HDAC4 regulates skeletal muscle regeneration via soluble factors

Skeletal muscle possesses a high ability to regenerate after an insult or in pathological conditions, relying on satellite cells, the skeletal muscle stem cells. Satellite cell behavior is tightly regulated by the surrounding microenvironment, which provides multiple signals derived from local cells and systemic factors. Among epigenetic mechanisms, histone deacetylation has been proved to affect muscle regeneration. Indeed, pan-histone deacetylase inhibitors were found to improve muscle regeneration, while deletion of histone deacetylase 4 (HDAC4) in satellite cells inhibits their proliferation and differentiation, leading to compromised muscle regeneration. In this study, we delineated the HDAC4 function in adult skeletal muscle, following injury, by using a tissue-specific null mouse line. HDAC4 resulted crucial for skeletal muscle regeneration by mediating soluble factors that influence muscle-derived cell proliferation and differentiation. These findings add new biological functions to HDAC4 in skeletal muscle that need considering when administering histone deacetylase inhibitors

Updating the Merger Guidelines: Comments

These comments (originally submitted to the DOJ and FTC in November 2009) make a number of comments relevant to revising the Merger Guidelines. The comments focus on the use of the GUPPI (gross upward pricing pressure index) in unilateral effects analysis. They also comment on the deterrence and incipiency standard, exclusionary effects of horizontal mergers and market definition when there are multi-product firms or pre-merger coordination, among other issues

Of faeces and sweat. How much a mouse is willing to run: having a hard time measuring spontaneous physical activity in different mouse sub-strains

Physical activity has multiple beneficial effects in the physiology and pathology of the organism. In particular, we and other groups have shown that running counteracts cancer cachexia in both humans and rodents. The latter are prone to exercise in wheel-equipped cages even at advanced stages of cachexia. However, when we wanted to replicate the experimental model routinely used at the University of Rome in a different laboratory (i.e. at Paris 6 University), we had to struggle with puzzling results due to unpredicted mouse behavior. Here we report the experience and offer the explanation underlying these apparently irreproducible results. The original data are currently used for teaching purposes in undergraduate student classes of biological sciences

New insights into the epigenetic control of satellite cells

Epigenetics finely tunes gene expression at a functional level without modifying the DNA sequence, thereby contributing to the complexity of genomic regulation. Satellite cells (SCs) are adult muscle stem cells that are important for skeletal post-natal muscle growth, homeostasis and repair. The understanding of the epigenome of SCs at different stages and of the multiple layers of the post-transcriptional regulation of gene expression is constantly expanding. Dynamic interactions between different epigenetic mechanisms regulate the appropriate timing of muscle-specific gene expression and influence the lineage fate of SCs. In this review, we report and discuss the recent literature about the epigenetic control of SCs during the myogenic process from activation to proliferation and from their commitment to a muscle cell fate to their differentiation and fusion to myotubes. We describe how the coordinated activities of the histone methyltransferase families Polycomb group (PcG), which represses the expression of developmentally regulated genes, and Trithorax group, which antagonizes the repressive activity of the PcG, regulate myogenesis by restricting gene expression in a time-dependent manner during each step of the process. We discuss how histone acetylation and deacetylation occurs in specific loci throughout SC differentiation to enable the time-dependent transcription of specific genes. Moreover, we describe the multiple roles of microRNA, an additional epigenetic mechanism, in regulating gene expression in SCs, by repressing or enhancing gene transcription or translation during each step of myogenesis. The importance of these epigenetic pathways in modulating SC activation and differentiation renders them as promising targets for disease interventions. Understanding the most recent findings regarding the epigenetic mechanisms that regulate SC behavior is useful from the perspective of pharmacological manipulation for improving muscle regeneration and for promoting muscle homeostasis under pathological conditions

Market Definition

We explain the “hypothetical monopolist test” that has become the standard methodology for identifying relevant antitrust markets in merger cases, and discuss two approaches to implementing the test. We then focus on the implementation of the test when firms offer multiple products or services, either inside or outside the candidate market, and discuss the “hypothetical cartel test” introduced in the 2010 U.S. Merger Guidelines

Regulation of skeletal muscle development and homeostasis by gene imprinting, histone acetylation and microRNA

Epigenetics is defined as heritable information other that the DNA sequence itself. The concept implies that the regulation of gene expression is highly complex and epigenetics can control from fine tuning to permanent gene activation/deactivation. Skeletal muscle is the main tissue for locomotion and energy metabolism in the body, and represent at least 40% of the body mass. Body mass and function vary according to age but also quickly adapt to physiological as well as pathological cues. Besides transcriptional mechanisms that control muscle differentiation, postnatal growth and remodeling, there are numerous epigenetic mechanisms of regulation that modulate muscle gene expression. In this review, we describe and discuss only some of the mechanisms of epigenetic regulation - such as DNA methylation, histone modifications, and microRNAs - that have been characterized in detail and that we believe are crucial for skeletal muscle development and disease

Coordinated actions of microRNAs with other epigenetic factors regulate skeletal muscle development and adaptation

Epigenetics plays a pivotal role in regulating gene expression in development, in response to cellular stress or in disease states, in virtually all cell types. MicroRNAs (miRNAs) are short, non-coding RNA molecules that mediate RNA silencing and regulate gene expression. miRNAs were discovered in 1993 and have been extensively studied ever since. They can be expressed in a tissue-specific manner and play a crucial role in tissue development and many biological processes. miRNAs are responsible for changes in the cell epigenome because of their ability to modulate gene expression post-transcriptionally. Recently, numerous studies have shown that miRNAs and other epigenetic factors can regulate each other or cooperate in regulating several biological processes. On the one hand, the expression of some miRNAs is silenced by DNA methylation, and histone modifications have been demonstrated to modulate miRNA expression in many cell types or disease states. On the other hand, miRNAs can directly target epigenetic factors, such as DNA methyltransferases or histone deacetylases, thus regulating chromatin structure. Moreover, several studies have reported coordinated actions between miRNAs and other epigenetic mechanisms to reinforce the regulation of gene expression. This paper reviews multiple interactions between miRNAs and epigenetic factors in skeletal muscle development and in response to stimuli or disease

Magnetic resonance force microscopy : interaction forces and channels of energy dissipation

Today, smaller and smaller electron and nuclear magnetic resonance structures are extensively studied both from an applied and from a fundamental point of view. The powerful tool of magnetic resonance imaging (MRI) has demonstrated that it is possible to visualize subsurface three dimensional structures with micrometer resolution [1] containing 1012 nuclear spins; nuclear magnetic resonance (NMR) spectroscopy has the capacity to determine the three dimensional structure of biological macromolecules [2]. Owing to the larger gyromagnetic ratio of electrons as compared to paramagnetic nuclei, electron spin resonance (ESR) has pushed detection sensitivity to 107 spins [3]. Finally, a single electron spin [4] has been detected by magnetic resonance force microscopy (MRFM), employing a device which combines two sensing technologies, namely magnetic resonance imaging (MRI) and atomic force microscopy (AFM). The ultimate goal of MRFM is to map the interior of a material sample, such as a complicated semiconductor structure or a bio-molecule, at atomic scale resolution. The idea of introducing MRFM to improve the detection sensitivity down to a single spin and thus to resolve atoms of proteins [5],[6] was originally proposed in 1992. Ten years later, Rugar and co-workers reported the detection of a single electron spin resonance in a silica substrate with paramagnetic defects, using a magnetic resonance force microscope [4] with a lateral resolution of 25 nm in one dimension. To achieve this single spin detection, the magnetic resonance force microscopy uses a soft cantilever with a tiny hard magnetic tip material. The inhomogeneity field Binhom generated from the magnetic tip is superimposed with the homogenous magnetic field B0 which polarizes the sample. For a radio frequency field the resonance condition is fulfilled in the region where !1 = (B0 + Bgrad) and where is the gyromagnetic ratio of electron or proton. Consequently, the next foreseeable step is to detect a single nuclear spin. In fact, the correspondence between ESR and NMR is very close, and much of the basic theory of ESR is directly applicable to NMR. ESR requires an unpaired electron whereas NMR requires an unpaired nuclear spin for detection. Furthermore, an external static magnetic field is necessary in both ESR and NMR detection. The major difference between the two techniques is due to the gyromagnetic ratio of the proton and electron. ESR entails the higher electron gyromagnetic ratio, as compared to the nuclear gyromagnetic ratio involved in NMR and the sensitivity of EPR is correspondingly higher (approximately a factor of 1000). The force generated by a single spin is in the attonewton range. Thus, non commercial, soft single crystalline silicon cantilevers with a high quality factor and minimized spring constants have to be used for detecting a single spin. Measurements are performed at liquid helium temperature where thermal noise is reduced by a factor of 10. The UHV condition makes for a very stable environment reducing the oxidation of the sample and of the cantilever. In our low temperature force microscope force sensitivities on the order of 10−18 N/pHz at 10 K are obtained without any external static field [7]. A force sensitivity in the order of 9x10−18 N/pHz should be reached at 4 K in a static magnetic field of 100 mT. In this work we design, build and assemble the entire UHV machine working at a pressure of <10−10 mbar and at helium boiling temperature starting from the existing microscope and the Janis cryostat. This work took about one year producing hundreds of schemes and designs. The entire cryogenic machine plan is detailed in the appendix. For detailed subsystem schemes please refer to the scheme library in the appendices. The extreme high sensitivity of 10−18 N/pHz that the magnetic force resonance microscope should reach, requires the study of interaction phenomena. The small spring constant for high force sensitivity makes it necessary to have the cantilever perpendicular to the sample surface. Otherwise, the cantilever will stick electrostatically to the sample surface. This vertical configuration introduces new design parameters involving the cantilever’s approach to the sample. In fact the cantilever is subject not only on the lateral force gradient but also to a vertical force. The vertical attractive force as a uniform force will cause an increase in the frequency similar to the uniform gravitational force that causes a pendulum to have a frequency that is proportional to gravity. The tip-sample interaction dissipation is then measured by the Q factor change as a function of the distance. The dissipation is caused mainly by the electrostatic charge fluctuation. The fluctuation of charge stored on a capacitance C induces the noise denoted as ”KTC”. The noise of the fluctuation charge is on the order of observed charge fluctuations of single-electron transistors. This shows a probably common origin of the charge fluctuation. A severe loss in force sensitivity and a frequency shift are observed while exposing the cantilever with a magnetic tip to a homogenous magnetic field. The micrometer sized magnetic particles generate a magnetic field of 500 Gauss and magnetic field gradients (dB/dz>> 1x105 T/m). To minimize the damping losses of the cantilevers with ferromagnetic particles various magnetic materials (e.g. Sm2Co17, SmCo5, Nd2Fe14B, and Pr2Fe14B) with different grain materials and domain sizes are investigated. The lowest magnetic dissipation is observed with SmCo5 tips having a higher anisotropy constant. A correlation between frequency of oscillation and magnetic field hysteresis is then measured. A detection sensitivity in the order of 10−18N/pHz is reached at 100 mT. This sensitivity should be enough for measuring less than 100 electron spins. Finally, a home-built spectrometer is compared with a home-built magnetic resonance force microscope with the sample mounted on the cantilever. At room temperature and at 50 mT the magnetic resonance force microscope has a sensitivity improvement of a factor of more than 100000. This suggests the huge potential of this instrument for biological and chemical sample analysis. This work is part of ultimate limits of measurement of module IX of the National Center of Competence in Research in Nanoscience (NCCR). The NCCR is the national Swiss research projects in nano technologies with the leading house in Basel. The main goal of this submodule is to ultimately perform single spin experiments at low temperature and in ultra high vacuum (UHV). Achieving this goal requires mechanical force sensors to be improved and all relevant forces to be understood. The channels of energy dissipation should be determined in order to improve the detection sensitivity

Equipping Citylife Adults to Navigate the Faith Formation Stages of Doubt and Spiritual Darkness

CityLife Church is an independent, Pentecostal, Mega Church, gathering in three locations across Melbourne, Australia. With a large Asian population, congregants are generally financially stable, well-educated and success-oriented. Fundamental Pentecostal teachings have created an expectation where supernatural engagement with the Holy Spirit is an anticipated outcome of faith in Christ. This concentration on the upbeat, outward expression of one’s faith often leaves the community unprepared and ill equipped to navigate the inevitable faith formation stages of doubt and spiritual darkness. This doctoral project will equip adult members of CityLife Church, who traditionally struggle to acknowledge these stages, identify, understand, and navigate them through the development of an integrated strategy of pulpit teaching and small group engagement. Proposing an integrated strategy of pulpit teaching and small group engagement, CityLife adults will understand that Christ-like maturity is a lifelong process, and that these challenging stages are vital to the process of transformation. The pulpit teaching and parallel small-group studies will enable believers to identify and normalize their own faith formation stage, and that of others within the community, promoting authentic relationships. Part One of this paper will examine the community context of CityLife Church. Part Two will engage the biblical and theological foundations for this project. Key theological texts will be outlined, together with Scriptures supporting the necessity of stages of doubt and spiritual darkness in the maturing process. Part Three will present a ministry plan to address the need for CityLife adults to understand and navigate the challenging faith formation stages. Specific goals relating to the desired outcomes will be discussed, together with a project timeline, which will provide a clear framework for the strategy content. Content Reader: Kurt Fredrickson, Ph

A benchmark study on mantle convection in a 3-D spherical shell using CitcomS

As high-performance computing facilities and sophisticated modeling software become available, modeling mantle convection in a three-dimensional (3-D) spherical shell geometry with realistic physical parameters and processes becomes increasingly feasible. However, there is still a lack of comprehensive benchmark studies for 3-D spherical mantle convection. Here we present benchmark and test calculations using a finite element code CitcomS for 3-D spherical convection. Two classes of model calculations are presented: the Stokes' flow and thermal and thermochemical convection. For Stokes' flow, response functions of characteristic flow velocity, topography, and geoid at the surface and core-mantle boundary (CMB) at different spherical harmonic degrees are computed using CitcomS and are compared with those from analytic solutions using a propagator matrix method. For thermal and thermochemical convection, 24 cases are computed with different model parameters including Rayleigh number (7 × 10^3 or 10^5) and viscosity contrast due to temperature dependence (1 to 10^7). For each case, time-averaged quantities at the steady state are computed, including surface and CMB Nussult numbers, RMS velocity, averaged temperature, and maximum and minimum flow velocity, and temperature at the midmantle depth and their standard deviations. For thermochemical convection cases, in addition to outputs for thermal convection, we also quantified entrainment of an initially dense component of the convection and the relative errors in conserving its volume. For nine thermal convection cases that have small viscosity variations and where previously published results were available, we find that the CitcomS results are mostly consistent with these previously published with less than 1% relative differences in globally averaged quantities including Nussult numbers and RMS velocities. For other 15 cases with either strongly temperature-dependent viscosity or thermochemical convection, no previous calculations are available for comparison, but these 15 test calculations from CitcomS are useful for future code developments and comparisons. We also presented results for parallel efficiency for CitcomS, showing that the code achieves 57% efficiency with 3072 cores on Texas Advanced Computing Center's parallel supercomputer Ranger