Argonaute proteins (Ago1–4) are essential components of the microRNA-induced silencing complex and play important roles in both microRNA biogenesis and function. Although Ago2 is the only one with the slicer activity, it is not clear whether the slicer activity is a universally critical determinant for Ago2's function in mammals. Furthermore, functional specificities associated with different Argonautes remain elusive. Here we report that microRNAs are randomly sorted to individual Argonautes in mammals, independent of the slicer activity. When both Ago1 and Ago2, but not either Ago1 or Ago2 alone, are ablated in the skin, the global expression of microRNAs is significantly compromised and it causes severe defects in skin morphogenesis. Surprisingly, Ago3 is able to load microRNAs efficiently in the absence of Ago1 and Ago2, despite a significant loss of global microRNA expression. Quantitative analyses reveal that Ago2 interacts with a majority of microRNAs (60%) in the skin, compared with Ago1 (30%) and Ago3 (<10%). This distribution is highly correlated with the abundance of each Argonaute, as quantified by shotgun proteomics. The quantitative correlation between Argonautes and their associated microRNAs is conserved in human cells. Finally, we measure the absolute expression of Argonaute proteins and determine that their copy number is ∼1.4 × 105 to 1.7 × 105 molecules per cell. Together, our results reveal a quantitative picture for microRNA activity in mammals.

Ling-zhi, a widely cultivated fungus in China, has a long history in traditional Chinese medicine. Although the name ‘Ganoderma lucidum’, a species originally described from England, has been applied to the fungus, their identities are not the same. This study aims to clarify the identity of this medicinally and economically important fungus. Specimens of Ling-zhi from China (field collections and cultivated basidiomata of the Chinese ‘G. lucidum’), G. lucidum from UK and other related Ganoderma species, were examined both morphologically and molecularly. High variability of basidioma morphology was found in the cultivated specimens of the Chinese ‘G. lucidum’, while some microscopic characters were more or less consistent, i.e. short clavate cutis elements, Bovista-type ligative hyphae and strongly echinulate basidiospores. These characters were also found in the holotype of G. sichuanense, a species originally described from Sichuan, China, and in recent collections made in the type locality of the species, which matched the diagnostic characters in the prologue. For comparison, specimens of closely related species, G. lucidum, G. multipileum, G. resinaceum, G. tropicum and G. weberianum, were also examined. DNA sequences were obtained from field collections, cultivated basidiomata and living strains of the Chinese ‘G. lucidum’, specimens from the type locality of G. sichuanense, and specimens of the closely related species studied. Three-gene combined analyses (ITS+IGS+rpb2) were performed and the results indicated that the Chinese ‘G. lucidum’ shared almost identical sequences with G. sichuanense. Based on both morphological and molecular data, the identity of the Chinese ‘G. lucidum’ (Ling-zhi) is considered conspecific with G. sichuanense. Detailed morphological descriptions and illustrations are provided in addition to discussion of nomenclature implications.

Background and Aims Nonalcoholic fatty liver disease (NAFLD) is characterized by accumulation of excessive triglycerides (TGs) in hepatocytes. Obesity is a major risk factor for developing fatty liver, although the intracellular molecular basis remains largely unclear. N6‐methyladenosine (m6A) RNA methylation is the most common internal modification in eukaryotic mRNA. Approach and Results In the present study, by m6A sequencing and RNA sequencing, we found that both m6A enrichment and mRNA expression of lipogenic genes were significantly increased in leptin‐receptor–deficient db/db mice. Importantly, our results showed that YT521‐B homology domain‐containing 2 (Ythdc2), an m6A reader, was markedly down‐regulated in livers of obese mice and NAFLD patients. Suppression of Ythdc2 in livers of lean mice led to TG accumulation, whereas ectopic overexpression of Ythdc2 in livers of obese mice improved liver steatosis and insulin resistance. Mechanistically, we found that Ythdc2 could bind to mRNA of lipogenic genes, including sterol regulatory element‐binding protein 1c, fatty acid synthase, stearoyl‐CoA desaturase 1, and acetyl‐CoA carboxylase 1, to decrease their mRNA stability and inhibit gene expression. Conclusions Our findings describe an important role of the m6A reader, Ythdc2, for regulation of hepatic lipogenesis and TG homeostasis, which might provide a potential target for treating obesity‐related NAFLD.

SUMMARYMicroRNAs (miRNAs) play important roles in differentiation of stem cells. However, the precise dynamics of miRNA induction during stem cell differentiation have not been visualized and molecular mechanisms through which miRNAs execute their function remain unclear. Using high-resolution in situ hybridization together with cell lineage and proliferation markers in mouse skin, we show that miR-203 is transcriptionally activated in the differentiating daughter cells upon the asymmetric cell division of interfollicular progenitor cells. Once induced, miR-203 rapidly promotes the cell cycle exit within 6 hours and abolishes self-renewal of the progenitor cells. With an inducible mouse model, we identify numerous miR-203 in vivo targets that are highly enriched in regulation of cell cycle and cell division, as well as in response to DNA damage. Importantly, co-suppression of individual targets, including p63, Skp2 and Msi2 by miR-203 is required for its function of promoting the cell cycle exit and inhibiting the long-term proliferation. Together, our findings reveal the rapid and widespread impact of miR-203 on the self-renewal program and provide mechanistic insights into the potent role of miR-203 during the epidermal differentiation. These results should also contribute to understanding the role of miR-203 in the development of skin cancer.