The p53 transcription factor is a key tumor suppressor and a central regulator of the stress response. To ensure a robust and precise response to cellular signals,p53gene expression must be tightly regulated from the transcriptional to the post-translational levels. Computational predictions suggest that several microRNAs are involved in the post-transcriptional regulation ofp53. Here we demonstrate that miR-125b, a brain-enriched microRNA, is a bona fide negative regulator of p53 in both zebrafish and humans. miR-125b-mediated down-regulation of p53 is strictly dependent on the binding of miR-125b to a microRNA response element in the 3′ untranslated region ofp53mRNA. Overexpression of miR-125b represses the endogenous level of p53 protein and suppresses apoptosis in human neuroblastoma cells and human lung fibroblast cells. In contrast, knockdown of miR-125b elevates the level of p53 protein and induces apoptosis in human lung fibroblasts and in the zebrafish brain. This phenotype can be rescued significantly by either an ablation of endogenous p53 function or ectopic expression of miR-125b in zebrafish. Interestingly, miR-125b is down-regulated when zebrafish embryos are treated with γ-irradiation or camptothecin, corresponding to the rapid increase in p53 protein in response to DNA damage. Ectopic expression of miR-125b suppresses the increase of p53 and stress-induced apoptosis. Together, our study demonstrates that miR-125b is an important negative regulator of p53 and p53-induced apoptosis during development and during the stress response.

OBJECTIVE We investigated the regulation and involvement of microRNAs (miRNAs) in fat cell development and obesity.

Mesenchymal stem cells derived from human bone marrow (hBMSCs) and human adipose tissue (hAMSCs) represent a useful source of progenitor cells for cell therapy and tissue engineering. However, it is not clear what the similarities and differences between them are. Like hBMSCs, hAMSCs can differentiate into osteogenic, adipogenic, and chondrogenic cells. Whether MSCs derived from different tissue sources represent fundamentally similar or different cell types is not clear. Given the possible different sources of MSCs for cell therapy, a comprehensive comparison of the different MSCs would be very useful. Here, we compared the transcriptome profile of hAMCS and hBMSCs during directed differentiation into bone, cartilage, and fat. Our data revealed considerable similarities between bone marrow-derived MSCs (BMSCs) and adipose tissue-derived MSCs (AMSCs). We uncovered an interesting bifurcation of pathways in both BMSCs and AMSCs, in which osteogenesis and adipogenesis appear to be linked in a differentiation branch separate from chondrogenesis. Our data suggest that although a set of common genes may be needed for early differentiation into all three lineages, a different set of signature genes is associated with maturation into fully differentiated cells. The recruitment of different late differentiation factors explains and supports our conclusion that BMSCs differentiate more efficiently into bone and cartilage, whereas AMSCs differentiate better into adipocytes. This study not only generated a rich database for continuing molecular characterization of various MSCs but also provided a rational basis for assessing qualities of MSCs from different sources for the purpose of cell-based therapy and tissue engineering.

While much attention has been given to the study of different genetic and chemical methods for the generation of iPS (induced pluripotent stem) cell lines, relatively little is known about the variability in overall quality of iPS cells. This paper identifies a transcription factor, Tbx3, that significantly improves the quality of iPS cells. Tbx3 also accelerates the reprogramming process of mouse embryonic fibroblasts into iPS cells and significantly improves the germ-line transmission of iPS-derived germ cells in chimaeric animals. The transcription factor Tbx3 is shown to significantly improve the quality of induced pluripotent stem (iPS) cells. Tbx3 binding sites in embryonic stem cells are present in genes involved in pluripotency and reprogramming factors. Furthermore, there are intrinsic qualitative differences in iPS cells generated by different methods in terms of their pluripotency, thus highlighting the need to rigorously characterize iPS cells beyond in vitro studies. Induced pluripotent stem (iPS) cells can be obtained by the introduction of defined factors into somatic cells1. The combination of Oct4 (also known as Pou5f1), Sox2 and Klf4 (which we term OSK) constitutes the minimal requirement for generating iPS cells from mouse embryonic fibroblasts. These cells are thought to resemble embryonic stem cells (ESCs) on the basis of global gene expression analyses; however, few studies have tested the ability and efficiency of iPS cells to contribute to chimaerism, colonization of germ tissues, and most importantly, germ-line transmission and live birth from iPS cells produced by tetraploid complementation. Using genomic analyses of ESC genes that have roles in pluripotency and fusion-mediated somatic cell reprogramming, here we show that the transcription factor Tbx3 significantly improves the quality of iPS cells. iPS cells generated with OSK and Tbx3 (OSKT) are superior in both germ-cell contribution to the gonads and germ-line transmission frequency. However, global gene expression profiling could not distinguish between OSK and OSKT iPS cells. Genome-wide chromatin immunoprecipitation sequencing analysis of Tbx3-binding sites in ESCs suggests that Tbx3 regulates pluripotency-associated and reprogramming factors, in addition to sharing many common downstream regulatory targets with Oct4, Sox2, Nanog and Smad1. This study underscores the intrinsic qualitative differences between iPS cells generated by different methods, and highlights the need to rigorously characterize iPS cells beyond in vitro studies.

MicroRNAs (miRNAs) are a class of small noncoding RNAs that regulate gene expression at the posttranscriptional level. Research on miRNAs has highlighted their importance in neural development, but the specific functions of neurally enriched miRNAs remain poorly understood. We report here the expression profile of miRNAs during neuronal differentiation in the human neuroblastoma cell line SH-SY5Y. Six miRNAs were significantly upregulated during differentiation induced by all-trans-retinoic acid and brain-derived neurotrophic factor. We demonstrated that the ectopic expression of either miR-124a or miR-125b increases the percentage of differentiated SH-SY5Y cells with neurite outgrowth. Subsequently, we focused our functional analysis on miR-125b and demonstrated the important role of this miRNA in both the spontaneous and induced differentiations of SH-SH5Y cells. miR-125b is also upregulated during the differentiation of human neural progenitor ReNcell VM cells, and miR-125b ectopic expression significantly promotes the neurite outgrowth of these cells. To identify the targets of miR-125b regulation, we profiled the global changes in gene expression following miR-125b ectopic expression in SH-SY5Y cells. miR-125b represses 164 genes that contain the seed match sequence of the miRNA and/or that are predicted to be direct targets of miR-125b by conventional methods. Pathway analysis suggests that a subset of miR-125b-repressed targets antagonizes neuronal genes in several neurogenic pathways, thereby mediating the positive effect of miR-125b on neuronal differentiation. We have further validated the binding of miR-125b to the miRNA response elements of 10 selected mRNA targets. Together, we report here for the first time the important role of miR-125b in human neuronal differentiation.