Search

Here, plant HAM proteins are shown to physically interact with the transcription factor WUSCHEL and the related WOX proteins, with this interaction driving downstream transcriptional programs and determining the activities of stem cells. Regulation of plant stem cell function Postembryonic development of above-ground tissues and of roots of plants depends on stem cells in the shoot and root apical meristems, respectively. The transcription factor WUSCHEL (WUS) and the related WOX proteins are known to be involved in the specification and maintenance of stem cells within all meristems throughout the plant kingdom. The HAIRY MERISTEM (HAM) family of transcription regulators is known to contribute to shoot stem cell function in certain plant species. The present paper shows that WOX and HAM family proteins act together to control the production of all types of stem cells in diverse niches in Arabidopsis, and that WUS and HAM share some common targets in vivo. Differences in the combined expression patterns of WOX and HAM family members appear to determine the formation of diverse stem cell niche locations. These findings demonstrate how co-operative transcriptional regulators drive common regulatory pathways and point to mechanisms underlying the evolution of stem cell regulation in plants. Plant stem cells in the shoot apical meristem (SAM) and root apical meristem are necessary for postembryonic development of aboveground tissues and roots, respectively, while secondary vascular stem cells sustain vascular development.sup.1,2,3,4. WUSCHEL (WUS), a homeodomain transcription factor expressed in the rib meristem of the Arabidopsis SAM, is a key regulatory factor controlling SAM stem cell populations.sup.5,6, and is thought to establish the shoot stem cell niche through a feedback circuit involving the CLAVATA3 (CLV3) peptide signalling pathway.sup.7. WUSCHEL-RELATED HOMEOBOX 5 (WOX5), which is specifically expressed in the root quiescent centre, defines quiescent centre identity and functions interchangeably with WUS in the control of shoot and root stem cell niches.sup.8. WOX4, expressed in Arabidopsis procambial cells, defines the vascular stem cell niche.sup.9,10,11. WUS/WOX family proteins are evolutionarily and functionally conserved throughout the plant kingdom.sup.12 and emerge as key actors in the specification and maintenance of stem cells within all meristems.sup.13. However, the nature of the genetic regime in stem cell niches that centre on WOX gene function has been elusive, and molecular links underlying conserved WUS/WOX function in stem cell niches remain unknown. Here we demonstrate that the Arabidopsis HAIRY MERISTEM (HAM) family of transcription regulators act as conserved interacting cofactors with WUS/WOX proteins. HAM and WUS share common targets in vivo and their physical interaction is important in driving downstream transcriptional programs and in promoting shoot stem cell proliferation. Differences in the overlapping expression patterns of WOX and HAM family members underlie the formation of diverse stem cell niche locations, and the HAM family is essential for all of these stem cell niches. These findings establish a new framework for the control of stem cell production during plant development., Author(s): Yun Zhou [sup.1] , Xing Liu [sup.1] , Eric M. Engstrom [sup.2] [sup.6] , Zachary L. Nimchuk [sup.1] [sup.3] [sup.6] , Jose L. Pruneda-Paz [sup.4] , Paul T. Tarr [...]

High-fat feeding that induces hyperlipidemia and antherogenesis, stimulates the expression of both PGC-1 beta and sterol responsive element binding protein (SREBP)1c and 1a in liver is described. Unlike SREBP itself, PGC-1beta reduces fat accumulation in the liver while greatly increasing circulating triglycerides and cholesterol in VLDL particles.

Skeletal muscle adapts to chronic physical activity by inducing mitochondrial biogenesis and switching proportions of muscle fibers from type II to type I. Several major factors involved in this process have been identified, such as the calcium/calmodulin-dependent protein kinase IV (CaMKIV), calcineurin A (CNA), and the transcriptional component peroxisome proliferator-activated receptor [gamma] coactivator 1[alpha] (PGC-1[alpha]). Transgenic expression of PGC-1[alpha] recently has been shown to dramatically increase the content of type I muscle fibers in skeletal muscle, but the relationship between PGC-1[alpha] expression and the key components in calcium signaling is not clear. In this report, we show that the PGC-1[alpha] promoter is regulated by both CaMKIV and CnA activity. CaMKIV activates PGC-1[alpha] largely through the binding of cAMP response element-binding protein to the PGC-1[alpha] promoter. Moreover, we show that a positive feedback loop exists between PGC-1[alpha] and members of the myocyte enhancer factor 2 (MEF2) family of transcription factors. MEF2s bind to the PGC-1[alpha] promoter and activate it, predominantly when coactivated by PGC-1[alpha]. MEF2 activity is stimulated further by CnA signaling. These findings imply a unified pathway, integrating key regulators of calcium signaling with the transcriptional switch PGC-1[alpha]. Furthermore, these data suggest an autofeedback loop whereby the calcium-signaling pathway may result in a stable induction of PGC-1[alpha], contributing to the relatively stable nature of muscle fiber-type determination.

Author(s): Jiandie Lin [1]; Hai Wu [2]; Paul T. Tarr [1]; Chen-Yu Zhang [3]; Zhidan Wu [1]; Olivier Boss [3]; Laura F. Michael [1]; Pere Puigserver [1]; Eiji Isotani [4]; [...]

PGC-alpha is a coactivator of nuclear receptors and other transcription factors that regulates several metabolic processes, including mitochondrial biogenesis and respiration, hepatic gluconeogenesis, and muscle fiber-type switching. The central role for PGC-1 alpha in the control of energy metabolism is illustrated.

The Arabidopsis thaliana leucine-rich repeat receptor kinase FLAGELLIN SENSING2 (FLS2) is required for the recognition of bacterial flagellin in innate immunity. Recently, FLS2 was proposed to act as a multispecific receptor recognizing unrelated exogenous and endogenous peptide ligands, including CLAVATA3 (CLV3), a key regulator of shoot meristem stem cell production. Here, we report experimental evidence demonstrating that FLS2 does not recognize CLV3 and that the shoot apical meristem is immune to bacteria independently of CLV3 perception. [ABSTRACT FROM AUTHOR]

Sequence comparisons, biochemical experiments, and studies with mutants in transgenic plants show that the Arabidopsis protein CORYNE, currently thought to be a kinase that acts as part of a receptor kinase complex, is likely to be a pseudokinase and not a kinase. [ABSTRACT FROM AUTHOR]

Peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) is a transcriptional coactivator that regulates multiple aspects of cellular energy metabolism, including mitochondrial biogenesis, hepatic gluconeogenesis, and β-oxidation of fatty acids. PGC-1α mRNA levels are increased in both type-1 and type-2 diabetes and may contribute to elevated hepatic glucose production in diabetic states. We have recently described PGC-1β, a novel transcriptional coactivator that is a homolog of PGC-1α. Although PGC-1β shares significant sequence similarity and tissue distribution with PGC-1α, the biological activities of PGC-1β in the regulation of cellular metabolism is unknown. In this study, we used an adenoviral-mediated expression system to study the function of PGC-1β both in cultured hepatocytes and in the liver of rats. PGC-1β, like PGC-1α, potently induces the expression of an array of mitochondrial genes involved in oxidative metabolism. However, in contrast to PGC-1α, PGC-1β poorly activates the expression of gluconeogenic genes in hepatocytes or liver in vivo, illustrating that these two coactivators play distinct roles in hepatic glucose metabolism. The reduced ability of PGC-1β to induce gluconeogenic genes is due, at least in part, to its inability to physically associate with and coactivate hepatic nuclear receptor 4α (HNF4α) and forkhead transcription factor O1 (FOXO1), two critical transcription factors that mediate the activation of gluconeogenic gene expression by PGC-1α. These data illustrate that PGC-1β and PGC-1α have distinct arrays of activities in hepatic energy metabolism. [ABSTRACT FROM AUTHOR]

Quantitative studies in plant developmental biology require monitoring and measuring the changes in cells and tissues as growth gives rise to intricate patterns. The success of these studies has been amplified by the combined strengths of two complementary techniques, namely live imaging and computational image analysis. Live imaging records time-lapse images showing the spatial-temporal progress of tissue growth with cells dividing and changing shape under controlled laboratory experiments. Image processing and analysis make sense of these data by providing computational ways to extract and interpret quantitative developmental information present in the acquired images. Manual labeling and qualitative interpretation of images are limited as they don't scale well to large data sets and cannot provide field measurements to feed into mathematical and computational models of growth and patterning. Computational analysis, when it can be made sufficiently accurate, is more efficient, complete, repeatable, and less biased. In this chapter, we present some guidelines for the acquisition and processing of images of sepals and the shoot apical meristem of Arabidopsis thaliana to serve as a basis for modeling. We discuss fluorescent markers and imaging using confocal laser scanning microscopy as well as present protocols for doing time-lapse live imaging and static imaging of living tissue. Image segmentation and tracking are discussed. Algorithms are presented and demonstrated together with low-level image processing methods that have proven to be essential in the detection of cell contours. We illustrate the application of these procedures in investigations aiming to unravel the mechanical and biochemical signaling mechanisms responsible for the coordinated growth and patterning in plants., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Peroxisome proliferator-activated receptor gamma coactivator (PGC)-1alpha is a coactivator of nuclear receptors and other transcription factors that regulates several components of energy metabolism, particularly certain aspects of adaptive thermogenesis in brown fat and skeletal muscle, hepatic gluconeogenesis, and fiber type switching in skeletal muscle. PGC-1alpha has been shown to induce mitochondrial biogenesis when expressed in muscle cells, and preliminary analysis has suggested that this molecule may specifically increase the fraction of uncoupled versus coupled respiration. In this paper, we have performed detailed bioenergetic analyses of the function of PGC-1alpha and its homolog PGC-1beta in muscle cells by monitoring simultaneously oxygen consumption and membrane potential. Cells expressing PGC-1alpha or PGC-1beta display higher proton leak rates at any given membrane potential than control cells. However, cells expressing PGC-1alpha have a higher proportion of their mitochondrial respiration linked to proton leak than cells expressing PGC-1beta. Although these two proteins cause a similar increase in the expression of many mitochondrial genes, PGC-1beta preferentially induces certain genes involved in the removal of reactive oxygen species, recently recognized as activators of uncoupling proteins. Together, these data indicate that PGC-1alpha and PGC-1beta profoundly alter mitochondrial metabolism and suggest that these proteins are likely to play different physiological functions.