chromatin structure‐associated terms were significantly enriched. Additionally, Hi‐C results showed that FGSCs underwent A/B compartment switching (switch rate was 29.81%), the number of topologically associating domains (TADs) increasing, the average size of TADs decreasing, and chromatin loop changes at genome region of Trip13 from undifferentiated stage to meiosis‐initiation stage. Furthermore, we validated that Trip13 promoter contacted distal enhancer to form spatial chromatin loop and STRA8 could bind Trip13 promoter to promote gene expression.

Conclusion

FGSCs underwent chromatin structure remodelling from undifferentiated stage to meiosis‐initiation stage, which facilitated STRA8 binding to Trip13 promoter and promoting its expression.

Research Advances in Gametogenesis and Embryogenesis Using Pluripotent Stem Cells

The previous studies of human gametogenesis and embryogenesis have left many unanswered questions, which hinders the understanding of the physiology of these two vital processes and the development of diagnosis and treatment strategies for related diseases. Although many results have been obtained from animal studies, particularly mouse research, the results cannot be fully applied to humans due to species differences in physiology and pathology. However, due to ethical and material limitations, the direct study of human gametes and embryos is very difficult. The emergence and rapid development of organoids allow the construction of organoid systems that simulate gametogenesis and embryogenesis in vitro, and many studies have successfully established organoid systems for some parts of or even the entire processes of gametogenesis and embryogenesis. These studies typically start with the establishment of mouse models and then modify these models to obtain human organoid models. These organoid models can be used to obtain a better understanding of the signaling pathways, molecular mechanisms, genetics, and epigenetic changes involved in gametogenesis and embryogenesis and could also be applied to clinical applications, such as drug screening. Here, we discuss the formation of primordial stem cell-like cells (PGCLCs), and in vitro-induced gametes and embryoids using pluripotent stem cells (PSCs). We also analyze their applications and limitations.