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Summary Serotonin (5-HT) neurons, the major components of the raphe nuclei, arise from ventral hindbrain progenitors. Based on anatomical location and axonal projection, 5-HT neurons are coarsely divided into rostral and caudal groups. Here, we propose a novel strategy to generate hindbrain 5-HT neurons from human pluripotent stem cells (hPSCs), which involves the formation of ventral-type neural progenitor cells and stimulation of the hindbrain 5-HT neural development. A caudalizing agent, retinoid acid, was used to direct the cells into the hindbrain cell fate. Approximately 30%–40% of hPSCs successfully developed into 5-HT-expressing neurons using our protocol, with the majority acquiring a caudal rhombomere identity (r5–8). We further modified our monolayer differentiation system to generate 5-HT neuron-enriched hindbrain-like organoids. We also suggest downstream applications of our 5-HT monolayer and organoid cultures to study neuronal response to gut microbiota. Our methodology could become a powerful tool for future studies related to 5-HT neurotransmission., Graphical abstract, Highlights • Activation of SHH and RA signaling induces 5-HT neuronal fate from hPSCs • The generated 5-HT neurons have caudal hindbrain characteristics • Hindbrain-like organoids may form from hPSCs by activation of SHH and RA signaling • 5-HT neurons in monolayer and organoid culture can be used as a screening platform, In this article, Shim and colleagues show that the generation of caudal hindbrain-type 5-HT neurons as well as 5-HT-neuron-enriched hindbrain-like organoids can be achieved through the modulation of SHH and RA signaling in differentiating hPSCs. The authors further propose that these 5-HT neurons in a monolayer and organoid culture system could be utilized as a screening platform for small molecules that trigger the release of 5-HT.

The effects of some drugs, aging, cancers, and other diseases can cause muscle wasting. Currently, there are no effective drugs for treating muscle wasting. In this study, the effects of ginsenoside Rd (GRd) on muscle wasting were studied.Tumour necrosis factor-alpha (TNF-α)/interferon-gamma (IFN-γ)-induced myotube atrophy in mouse C2C12 and human skeletal myoblasts (HSkM) was evaluated based on cell thickness. Atrophy-related signalling, reactive oxygen species (ROS) level, mitochondrial membrane potential, and mitochondrial number were assessed. GRd (10 mg/kg body weight) was orally administered to aged mice (23-24 months old) and tumour-bearing (Lewis lung carcinoma [LLC1] or CT26) mice for 5 weeks and 16 days, respectively. Body weight, grip strength, inverted hanging time, and muscle weight were assessed. Histological analysis was also performed to assess the effects of GRd. The evolutionary chemical binding similarity (ECBS) approach, molecular docking, Biacore assay, and signal transducer and activator of transcription (STAT) 3 reporter assay were used to identify targets of GRd.GRd significantly induced hypertrophy in the C2C12 and HSkM myotubes (average diameter 50.8 ± 2.6% and 49.9% ± 3.7% higher at 100 nM, vs. control, P ≤ 0.001). GRd treatment ameliorated aging- and cancer-induced (LLC1 or CT26) muscle atrophy in mice, which was evidenced by significant increases in grip strength, hanging time, muscle mass, and muscle tissue cross-sectional area (1.3-fold to 4.6-fold, vs. vehicle, P ≤ 0.05; P ≤ 0.01; P ≤ 0.001). STAT3 was found to be a possible target of GRd by the ECBS approach and molecular docking assay. Validation of direct interaction between GRd and STAT3 was confirmed through Biacore analysis. GRd also inhibited STAT3 phosphorylation and STAT3 reporter activity, which led to the inhibition of STAT3 nuclear translocation and the suppression of downstream targets of STAT3, such as atrogin-1, muscle-specific RING finger protein (MuRF-1), and myostatin (MSTN) (29.0 ± 11.2% to 84.3 ± 30.5%, vs. vehicle, P ≤ 0.05; P ≤ 0.01; P ≤ 0.001). Additionally, GRd scavenged ROS (91.7 ± 1.4% reduction at 1 nM, vs. vehicle, P ≤ 0.001), inhibited TNF-α-induced dysregulation of ROS level, and improved mitochondrial integrity (P ≤ 0.05; P ≤ 0.01; P ≤ 0.001).GRd ameliorates aging- and cancer-induced muscle wasting. Our findings suggest that GRd may be a novel therapeutic agent or adjuvant for reversing muscle wasting.

Extracellular vesicles (EVs) are 50–300 nm vesicles secreted by eukaryotic cells. They can carry cargo (including miRNA) from the donor cell to the recipient cell. miRNAs in EVs can change the translational profile of the recipient cell and modulate cellular morphology. This endogenous mechanism has attracted the attention of the drug-delivery community in the last few years. EVs can be enriched with exogenous therapeutic miRNAs and used for treatment of diseases by targeting pathological recipient cells. However, there are some obstacles that need to be addressed before introducing therapeutic miRNA-enriched EVs in clinics. Here, we focused on the progress in the field of therapeutic miRNA enriched EVs, highlighted important areas where research is needed, and discussed the potential to use them as therapeutic miRNA carriers in the future.

Rationale : The Notch pathway stabilizes sprouting angiogenesis by favoring stalk cells over tip cells at the vascular front. Because tip and stalk cells have different properties in morphology and function, their transcriptional regulation remains to be distinguished. Transcription factor Sox17 is specifically expressed in endothelial cells, but its expression and role at the vascular front remain largely unknown. Objective : To specify the role of Sox17 and its relationship with the Notch pathway in sprouting angiogenesis. Methods and Results : Endothelial-specific Sox17 deletion reduces sprouting angiogenesis in mouse embryonic and postnatal vascular development, whereas Sox17 overexpression increases it. Sox17 promotes endothelial migration by destabilizing endothelial junctions and rearranging cytoskeletal structure and upregulates expression of several genes preferentially expressed in tip cells. Interestingly, Sox17 expression is suppressed in stalk cells in which Notch signaling is relatively high. Notch activation by overexpressing Notch intracellular domain reduces Sox17 expression both in primary endothelial cells and in retinal angiogenesis, whereas Notch inhibition by delta-like ligand 4 (Dll4) blockade increases it. The Notch pathway regulates Sox17 expression mainly at the post-transcriptional level. Furthermore, endothelial Sox17 ablation rescues vascular network from excessive tip cell formation and hyperbranching under Notch inhibition in developmental and tumor angiogenesis. Conclusions : Our findings demonstrate that the Notch pathway restricts sprouting angiogenesis by reducing the expression of proangiogenic regulator Sox17.

In human, Wnt/β-catenin signaling pathway plays a significant role in cell growth, cell development, and disease pathogenesis. Four human (Rspo)s are known to activate canonical Wnt/β-catenin signaling pathway. Presently, (Rspo)s serve as therapeutic target for several human diseases. Henceforth, basic understanding about the molecular properties of (Rspo)s is essential. We approached this issue by interpreting the biochemical and biophysical properties along with molecular evolution of (Rspo)s thorough computational algorithm methods. Our analysis shows that signal peptide length is roughly similar in (Rspo)s family along with similarity in aa distribution pattern. In Rspo3, four N-glycosylation sites were noted. All members are hydrophilic in nature and showed alike GRAVY values, approximately. Conversely, Rspo3 contains the maximum positively charged residues while Rspo4 includes the lowest. Four highly aligned blocks were recorded through Gblocks. Phylogenetic analysis shows Rspo4 is being rooted with Rspo2 and similarly Rspo3 and Rspo1 have the common point of origin. Through phylogenomics study, we developed a phylogenetic tree of sixty proteins (n=60) with the orthologs and paralogs seed sequences. Protein-protein network was also illustrated. Results demonstrated in our study may help the future researchers to unfold significant physiological and therapeutic properties of (Rspo)s in various disease models.

Recently, the R-spondin (RSPO) family of proteins has emerged as important regulators of WNT signaling. Considering the wide spectrum of WNT signaling functions in normal biological processes and disease conditions, there has been a significantly growing interest in understanding the functional roles of RSPOs in multiple biological processes and determining the molecular mechanisms by which RSPOs regulate the WNT signaling pathway. Recent advances in the RSPO research field revealed some of the in vivo functions of RSPOs and provided new information regarding the mechanistic roles of RSPO activity in regulation of WNT signaling. Herein, we review recent progress in RSPO research with an emphasis on signaling mechanisms and biological functions.

R-spondins (RSPOs) are a family of cysteine-rich secreted proteins containing a single thrombospondin type I repeat (TSR) domain. A vast amount of information regarding cellular signaling and biological functions of RSPOs has emerged over the last several years, especially with respect to their roles in the activation of the WNT signaling pathway. The identification of several classes of RSPO receptors may indicate that this family of proteins can affect several signaling cascades. Herein, we summarize the current understanding of RSPO signaling and its biological functions, and discuss its potential therapeutic implications to human diseases.

R-spondins (RSPOs) are a recently characterized family of secreted proteins that activate WNT/β-catenin signaling. In this study, we investigated the potential roles of the RSPO proteins during myogenic differentiation. Overexpression of the Rspo1 gene or administration of recombinant RSPO2 protein enhanced mRNA and protein expression of a basic helix-loop-helix (bHLH) class myogenic determination factor, MYF5, in both C2C12 myoblasts and primary satellite cells, whereas MYOD or PAX7 expression was not affected. RSPOs also promoted myogenic differentiation and induced hypertrophic myotube formation in C2C12 cells. In addition, Rspo2 and Rspo3 gene knockdown by RNA interference significantly compromised MYF5 expression, myogenic differentiation, and myotube formation. Furthermore, Myf5 expression was reduced in the developing limbs of mouse embryos lacking the Rspo2 gene. Finally, we demonstrated that blocking of WNT/β-catenin signaling by DKK1 or a dominant-negative form of TCF4 reversed MYF5 expression, myogenic differentiation, and hypertrophic myotube formation induced by RSPO2, indicating that RSPO2 exerts its activity through the WNT/β-catenin signaling pathway. Our results provide strong evidence that RSPOs are key positive regulators of skeletal myogenesis acting through the WNT/β-catenin signaling pathway.

Recently, we reported that mutations in the R-spondin 4 (RSPO4) gene underlie inherited anonychia/hyponychia. Here, we studied five consanguineous Pakistani families with recessive inheritance of a combination of anonychia and hyponychia. Homozygous mutations were identified in the RSPO4 gene in all five families. Three families had a splice site mutation at the exon 2-intron 2 boundary. One family had a 26 bp deletion encompassing the start codon, and the final family had a missense mutation changing the initiating methionine to isoleucine. We demonstrated by in situ hybridization that Rspo4 is exclusively expressed in the mesenchyme underlying the digit tip epithelium in the mouse at embryonic day 14.5 (e14.5). These findings expand our understanding of the role of RSPO4 in nail development and disease.

The N-end rule relates the in vivo half-life of a protein to the identity of its N-terminal residue. The N-end rule pathway is one proteolytic pathway of the ubiquitin system. The recognition component of this pathway, called N-recognin or E3, binds to a destabilizing N-terminal residue of a substrate protein and participates in the formation of a substrate-linked multiubiquitin chain. We report the cloning of the mouse and human Ubr1 cDNAs and genes that encode a mammalian N-recognin called E3α. Mouse UBR1p (E3α) is a 1,757-residue (200-kDa) protein that contains regions of sequence similarity to the 225-kDa Ubr1p of the yeast Saccharomyces cerevisiae . Mouse and human UBR1p have apparent homologs in other eukaryotes as well, thus defining a distinct family of proteins, the UBR family. The residues essential for substrate recognition by the yeast Ubr1p are conserved in the mouse UBR1p. The regions of similarity among the UBR family members include a putative zinc finger and RING-H2 finger, another zinc-binding domain. Ubr1 is located in the middle of mouse chromosome 2 and in the syntenic 15q15-q21.1 region of human chromosome 15. Mouse Ubr1 spans ≈120 kilobases of genomic DNA and contains ≈50 exons. Ubr1 is ubiquitously expressed in adults, with skeletal muscle and heart being the sites of highest expression. In mouse embryos, the Ubr1 expression is highest in the branchial arches and in the tail and limb buds. The cloning of Ubr1 makes possible the construction of Ubr1 -lacking mouse strains, a prerequisite for the functional understanding of the mammalian N-end rule pathway.

While activation of the Notch pathway is observed in many human cancers, it is unknown whether elevated Notch1 expression is sufficient to initiate tumorigenesis in most tissues. To test the oncogenic potential of Notch1 in solid tumors, we expressed an activated form of Notch1 (N1ICD) in the developing mouse brain. N1ICD;hGFAP-cre mice were viable but developed severe ataxia and seizures, and died by weaning age. Analysis of transgenic embryo brains revealed that N1ICD expression induced p53-dependent apoptosis. When apoptosis was blocked by genetic deletion of p53, 30% to 40% of N1ICD;GFAP-cre;p53+/− and N1ICD;GFAP-cre;p53−/− mice developed spontaneous medulloblastomas. Interestingly, N1ICD-induced medulloblastomas most closely resembled the sonic hedgehog subgroup of human medulloblastoma at the molecular level. Surprisingly, N1ICD-induced tumors do not maintain high levels of the Notch pathway gene expression, except for Notch2, showing that initiating oncogenic events may not be decipherable by analyzing growing tumors in some cases. In summary, this study shows that Notch1 has an oncogenic potential in the brain when combined with other oncogenic hits, such as p53 loss, and provides a novel mouse model of medulloblastoma. Cancer Res; 73(17); 5381–90. ©2013 AACR.

Wnt signaling plays critical biological roles during normal embryonic development and homeostasis in adults. In the canonical pathway, binding of Wnt ligands to the Frizzled (Fzd) receptor and the low density lipoprotein-related receptor (LRP) 5 or LRP6 coreceptor initiates downstream signaling events leading to gene activation by beta-catenin and the T-cell factor (TCF)-lymphoid enhancer factor (LEF) family transcription factor complex. In this study, we provide several lines of evidence that the mouse Cristin/R-spondin family proteins function as Fzd8 and LRP6 receptor ligands and induce the canonical Wnt/beta-catenin signaling pathway, leading to TCF-dependent gene activation. First, conditioned medium containing Cristin/R-spondin proteins effectively induced reporter activity in a TCF-binding site-dependent manner. Second, stimulation of cells with Cristin/R-spondin was accompanied by stabilization of endogenous beta-catenin proteins and induction of canonical Wnt target genes. Third, Cristin/R-spondin proteins physically interacted with the extracellular domains of the LRP6 and Fzd8 receptors in vivo and in vitro. Interestingly, unlike canonical Wnt ligands, Cristin/R-spondin failed to form a ternary complex with both LRP6 and Fzd8 receptors, suggesting that R-spondin may activate the canonical Wnt signaling pathway by different mechanisms. Furthermore, Cristin/R-spondin proteins possess an intriguing positive modulatory activity on Wnt ligands, possibly through a direct interaction. Our findings expand the repertoire of ligands that induce beta-catenin/TCF-dependent gene activation and implicate the presence of active beta-catenin-dependent gene activation in a Wnt-free biological context.