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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2010.01.006 Byline: Kenneth Day (a), Gabi Shefer (a)(b), Andrew Shearer (a), Zipora Yablonka-Reuveni (a) Keywords: Stem cells; Satellite cells; Reserve cells; Aging; Myogenesis; Skeletal muscle; Nestin-GFP; Myf5.sup.nLacZ/+; MLC3F-nLacZ, Myostatin; Pax7, [alpha]7 integrin, Myf5 Abstract: Satellite cells are myogenic progenitors that reside on the myofiber surface and support skeletal muscle repair. We used mice in which satellite cells were detected by GFP expression driven by nestin gene regulatory elements to define age-related changes in both numbers of satellite cells that occupy hindlimb myofibers and their individual performance. We demonstrate a reduction in satellite cells per myofiber with age that is more prominent in females compared to males. Satellite cell loss also persists with age in myostatin-null mice regardless of increased muscle mass. Immunofluorescent analysis of isolated myofibers from nestin-GFP/Myf5.sup.nLacZ/+ mice reveals a decline with age in the number of satellite cells that express detectable levels of [beta]gal. Nestin-GFP expression typically diminishes in primary cultures of satellite cells as myogenic progeny proliferate and differentiate, but GFP subsequently reappears in the Pax7.sup.+ reserve population. Clonal analysis of sorted GFP.sup.+ satellite cells from hindlimb muscles shows heterogeneity in the extent of cell density and myotube formation among colonies. Reserve cells emerge primarily within high-density colonies, and the number of clones that produce reserve cells is reduced with age. Thus, satellite cell depletion with age could be attributed to a reduced capacity to generate a reserve population. Author Affiliation: (a) Department of Biological Structure, Box 357420, Warren B. Magneson Health Sciences Building, 1959 NE Pacific Street, University of Washington School of Medicine, Seattle, WA 98195, USA (b) Department of Cell and Development Biology, Sackler Faculty of Medicine, Tel-Aviv University, Tel-Aviv 69978, Israel Article History: Received 28 August 2009; Revised 6 January 2010; Accepted 7 January 2010

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2007.08.056 Byline: Irina Kirillova (a), Emanuela Gussoni (b), David J. Goldhamer (c), Zipora Yablonka-Reuveni (a) Keywords: Retina; Vasculature; Endothelial cells; Pericytes; Skeletal muscle; Myogenesis; Satellite cells; Sca1; MyoD; Myf5 Abstract: Satellite cells are recognized as the main source for myoblasts in postnatal muscle. The possible participation of other cell types in myofiber maintenance remains a subject of debate. Here, we investigated the potential of vascular preparations from mouse retina to undergo myogenesis when cultured alone or with differentiated primary myogenic cultures. The choice of retina, an organ richly supplied with capillary network and anatomically separated from skeletal muscles, ensures that the vasculature preparation is devoid of satellite cells. We demonstrate that retina-derived cells spontaneously fuse with preexisting myotubes and contribute additional myonuclei, some of which initiate expression of muscle-specific genes after fusion. Myogenic differentiation of retinal cells prior to their fusion with preexisting myotubes was not detected. Although originating from vasculature preparations, nuclei undergoing myogenic reprogramming were contributed by cells that were neither endothelial nor blood borne. Our results suggest smooth muscle/pericytes as the possible source, and that myogenic reprogramming depends on the muscle specific transcription factor MyoD. Our studies provide insights into a novel avenue for myofiber maintenance, relying on nuclei of non-myogenic origin that undergo fusion and subsequent myogenic conversion within host myofibers. This process may support ongoing myofiber maintenance throughout life. Author Affiliation: (a) Department of Biological Structure, University of Washington School of Medicine, Magnuson Health Sciences Center, Box 357420, Room I-146, 1959 NE Pacific Street, Seattle, WA 98195, USA (b) Division of Genetics, Children's Hospital Boston, Boston, MA 02115, USA (c) Department of Molecular and Cell Biology, Center for Regenerative Biology, University of Connecticut, Storrs, CT 06269, USA Article History: Received 23 June 2007; Revised 3 August 2007; Accepted 28 August 2007

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2006.12.026 Byline: Kenneth Day (a), Gabi Shefer (a), Joshua B. Richardson (a), Grigori Enikolopov (c), Zipora Yablonka-Reuveni (a)(b) Keywords: Satellite cells; Self-renewal; Stem cells; Endothelial cells; Nestin; Desmin; Myf5; Pax3; Pax7; Sca1; CD31; GFP; Sca1-GFP; Nestin-GFP Abstract: Repair of adult skeletal muscle depends on satellite cells, quiescent myogenic stem cells located beneath the myofiber basal lamina. Satellite cell numbers and performance decline with age and disease, yet the intrinsic molecular changes accompanying these conditions are unknown. We identified expression of GFP driven by regulatory elements of the nestin (NES) gene within mouse satellite cells, which permitted characterization of these cells in their niche. Sorted NES-GFP.sup.+ cells exclusively acquired a myogenic fate, even when supplemented with media supporting non-myogenic development. Mutual and unique gene expression by NES-GFP.sup.+ cells from hindlimb and diaphragm muscles demonstrated intra- and inter-muscular heterogeneity of satellite cells. NES-GFP expression declined following satellite cell activation and was reacquired in late stage myogenic cultures by non-proliferating Pax7.sup.+ progeny. The dynamics of this expression pattern reflect the cycle of satellite cell self-renewal. The NES-GFP model reveals unique transcriptional activity within quiescent satellite cells and permits novel insight into the heterogeneity of their molecular signatures. Author Affiliation: (a) Department of Biological Structure, University of Washington School of Medicine, Seattle, WA 98195, USA (b) Institute for Stem Cell and Regenerative Medicine, University of Washington School of Medicine, Seattle, WA 98195, USA (c) Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724, USA Article History: Received 25 August 2006; Revised 7 November 2006; Accepted 12 December 2006

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2006.02.022 Byline: Gabi Shefer, Daniel P. Van de Mark, Joshua B. Richardson, Zipora Yablonka-Reuveni Keywords: Myogenesis; Satellite cell; Cell renewal; Stem cell; Myofiber; Myoblast; Pax7; MyoD; FGF; Aging; Sarcopenia; Mouse Abstract: The deteriorating in vivo environment is thought to play a major role in reduced stem cell function with age. The capacity of stem cells to support tissue maintenance depends not only on their response to cues from the surrounding niche, but also on their abundance. Here, we investigate satellite cell (myogenic stem cell) pool size and its potential to participate in muscle maintenance through old age. The numbers and performance of mouse satellite cells have been analyzed using molecular markers that exclusively characterize quiescent satellite cells and their progeny as they transit through proliferation, differentiation and generation of reserve cells. The study establishes that abundance of resident satellite cells declines with age in myofibers from both fast- and slow-twitch muscles. Nevertheless, the inherent myogenic potential of satellite cells does not diminish with age. Furthermore, the aging satellite cell niche retains the capacity to support effective myogenesis upon enrichment of the mitogenic milieu with FGF. Altogether, satellite cell abundance, but not myogenic potential, deteriorates with age. This study suggests that the population of satellite cells that participate in myofiber maintenance during routine muscle utilization is not fully replenished throughout life. Author Affiliation: Department of Biological Structure, School of Medicine, University of Washington, Magnuson Health Sciences Center, Room G514, Box 357420, Seattle, WA 98195, USA Article History: Received 4 December 2005; Revised 13 February 2006; Accepted 15 February 2006

Our previous studies demonstrated that illumination of chicken embryos with monochromatic green light results in enhanced body and muscle weight at later posthatch stages. In the present study, we investigated the cellular and molecular basis of this phenomenon. First, we showed that on day 6 posthatch, myofibers were more uniform in the in ovo illuminated group than in the control group incubated in the dark, with respect to the number of myofibers displaying diameter values within the range of the mean value. Second, we tested the hypothesis that in ovo illumination causes an increase in the number of myoblasts; this in turn can promote posthatch muscle growth. Indeed, a significant increase in the number of skeletal muscle cells isolated from pectoralis muscle was observed in the in ovo illuminated group on days 1 and 3 posthatch relative to the control group. This increased cell number was accompanied by higher expression levels of Pax7 and myogenin proteins on posthatch days 1 and 3, respectively. A parallel analysis of proliferating cells in the intact muscle further demonstrated a significant increase in the number of cells positive for proliferating cell nuclear antigen in muscle from the in ovo illuminated group. Third, we demonstrated that the transition from fetal- to adult-type myoblasts, normally occurring in late stages of chicken embryogenesis, is initiated earlier in embryos subjected to in ovo green-light illumination. We suggest that the stimulatory effect of in ovo illumination on posthatch muscle growth is the result of enhanced proliferation and differentiation of adult myoblasts and myofiber synchronization. satellite cells; Pax7; myogenin; myoblasts; chicken

The proper patterning of somites to give rise to sclerotome, dermomyotome, and myotome involves the coordination of many different cellular processes, including lineage specification, cell proliferation, cell death, and differentiation, by intercellular signals. One such family of secreted signaling proteins known to influence somite patterning is the Wnt family. Although the participation of Wnt-3a in the patterning of dorsal structures in the somite is well established, no clear consensus has emerged about the cellular processes that are governed by Wnt-3a in the somite. The recent demonstration that Wnt-3a has a proliferative role in the neural tube [Development 129 (2002) 2087] suggested that Wnt-3a might also act to regulate proliferation in somites. To test this hypothesis, we first analyzed the effects of Wnt-3a on segmental plate and somite explants (from Hamburger and Hamilton stage 10 chick embryos) grown in culture. These studies indicate that Wnt-3a is capable of maintaining and/or inducing expression of both Pax-3 and Pax-7, transcription factors that have been implicated in proliferation. To directly test for a role in proliferation, explants were immunostained with antibodies against phospho-histone H3. Explants treated with Wnt-3a show an increase in the percentage of cells expressing phospho-histone H3 as compared to controls. To test the proliferative effect of Wnt-3a in vivo, we ectopically expressed Wnt-3a in chick neural tubes via electroporation. Consistent with previous studies, ectopic expression of Wnt-3a in vivo results in a mediolateral expansion of the dermomyotome and myotome. We now show that proliferation of dorsal/ dermomyotomal cells is significantly enhanced by ectopic Wnt-3a. Collectively, our explant and in vivo studies indicate that an increase in proliferation plays an important role in the expansion of the dermomyotome and myotome in Wnt-3a-treated embryos. Furthermore, our results demonstrate that small changes in proliferation can dramatically influence patterning and morphogenesis. Keywords: Wnt-3a; Chick; Explant; Somite; Myogenesis; Dermomyotome; Myotome; Proliferation; Pax-1; Pax-3; Pax-7; MyoD; Myf-5; Myosin heavy chain (MHC); Apoptosis; [beta]-Catenin

Immunohistochemistry of cultured adult rat fibers reveals high levels of temporal expression of MyoD in the developing satellite cells during myogenesis. The myogenesis resembles the sequential expression of sarcomeric proteins such as alpha-smooth muscle actin and developmental sarcomeric myosin heavy chains. Basic fibroblast growth factor regulates the number of developing satellite cells.

Experiments conducted to determine the role of platelet-derived growth factor (PGDF) during embryogenesis revealed that this mitogen increases the production of chicken myoblasts specially during the late stages of development. The rate of expression of PGDF receptors was measured using myogenic clones from chick embryos. Higher levels of PGDF binding were observed in the later stages than in earlier stages of development.

On 19-21 November 2020, the meeting of the 30 years of the Padova Muscle Days was virtually held while the SARS-CoV-2 epidemic was hitting the world after a seemingly quiet summer. During the 2020-2021 winter, the epidemic is still active, despite the start of vaccinations. The organizers hope to hold the 2021 Padua Days on Myology and Mobility Medicine in a semivirtual form (2021 S-V PDM3) from May 26 to May 29 at the Thermae of Euganean Hills, Padova, Italy. Here the program and the Collection of Abstracts are presented. Despite numerous world problems, the number of submitted/selected presentations (lectures and oral presentations) has increased, prompting the organizers to extend the program to four dense days. [ABSTRACT FROM AUTHOR]