LIF (leukaemia inhibitory factor) is a key cytokine for maintaining self-renewal and pluripotency of mESCs (mouse embryonic stem cells). Upon binding to the LIF receptor, LIF activates three major intracellular signalling pathways: the JAK (Janus kinase)/STAT3 (signal transducer and activator of transcription 3), PI3K (phosphoinositide 3-kinase)/AKT and SHP2 [SH2 (Src homology 2) domain-containing tyrosine phosphatase 2]/MAPK (mitogen-activated protein kinase) pathways. These pathways converge to orchestrate the gene expression pattern specific to mESCs. Among the many signalling events downstream of the LIF receptor, activation and DNA binding of the transcription factor STAT3 plays a central role in transducing LIF's functions. The fundamental role of LIF for pluripotency was highlighted further by the discovery that LIF accelerates the conversion of epiblast-derived stem cells into a more fully pluripotent state. In the present review, we provide an overview of the three major LIF signalling pathways, the molecules that interact with STAT3 and the current interpretations of the roles of LIF in pluripotency.

Nucleostemin is a nucleolar protein widely expressed in proliferating cells. Nucleostemin is involved in the regulation of cell proliferation, and both depletion and overexpression of nucleostemin induce cell cycle arrest through the p53 signaling pathway. Although the presence of p53-independent functions of nucleostemin has been previously suggested, the identities of these additional functions remained to be investigated. Here, we show that nucleostemin has a novel role as an integrated component of ribosome biogenesis, particularly pre-rRNA processing. Nucleostemin forms a large protein complex (>700 kDa) that co-fractionates with the pre-60 S ribosomal subunit in a sucrose gradient. This complex contains proteins related to pre-rRNA processing, such as Pes1, DDX21, and EBP2, in addition to several ribosomal proteins. We show that the nucleolar retention of DDX21 and EBP2 is dependent on the presence of nucleostemin in the nucleolus. Furthermore, the knockdown of nucleostemin delays the processing of 32 S pre-rRNA into 28 S rRNA. This is accompanied by a substantial decrease of protein synthesis as well as the levels of rRNAs and some mRNAs. In addition, overexpressed nucleostemin significantly promotes the processing of 32 S pre-rRNA. Collectively, these biochemical and functional studies demonstrate a novel role of nucleostemin in ribosome biogenesis. This is a key aspect of the role of nucleostemin in regulating cell proliferation.

Fibroblasts can be directly reprogrammed to cardiomyocyte-like cells by introducing defined genes. However, the reprogramming efficiency remains low, delaying the clinical application of this strategy to regenerative cardiology. We previously showed that fusion of the MyoD transactivation domain to the pluripotency transcription factor Oct4 facilitated the transcriptional activity of Oct4, resulting in highly efficient production of induced pluripotent stem cells. We examined whether the same approach can be applied to cardiac transcription factors to facilitate cardiac reprogramming. We fused the MyoD domain to Mef2c, Gata4, Hand2, and Tbx5 and transduced these genes in various combinations into mouse non-cardiac fibroblasts. Transduction of the chimeric Mef2c with the wild-types of the other three genes produced much larger beating clusters of cardiomyocyte-like cells faster than the combination of the four wild-type genes, with an efficiency of 3.5%, >15-fold greater than the wild-type genes. Fusion of a powerful transactivation domain to heterologous factors can increase the efficiency of direct reprogramming of fibroblasts to cardiomyocytes.

Induced pluripotent stem cell (iPSC) technology is a promising approach for converting one type of a differentiated cell into another type of differentiated cell through a pluripotent state as an intermediate step. Recent studies, however, indicate the possibility of directly converting one cell type to another without going through a pluripotent state. This direct reprogramming approach is dependent on a combination of highly potent transcription factors for cell-type conversion, presumably skipping more physiological and multi-step differentiation processes. A trial-and-error strategy is commonly used to screen many candidate transcription factors to identify the correct combination of factors. We speculate, however, that a better understanding of the functional mechanisms of exemplary transcriptional activators will facilitate the identification of novel factor combinations capable of direct reprogramming. The purpose of this review is to critically examine the literature on three highly potent transcriptional activators: the herpes virus protein, VP16; the master regulator of skeletal muscle differentiation, MyoD and the "pioneer" factor for hepatogenesis, FoxA. We discuss the roles of their functional protein domains, interacting partners and chromatin remodeling mechanisms during gene activation to understand how these factors open the chromatin of inactive genes and reset the transcriptional pattern during cell type conversion.

Induced pluripotent stem cells (iPSCs) can be created by reprogramming differentiated cells through introduction of defined genes, most commonly Oct4, Sox2, Klf4, and c‐Myc (OSKM). However, this process is slow and extremely inefficient. Here, we demonstrate radical acceleration of iPSC creation with a fusion gene between Oct4 and the powerful transactivation domain (TAD) of MyoD (M₃O). Transduction of M₃O as well as Sox2, Klf4, and c‐Myc into fibroblasts effectively remodeled patterns of DNA methylation, chromatin accessibility, histone modifications, and protein binding at pluripotency genes, raising the efficiency of making mouse and human iPSCs more than 50‐fold in comparison to OSKM. These results identified that one of the most critical barriers to iPSC creation is poor chromatin accessibility and protein recruitment to pluripotency genes. The MyoD TAD has a capability of overcoming this problem. Our approach of fusing TADs to unrelated transcription factors has far‐reaching implications as a powerful tool for transcriptional reprogramming beyond application to iPSC technology. STEM CELLS 2011; 29:1349–1361