Journal of Molecular Cell Biology - Advance Access

Generation of Homogeneous PDX1+ Pancreatic Progenitors from Human ES Cell-derived Endoderm Cells

Thu, 12 Nov 2009 04:07:04 PST

One key step in producing insulin-secreting cells from human embryonic stem (hES) cells is the generation of pancreatic and duodenal homeobox gene 1 (PDX1)-expressing pancreatic progenitor cells. All-trans retinoic acid (RA) has important roles in pancreas development and is widely used to induce pancreatic differentiation of ES cells. When RA was added directly to the activin A-induced hES cells, <20% cells were positive for the pancreatic marker PDX1, whereas the other cells were mainly hepatic cells. We found that when the activin A-induced hES cells were replated and seeded at low cell densities, the addition of RA induced significant pancreatic differentiation and over 70% of cells in culture expressed PDX1. When the endodermal cells were isolated with the surface marker CXCR4 from the activin A-induced culture and further differentiated with RA, a homogeneous PDX1⁺ cell population (over 95% pure) was generated. The PDX1⁺ cells could further differentiate into cells that expressed pancreatic transcription factors and pancreatic endocrine or exocrine markers. We also found that RA inhibited the hepatic differentiation of endodermal cells that were seeded at low cell densities, and this inhibition may have been through the inhibition of Smad1/5/8 activity. Thus, we present a highly efficient and reproducible protocol for generating PDX1⁺ pancreatic progenitor cells from hES cells.

Direct Activation of Protein Kinases by Ubiquitin

Baker, R., Ghosh, S. — Wed, 21 Oct 2009 03:07:22 PDT

The inhibitor of kB kinase (IKK) complex, a critical positive regulator of nuclear factor B (NF-B) signaling and immune function, can be activated in vitro by polyubiquitin chains. The modification of signaling intermediates by polyubiquitin and their association with ubiquitin-binding domain-containing proteins within multimolecular signaling complexes therefore represent a potential mechanism for activation of IKK and NF-B in vivo.

Sensorium: The Original Raison D'etre of the Motile Cilium?

Quarmby, L. M., Leroux, M. R. — Fri, 16 Oct 2009 01:12:03 PDT

The role of non-motile (primary) cilia as sensory antennae critical for metazoan development and physiology has surfaced over the last decade, long after the function of motile cilia in propelling cells or moving fluids across tissues was well established. A new study of motile cilia from respiratory airways raises the possibility that transducing sensory cues from the environment is a universal characteristic of cilia and may have been the original raison d'être of the ancestral cilium.

Type I and Type II Pathways of Fas-mediated Apoptosis Are Differentially Controlled by XIAP

Hao, Z., Mak, T. W. — Fri, 16 Oct 2009 01:12:02 PDT

The mechanism by which Fas activates the apoptotic pathway differs in so-called type I and type II cells. X chromosome-linked inhibitor of apoptosis protein has now been revealed as an important molecule that is differentially regulated in type I vs. type II cells.

Shifting in Balance Between Osteogenesis and Adipogenesis Substantially Influences Hematopoiesis

Sugimura, R., Li, L. — Wed, 14 Oct 2009 23:26:26 PDT

Adipocytes have been viewed as a space-filler in bone marrow for a long time. However, a recent study (Naveiras et al., 2009. Nature 460, 259–263) shows that adipocytes are microenvironmental components that suppress hematopoiesis under homeostatic and especially stressed conditions.

The Engineering of Brown Fat

Christian, M., Parker, M. G. — Mon, 12 Oct 2009 23:29:51 PDT

The developmental origins of brown adipose tissue and white adipose tissue are distinct, with brown adipocytes being derived from muscle precursors. PR domain containing 16, together with C/EBPβ, forms a lineage-switching transcriptional complex which promotes brown fat differentiation and suppresses muscle cell differentiation.

Rapamycin: The Cure for all that Ails

Hasty, P. — Sun, 04 Oct 2009 23:53:11 PDT

Target of rapamycin (TOR) signaling stimulates cell growth by regulating protein synthesis in response to a variety of stimuli in a wide range of species and is inhibited by rapamycin, a naturally occurring antifungal compound produced by bacteria and discovered on Easter Island or in the local vernacular, Rapa Nui (rapamycin's namesake). Recently, rapamycin was shown to extend life span for mice, even when administered late in life, suggesting that inhibiting the mammalian TOR pathway may improve health span for people.

Identity Crisis When Telomeres Left Unprotected

Wu, Y., Zakian, V. A. — Sun, 04 Oct 2009 23:53:10 PDT

Loss of shelterin components TRF2 or POT1a–TPP1 complex from the chromosome end triggers DNA damage response (DDR) and aberrant DNA repair events. In a recent Nature paper, Chang and colleagues reported that the DNA repair protein Mre11 contributes to multiple events at the uncapped telomere, including ataxia telangiectasia-mutated (ATM)-dependent signaling, processing of the telomeric G-tail and homologous recombination (HR).

Home Improvements: How the Malaria Parasite Makes the Red Blood Cell Home Sweet Home

Starnes, G. L., Waters, A. P. — Sun, 04 Oct 2009 23:53:09 PDT

A recent study published in Nature by de Koning-Ward et al. provides further insights into the way in which the lethal malaria parasite, Plasmodium falciparum, remodels the host red blood cell during the pathogenic blood stage of development.

A Little 'Help' from IL-21 During Persistent Viral Infection

McGavern, D. B. — Thu, 01 Oct 2009 03:42:23 PDT

Anti-viral CD4⁺ T cells are required to orchestrate and sustain the activities of the adaptive immune system during a persistent viral infection. Three recent studies suggest that CD4⁺ T cells accomplish this in part through the release of IL-21.

An Expanding Job Description for Bcl6

Bi, E., Ye, B. H. — Wed, 30 Sep 2009 23:50:27 PDT

B cell lymphoma/leukemia gene 6 (Bcl6) is well known as a master regulator of germinal center (GC) B cell differentiation. Now, three new publications demonstrate that Bcl6 also plays a second role in GC response, in that it is both required and sufficient to drive the differentiation of T follicular helper cells.

Paracrine Unpaired Signaling through the JAK/STAT Pathway Controls Self-renewal and Lineage Differentiation of Drosophila Intestinal Stem Cells

Lin, G., Xu, N., Xi, R. — Wed, 30 Sep 2009 23:50:26 PDT

Drosophila and mammalian intestinal stem cells (ISCs) share similarities in their regulatory mechanisms, with both requiring Wingless (Wg)/Wnt signaling for their self-renewal, although additional regulatory mechanisms are largely unknown. Here we report the identification of Unpaired as another paracrine signal from the muscular niche, which activates a canonical JAK/STAT signaling cascade in Drosophila ISCs to regulate ISC self-renewal and differentiation. We show that compromised JAK signaling causes ISC quiescence and loss, whereas signaling overactivation produces extra ISC-like and progenitor cells. Simultaneous disruption or activation of both JAK and Wg signaling in ISCs results in a stronger ISC loss or a greater expansion of ISC-like cells, respectively, than by altering either pathway alone, indicating that the two pathways function in parallel. Furthermore, we show that loss of JAK signaling causes blockage of enteroblast differentiation and reduced JAK signaling preferentially affects enteroendocrine (ee) cell differentiation. Conversely, JAK overactivation produces extra differentiated cells, especially ee cells. Together with the functional analysis with Notch (N), we suggest two separate roles of JAK/STAT signaling in Drosophila ISC lineages: it functions upstream of N, in parallel and cooperatively with Wg signaling to control ISC self-renewal; it also antagonizes with N activity to control the binary fate choice of intestinal progenitor cells.

Embryonic vs. Adult Myogenesis: Challenging the 'Regeneration Recapitulates Development' Paradigm

Wang, J., Conboy, I. — Wed, 30 Sep 2009 23:50:24 PDT

A popular theory in the stem cell field is that ‘regeneration recapitulates development’, or that adult stem cells function similarly to embryonic ones. In a recent Nature article, Lepper et al. questioned this approach, highlighting the differences in requirements for Pax7 during myogenesis for embryonic, juvenile and adult muscle.

TGF-{beta} and 'Adaptive' Foxp3+ Regulatory T cells

Chen, W., Konkel, J. E. — Fri, 31 Jul 2009 07:25:27 PDT

In naïve T cells transforming growth factor-beta (TGF-β) induces Foxp3, a transcription factor essential for programming and developing T regulatory cells (Treg cells). This finding reveals a physiological factor which can turn on the Foxp3 gene and establishes an experimental approach to induce antigen-specific Treg cells as a potential therapy for human diseases. While this role for TGF-β is well confirmed, several critical questions remain largely unanswered and await further investigation. In this regard, it is imperative to understand the molecular pathways by which TGF-β signaling initiates and regulates Foxp3 expression. It is also important to elucidate which factors and/or cytokines influence the TGF-β-mediated conversion of naïve T cells and how to create an immunologically regulatory milieu to facilitate Treg cell generation in vivo. In this short article, we will highlight the key findings and recent progress in the field, discuss the molecular mechanisms underlying the TGF-β-mediated induction of Foxp3, and attempt to outline the challenges ahead.