Identification of responsive cells in the developing somite supports a role for Β-catenin-dependent Wnt signaling in maintaining the DML myogenic progenitor pool

Somitic Β-catenin is involved in both maintaining a stem cell population and controlling myogenic differentiation. It is unclear how Β-catenin-dependent Wnt signaling accomplishes these disparate roles. The present study shows that only dorsal cells in the early somite respond to Β-catenin-dependent Wnt signaling and as the somites compartmentalize to form the dermomyotome and myotome, responding cells are detected primarily in the dorsomedial lip (DML). Forced activation of Wnt target genes in DML cells prevents their progeny from entering the myotome, while blocking activation allows myotomal entry. This suggests a role for Β-catenin-dependent/Wnt signaling in maintaining progenitor cells in the DML and that if Β-catenin-dependent/Wnt signaling is required to induce myogenesis, the response is transitory and rapidly down-regulated. Developmental Dynamics 239:222–236, 2010. © 2009 Wiley-Liss, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/64520/1/22098_ftp.pd

Ectopic Pax-3 Activates MyoD and Myf-5 Expression in Embryonic Mesoderm and Neural Tissue

AbstractTo understand how the skeletal muscle lineage is induced during vertebrate embryogenesis, we have sought to identify the regulatory molecules that mediate induction of the myogenic regulatory factors MyoD and Myf-5. In this work, we demonstrate that either signals from the overlying ectoderm or Wnt and Sonic hedgehog signals can induce somitic expression of the paired box transcription factorsPax-3 and Pax-7, concomitant with expression of Myf-5 and prior to that of MyoD. Moreover, infection of embryonic tissues in vitro with a retrovirus encoding Pax-3 is sufficient to induce expression of MyoDMyf-5, and myogenin in both paraxial and lateral plate mesoderm in the absence of inducing tissues as well as in the neural tube. Together, these findings imply that Pax-3 may mediate activation of MyoD and Myf-5 in response to muscle-inducing signals from either the axial tissues or overlying ectoderm and identify Pax-3 as a key regulator of somitic myogenesis

Wiring diagrams: regulatory circuits and the control of skeletal myogenesis

During the past year, targeted mutagenesis in mice has begun to clarify the roles of individual members of the MyoD family of myogenic regulators in vertebrate development. In this review, we discuss these studies both in the context of tissue interactions necessary to induce skeletal muscle precursor cells during embryogenesis and the molecular circuitry that regulates the terminal differential of these cells