The roles and regulation of Yes-associated protein 1 in stem cells

Yes-associated protein 1(YAP1)is a downstream effector of the Hippo signaling pathway,and it is involved in tumorigenesis,tissue repair,growth,and development.In this review,the biological roles and the mechanisms of YAP1 in mediating stem cell fate decisions are discussed,including cell proliferation,differentiation,and apoptosis.In general,YAP1 promotes the proliferation and differentiation of stem cells,including embryonic stem cells and adult stem cells.It inhibits apoptosis by binding to the transcription factors,e.g.,transcriptional enhanced associate domain(TEAD),Smad,runt-related transcription factor 1/2,p73,p63,and Erb84,to maintain tissue homeostasis.The translocalization of YAP1 in cellular nuclei and the phosphorylation in the cytoplasm work as important and unusual events for the activation of YAP1.Moreover,YAP1 serves as the crosstalk for the Hippo pathway and other signaling pathways,including the Wnt and Notch pathways.It is highlighted in this review that YAP1 is an essential regulator for stem cells that have significant applications in regenerative medicine and reproductive medicine.

Generation of male germ cells from induced pluripotent stem cells （iPS cells）： an in vitro and in vivo study

Recent studies have reported that induced pluripotent stem （iPS） cells from mice and humans can differentiate into primordial germ cells. However, whether iPS cells are capable of producing male germ cells is not known. The objective of this study was to investigate the differentiation potential of mouse iPS cells into spermatogonial stem cells and late-stage male germ cells. We used an approach that combines in vitrodifferentiation and in vivotransplantation. Embryoid bodies （EBs） were obtained from iPS cells using leukaemia inhibitor factor （LIF）-free medium. Quantitative PCR revealed a decrease in Oct4 expression and an increase in StraSand Vasa mRNA in the EBs derived from iPS cells, iPS cell-derived EBs were induced by retinoic acid to differentiate into spermatogonial stem cells （SSCs）, as evidenced by their expression of VASA, as well as CDH1 and GFRal, which are markers of SSCs. Furthermore, these germ cells derived from iPS cells were transplanted into recipient testes of mice that had been pre-treated with busulfan. Notably, iPS cell-derived SSCs were able to differentiate into male germ cells ranging from spermatogonia to round spermatids, as shown by VASA and SCP3 expression. This study demonstrates that iPS cells have the potential to differentiate into late-stage male germ cells. The derivation of male germ cells from iPS cells has potential applications in the treatment of male infertility and provides a model for uncovering the molecular mechanisms underlying male germ cell development.

Derivation of male germ cells from induced pluripotent stem （iPS） cells： a novel and crucial source for generating male gametes

One of the most significant findings in recent stem cell research is the establishment of the induced pluripotent stem （iPS） cells, because they could have critical implications in both regenerative and repro- ductive medicine. Male gametes play a crucial role in transmitting genetic information to subsequent generations, and notably there are more and more patients with azoospermia, due to genetic and environmental factors. Recent advancements on generation of male gametes from human iPS cells would bring great promise to produce patient own male gametes for treating male infertility and provide an excellent platform for unveiling molecular mechanisms of male germ cell development.

Generation of male germ cells in vitro from the stem cells

Infertility has become a serious disease since it affects 10%–15%of couples worldwide,and male infertility contributes to about 50%of the cases.Notably,a significant decrease occurs in the newborn population by 7.82 million in 2020 compared to 2016 in China.As such,it is essential to explore the effective methods of obtaining functional male gametes for restoring male fertility.Stem cells,including embryonic stem cells(ESCs),induced pluripotent stem cells(iPSCs),spermatogonial stem cells(SSCs),and mesenchymal stem cells(MSCs),possess the abilities of both self-renewal and differentiation into germ cells.Significantly,much progress has recently been achieved in the generation of male germ cells in vitro from various kinds of stem cells under the specified conditions,e.g.,the coculturing with Sertoli cells,three-dimensional culture system,the addition of growth factors and cytokines,and/or the overexpression of germ cell-related genes.In this review,we address the current advance in the derivation of male germ cells in vitro from stem cells based on the studies of the peers and us,and we highlight the perspectives and potential application of stem cell-derived male gametes in reproductive medicine.

The role of homozygous LOF variant of the PNLDC1 gene in oligo-astheno-teratozoospermia(OAT)and male infertility

Dear Editor,An interesting article from Zhao et al.recently published in Asian Journal of Andrology,has shown the association of a novel loss-of function(LOF)variant in PARN-like ribonuclease domain-containing exonuclease 1(PNLDCI)and male infertility,and we would like to contribute a commentary on this article.

OIP5 Interacts with NCK2 to Mediate Human Spermatogonial Stem Cell Self-Renewal and Apoptosis through Cell Cyclins and Cycle Progression and Its Abnormality Is Correlated with Male Infertility

Spermatogonial stem cells(SSCs)have important applications in both reproduction and regenerative medicine.Nevertheless,specific genes and signaling transduction pathways in mediating fate decisions of human SSCs remain elusive.Here,we have demonstrated for the first time that OIP5(Opa interacting protein 5)controlled the self-renewal and apoptosis of human SSCs.RNA sequencing identified that NCK2 was a target for OIP5 in human SSCs,and interestingly,OIP5 could interact with NCK2 as shown by Co-IP(co-immunoprecipitation),IP-MS(mass spectrometry),and GST pulldown assays.NCK2 silencing decreased human SSC proliferation and DNA synthesis but enhanced their apoptosis.Notably,NCK2 knockdown reversed the influence of OIP5 overexpression on human SSCs.Moreover,OIP5 inhibition decreased the numbers of human SSCs at S and G2/M phases,while the levels of numerous cell cycle proteins,including cyclins A2,B1,D1,E1 and H,especially cyclin D1,were remarkably reduced.Significantly,whole-exome sequencing of 777 patients with nonobstructive azoospermia(NOA)revealed 54 singlenucleotide polymorphism mutations of the OIP5 gene(6.95%),while the level of OIP5 protein was obviously lower in testes of NOA patients compared to fertile men.Collectively,these results implicate that OIP5 interacts with NCK2 to modulate human SSC self-renewal and apoptosis via cell cyclins and cell cycle progression and that its mutation and/or lower expression is correlated with azoospermia.As such,this study offers novel insights into molecular mechanisms underlying the fate determinations of human SSCs and the pathogenesis of NOA,and it provides new targets for treating male infertility.

Exosomes:key players in cancer and potential therapeutic strategy

Exosomes are extracellular vesicles secreted by most eukaryotic cells and participate in intercellular communication.The components of exosomes,including proteins,DNA,mRNA,microRNA,long noncoding RNA,circular RNA,etc.,which play a crucial role in regulating tumor growth,metastasis,and angiogenesis in the process of cancer development,and can be used as a prognostic marker and/or grading basis for tumor patients.Hereby,we mainly summarized as followed:the role of exosome contents in cancer,focusing on proteins and noncoding RNA;the interaction between exosomes and tumor microenvironment;the mechanisms that epithelial-mesenchymal transition,invasion and migration of tumor affected by exosomes;and tumor suppression strategies based on exosomes.Finally,the application potential of exosomes in clinical tumor diagnosis and therapy is prospected,which providing theoretical supports for using exosomes to serve precise tumor treatment in the clinic.

NODAL secreted by male germ cells regulates the proliferation and function of human Sertoli cells from obstructive azoospermia and nonobstructive azoospermia patients

This study was designed to explore the regulatory effects of male germ cell secreting factor NODAL on Sertoli cell fate decisions from obstructive azoospermia （OA） and nonobstructive azoospermia （NOA） patients. Human Sertoli cells and male germ cells were isolated using two-step enzymatic digestion and SATPUT from testes of azoospermia patients. Expression of NODAL and its multiple receptors in human Sertoli cells and male germ cells were characterized by reverse transcription-polymerase chain reaction （RT-PCRI and immunochemistry. Human recombinant NODAL and its receptor inhibitor SB431542 were employed to probe their effect on the proliferation of Sertoli cells using the CCK-8 assay. Quantitative PCR and Western blots were utilized to assess the expression of Sertoli cell functional genes and proteins. NODAL was found to be expressed in male germ cells but not in Sertoli cells, whereas its receptors ALK4, ALK7, and ACTR-IIB were detected in Sertoli cells and germ cells, suggesting that NODAL plays a regulatory role in Sertoli cells and germ cells via a paracrine and autocrine pathway, respectively. Human recombinant NODAL could promote the proliferation of human Sertoli cells. The expression of cell cycle regulators, including CYCLIN A, CYCLIN D1 and CYCLIN E, was not remarkably affected by NODAL signaling. NODAL enhanced the expression of essential growth factors, including GDNF, SCF, and BMP4, whereas SB431542 decreased their levels. There was not homogeneity of genes changes by NODAL treatment in Sertoli cells from OA and Sertoli cell-only syndrome （SCO） patients. Collectively, this study demonstrates that NODAL produced by human male germ cells regulates proliferation and numerous gene expression of Sertoli cells.

Plasticity of male germline stem cells and their applications in reproductive and regenerative medicine

Spermatogonial stem cells （SSCs）, also known as male germline stem cells, are a small subpopulation of type A spermatogonia with the potential of self-renewal to maintain stem cell pool and differentiation into spermatids in mammalian testis. SSCs are previously regarded as the unipotent stem cells since they can only give rise to sperm within the seminiferous tubules. However, this concept has recently been challenged because numerous studies have demonstrated that SSCs cultured with growth factors can acquire pluripotency to become embryonic stem-like cells. The in vivo and in vitro studies from peers and us have clearly revealed that SSCs can directly transdifferentiate into morphologic, phenotypic, and functional cells of other lineages. Direct conversion to the cells of other tissues has important significance for regenerative medicine. SSCs from azoospermia patients could be induced to differentiate into spermatids with fertilization and developmental potentials. As such, SSCs could have significant applications in both reproductive and regenerative medicine due to their unique and great potentials. In this review, we address the important plasticity of SSCs, with focuses on their self-renewal, differentiation, dedifferentiation, transdifferentiation, and translational medicine studies.

Characterization, isolation, and culture of spermatogonial stem cells in Macaca fascicularis

Spermatogonial stem cells(SSCs)have great applications in both reproductive and regenerative medicine.Primates including monkeys are very similar to humans with regard to physiology and pathology.Nevertheless,little is known about the isolation,the characteristics,and the culture of primate SSCs.This study was designed to identify,isolate,and culture monkey SSCs.Immunocytochemistry was used to identify markers for monkey SSCs.Glial cell line-derived neurotrophic factor family receptor alpha-1(GFRAl)-enriched spermatogonia were isolated from monkeys,namely Macaca fascicularis(M.fascicularis),by two-step enzymatic digestion and magnetic-activated cell sorting,and they were cultured on precoated plates in the conditioned medium.Reverse transcription-polymerase chain reaction(RT-PCR),immunocytochemistry,and RNA sequencing were used to compare phenotype and transcriptomes in GFRAl-enriched spermatogonia between 0 day and 14 days of culture,and xenotransplantation was performed to evaluate the function of GFRAl-enriched spermatogonia.SSCs shared some phenotypes with rodent and human SSCs.GFRAl-enriched spermatogonia with high purity and viability were isolated from M.fascicularis testes.The freshly isolated cells expressed numerous markers for rodent SSCs,and they were cultured for 14 days.The expression of numerous SSC markers was maintained during the cultivation of GFRAl-enriched spermatogonia.RNA sequencing reflected a 97.3%similarity in global gene profiles between 0 day and 14 days of culture.The xenotransplantation assay indicated that the GFRAl-enriched spermatogonia formed colonies and proliferated in vivo in the recipient c-Kitw/w(W)mutant mice.Collectively,GFRAl-enriched spermatogonia are monkey SSCs phenotypically both in vitro and in vivo.This study suggests that monkey might provide an alternative to human SSCs for basic research and application in human diseases.

Generation of functional organs from stem cells

We are now well entering the exciting era of stem cells.Potential stem cell therapy holds great promise for the treatment of many diseases such as stroke,traumatic brain injury,Alzheimer’s disease,Parkinson’s disease,amyotrophic lateral-sclerosis,myocardial infarction,muscular dystrophy,diabetes,and etc..It is generally believed that transplantation of specific stem cells into the injured tissue to replace the lost cells is an effective way to repair the tissue.In fact,organ transplantation has been successfully practiced in clinics for liver or kidney failure.However,the severe shortage of donor organs has been a major obstacle for the expansion of organ transplantation programs.Toward that direction,generation of transplantable organs using stem cells is a desirable approach for organ replacement and would be of great interest for both basic and clinical scientists.Here we review recent progress in the field of organ generation using various methods including single adult tissue stem cells,a blastocyst complementation system,tissue decellularization/recellularization and a combination of stem cells and tissue engineering.