Brain Res Mol Brain Res 67:18C27. mRNA in both muscles. A reduction in AChR protein was documented in line with the above mRNA results. Evidence of partial denervation was found in the sternomastoid but not the tibialis anterior. Thus, myofiber ERK1/2 are differentially required for the maintenance of myofibers (2-Hydroxypropyl)-β-cyclodextrin and neuromuscular synapses in adult mice. INTRODUCTION Mitogen-activated protein kinases (MAPKs) are components of intracellular signaling modules that control a myriad of cellular processes. MAPK modules consist of 3 core protein kinase components. The most downstream is the actual MAPK, an S/T kinase that (2-Hydroxypropyl)-β-cyclodextrin phosphorylates the transcription factors, cytoskeletal elements, or other kinases that are the targets of regulation by signaling cascades started at the cell surface. A MAPK is usually activated by an upstream MAPK kinase (MAP2K), which, in turn, is activated by a MAP2K kinase (MAP3K). MAP3Ks are usually at the receiving end of signals derived from small, monomeric GTPases such as the Ras family or by other more intricate mechanisms (1). In mammalian cells, the prototypical MAPK module is composed of the MAPKs extracellular signal-regulated kinases 1 and 2 (ERK1/2), the MAP2Ks MEK1/2, and the MAP3K Raf. ERK1/2 regulate normal cellular responses to multiple growth factors and cytokines in proliferation, differentiation, and apoptosis (2, 3). Multiple studies suggest an important role for the Ras-ERK1/2 pathway in the development, normal maintenance, aging, and pathology of mammalian skeletal muscle. Thus, ERK1/2 activity has both stimulatory and inhibitory functions in the differentiation of cultured skeletal myotubes that vary with the stage of this protracted process (4,C8). (2-Hydroxypropyl)-β-cyclodextrin ERK1/2 have been implicated in the maintenance of adult skeletal muscle mass (9) and, seemingly paradoxically, in the control of both the fast-twitch (10) and the slow-twitch (11) fiber type phenotypes. Alterations in levels of ERK1/2 activity in aging rodent muscle correlate with sarcopenia (12), the loss of muscle mass and strength that occurs with aging (13). Ras-ERK1/2 pathway activity dysregulation underlies the pathology of neuromuscular diseases such as autosomal Emery-Dreifuss muscular dystrophy (14) and of the RASopathies, a group of rare genetic diseases with accompanying skeletal muscle abnormalities (15,C17). Our own work with cultured myotubes (18) suggests a modulatory role for ERK1/2 on the activity of agrin (19), a key synaptogenic factor in the formation and maintenance of the neuromuscular junction (2-Hydroxypropyl)-β-cyclodextrin (NMJ), the synapse between a motoneuron and a skeletal muscle fiber (20). and studies implicated ERK1/2 in the control of synapse-specific expression of acetylcholine receptor (AChR) subunit genes at the NMJ, particularly of have been reported to date. We combined a germ line mutant with Cre-loxP inactivation of in skeletal muscle to produce, for the first time, mice lacking ERK1/2 selectively in skeletal myofibers. We report that ERK1/2 are required for the maintenance of myofibers and NMJs in adult animals. MATERIALS AND METHODS Ethics statement. Care and treatment of all animals followed the National Research Council’s (24) and were approved by the Institutional Animal Care and Use Committee of Texas A&M University under animal use protocol 2012-168. Mice and genotyping. The Cre driver mice in which Cre is under the control of the human -skeletal muscle actin promoter are represented as floxed allele is usually represented as and mice from The Rabbit Polyclonal to THBD Landreth Lab, Case Western Reserve University. These crosses were used to generate experimental animals as follows. (detection of the wild type and null allele), 5-GTATCTTGGGTTCCCCATCC-3, 5-GGGGAACTTCCTGACTAGGG-3, and 5-GCTCCATGTCGAAGGTGAAT-3; and (detection of.