SummaryDue to differences across species, the mechanisms of cell fate decisions determined in mice cannot be readily extrapolated to humans. In this study, we developed a feeder- and xeno-free culture protocol that efficiently induced human pluripotent stem cells (iPSCs) into PLZF+/GPR125+/CD90+ spermatogonium-like cells (SLCs). These SLCs were enriched with key genes in germ cell development such as MVH, DAZL, GFRα1, NANOS3, and DMRT1. In addition, a small fraction of SLCs went through meiosis in vitro to develop into haploid cells. We further demonstrated that this chemically defined induction protocol faithfully recapitulated the features of compromised germ cell development of PSCs with NANOS3 deficiency or iPSC lines established from patients with non-obstructive azoospermia. Taken together, we established a powerful experimental platform to investigate human germ cell development and pathology related to male infertility.

Both circular RNAs (circRNAs) and cancer stem cells (CSCs) are separately known to be involved in cancer, but their interaction remains unclear. Here, the regulation of hepatocellular CSC self‐renewal is discovered by a circRNA, circ‐MALAT1, which is produced by back‐splicing of a long noncoding RNA, MALAT1. Circ‐MALAT1 is highly expressed in CSCs from clinical hepatocellular carcinoma samples under the mediation of an RNA‐binding protein, AUF1. Surprisingly, circMALAT1 functions as a brake in ribosomes to retard PAX5 mRNA translation and promote CSCs' self‐renewal by forming an unprecedented ternary complex with both ribosomes and mRNA. The discovered braking mechanism of a circRNA, termed mRNA braking, along with its more traditional role of miRNA sponging, uncovers a dual‐faceted pattern of circRNA‐mediated post‐transcriptional regulation for maintaining a specific cell state.

Cancer stem cells (CSCs) are the main cause of tumor development, metastasis, and relapse. CSCs are thus considered promising targets for cancer therapy. However, it is hard to eradicate CSCs due to their inherent plasticity and heterogeneity, and the underlying mechanism of the switch between non‐CSCs and CSCs remains unclear. Here, it is shown that miR‐135a combined with SMYD4 activates Nanog expression and induces the switch of non‐CSCs into CSCs. The miR‐135a level, once elevated, lowers the methylation level of the CG5 site in the Nanog promoter by directly targeting DNMT1. SMYD4 binds to the unmethylated Nanog promoter to activate Nanog expression in Nanog‐negative tumor cells. The in vivo regulation of miR‐135a levels could significantly affect both the CSCs proportion and tumor progression. These findings indicate that DNA methylation of the Nanog promoter modulates the switch of non‐CSCs into CSCs under the control of the miRNA‐135 level. In addition, the related pathways, miR‐135a/DNMT1 and SMYD4, involved in these processes are potential targets for CSC‐targeted therapy.

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Objective: Liver cancer stem cells (CSCs) are the culprits of hepatocellular carcinoma metastasis and recurrence. Only by eliminating tumor stem cells can malignant tumors be fundamentally cured. This study aimed to identify the role and underlying mechanism of aberrant Collagen Type XIV Alpha 1 Chain (COL14A1) overexpression in liver CSCs, and improve understanding of the molecular basis of hepatocellular carcinoma metastasis and recurrence. Methods: First, quantitative real-time polymerase chain reaction was used to confirm aberrant high-expression of COL14A1 in liver CSCs. Next, interference experiments were performed to determine the key role of COL14A1. To explore the mechanism of COL14A1 overexpression in liver CSCs, putative microRNA (miRNAs) targeting COL14A1 were analyzed using the miRTarBase database. Next, quantitative real-time polymerase chain reaction, western blotting, and luciferase reporter assays were performed to verify the interaction between miR-7108-3p and COL14A1. Lastly, key target proteins of the COL14A1-extracellular-regulated signal kinase (ERK) signaling pathway were identified through western blotting analysis. This study was approved by the Ethics Committee of Shanghai Fourth People's Hospital, Tongji University School of Medicine, China (approval No. 2019tjdx17) on February 21, 2019. Results: COL14A1 is abnormally highly expressed in liver CSCs, which is necessary for liver CSCs to maintain their self-renewal capability. Mechanistically, COL14A1 is post-transcriptionally regulated by miR-7108-3p in a negative manner. Low expression of miR-7108-3p increased translation of COL14A1, which subsequently activated ERK signaling, ultimately maintaining the self-renewal and stem cell-like properties of liver CSCs. Conclusion: COL14A1, which is negatively regulated by miR-7108-3p, was found to play a crucial role in maintaining the self-renewal and stem cell-like properties of liver CSCs through activation of ERK signaling.