MyoD- and nerve-dependent maintenance of MyoD expression in mature muscle fibres acts through the DRR/PRR element

<p>Abstract</p> <p>Background</p> <p>MyoD is a transcription factor implicated in the regulation of adult muscle gene expression. Distinguishing the expression of <it>MyoD </it>in satellite myoblasts and muscle fibres has proved difficult <it>in vivo </it>leading to controversy over the significance of <it>MyoD </it>expression within adult innervated muscle fibres. Here we employ the <it>MD6.0-lacZ </it>transgenic mouse, in which the 6 kb proximal enhancer/promoter (DRR/PRR) of <it>MyoD </it>drives <it>lacZ</it>, to show that MyoD is present and transcriptionally active in many adult muscle fibres.</p> <p>Results</p> <p>In culture, <it>MD6.0-lacZ </it>expresses in myotubes but not myogenic cells, unlike endogenous <it>MyoD</it>. Reporter expression <it>in vivo </it>is in muscle fibre nuclei and is reduced in <it>MyoD </it>null mice. The <it>MD6.0-lacZ </it>reporter is down-regulated both in adult muscle fibres by denervation or muscle disuse and in cultured myotubes by inhibition of activity. Activity induces and represses <it>MyoD </it>through the DRR and PRR, respectively. During the postnatal period, accumulation of β-galactosidase correlates with maturation of innervation. Strikingly, endogenous <it>MyoD </it>expression is up-regulated in fibres by complete denervation, arguing for a separate activity-dependent suppression of <it>MyoD </it>requiring regulatory elements outside the DRR/PRR.</p> <p>Conclusion</p> <p>The data show that <it>MyoD </it>regulation is more complex than previously supposed. Two factors, MyoD protein itself and fibre activity are required for essentially all expression of the 6 kb proximal enhancer/promoter (DRR/PRR) of <it>MyoD </it>in adult fibres. We propose that modulation of MyoD positive feedback by electrical activity determines the set point of <it>MyoD </it>expression in innervated fibres through the DRR/PRR element.</p

Distinct roles for Pax7 and Pax3 in adult regenerative myogenesis

We assessed viable Pax7−/− mice in 129Sv/J background and observed reduced growth and marked muscle wasting together with a complete absence of functional satellite cells. Acute injury resulted in an extreme deficit in muscle regeneration. However, a small number of regenerated myofibers were detected, suggesting the presence of residual myogenic cells in Pax7-deficient muscle. Rare Pax3+/MyoD+ myoblasts were recovered from Pax7−/− muscle homogenates and cultures of myofiber bundles but not from single myofibers free of interstitial tissues. Finally, we identified Pax3+ cells in the muscle interstitial environment and demonstrated that they coexpressed MyoD during regeneration. Sublaminar satellite cells in hind limb muscle did not express detectable levels of Pax3 protein or messenger RNA. Therefore, we conclude that interstitial Pax3+ cells represent a novel myogenic population that is distinct from the sublaminar satellite cell lineage and that Pax7 is essential for the formation of functional myogenic progenitors from sublaminar satellite cells

Developing Educational Resources to Advance Umbilical Cord Blood Banking and Research: A Canadian Perspective

In 2013 Canadian Blood Services (CBS) launched the National Public Cord Blood Bank (NPCBB), a program to collect, process, test, and store cord blood units donated for use in transplantation. A key component of the creation of the NPCBB is the establishment of a program that enables cord blood not suitable for banking or transplantation to be used for biomedical research purposes. Along with the development of processes and policies to manage the NPCBB and the cord blood research program, CBS—in collaboration with researchers from the Stem Cell Network—have also developed educational tools to provide relevant information for target audiences to aid implementation and operation. We describe here one of these tools, the REB Primer on Research and Cord Blood Donation (the Primer), which highlights key ethical and legal considerations and identifies Canadian documents that are relevant to the use of cord blood in biomedical research. The Primer also introduces the NPCBB and describes the systems CBS is implementing to address ethical issues. The Primer is intended to assist research ethics boards in evaluating the ethical acceptability of research protocols, to facilitate harmonized decision-making by providing a common reference, and to highlight the role of research ethics boards in governance frameworks. With the Primer we hope to illustrate how the development of such educational tools can facilitate the ethical implementation and governance of programs related to stem cell research in Canada and abroad. En 2013, la Société canadienne du sang (SCS) a lancé la Banque publique nationale de sang de cordon ombilical (BPNSCO) : un programme de prélèvement, de traitement, d’analyse et d’entreposage d’unités de sang de cordon ombilical ayant fait l’objet d’un don pour une utilisation dans le cadre de greffes. La mise sur pied d’un programme permettant l’utilisation, aux fins de la recherche biomédicale, du sang de cordon ombilical ne pouvant être mis en banque ni être utilisé pour des greffes constitue une composante clé de la création de la BPNSCO. Conjointement avec l’élaboration de processus et de politiques permettant la gestion de la BPNSCO et du programme de recherche sur le sang de cordon ombilical, la SCS (en collaboration avec les chercheurs du Réseau de cellules souches) ont également conçu des outils pédagogiques permettant l’offre de renseignements pertinents aux populations visées, de façon à faciliter la mise en œuvre et la gestion des activités. Nous décrivons ici l’un de ces outils : le REB Primer on Research and Cord Blood Donation (le « guide »). Ce « guide » souligne les enjeux éthiques et légaux clés, et identifie les documents canadiens pertinents en ce qui concerne l’utilisation de sang de cordon ombilical aux fins de la recherche biomédicale. Ce « guide » présente également la BPNSCO et décrit les systèmes qui sont mis en œuvre par la SCS pour répondre aux questions éthiques. Il a pour but d’aider les conseils d’éthique de la recherche à évaluer l’acceptabilité éthique des protocoles de recherche, de faciliter l’harmonisation des processus décisionnels en offrant un cadre de référence commun et de souligner le rôle des conseils d’éthique de la recherche dans les cadres de gouvernance. Grâce à ce « guide », nous espérons illustrer la façon dont l’élaboration de tels outils pédagogiques peut faciliter la mise en œuvre et la gestion éthiques de programmes associés à la recherche sur les cellules souches au Canada et à l’étranger