MicroRNAs are well known to mediate translational repression and mRNA degradation in the cytoplasm. Various microRNAs have also been detected in membrane-compartmentalized organelles, but the functional significance has remained elusive. Here we report that miR-1, a microRNA specifically induced during myogenesis, efficiently enters the mitochondria where it unexpectedly stimulates, rather than represses, the translation of specific mitochondrial genome-encoded transcripts. We show that this positive effect requires specific miR:mRNA base-pairing and Ago2, but not its functional partner GW182, which is excluded from the mitochondria. We provide evidence for the direct action of Ago2 in mitochondrial translation by CLIP-seq, functional rescue with mitochondria-targeted Ago2, and selective inhibition of the microRNA machinery in the cytoplasm. These findings unveil a positive function of microRNA in mitochondrial translation and suggest a highly coordinated myogenic program via miR-1 mediated translational stimulation in the mitochondria and repression in the cytoplasm.

The epidermal growth factor receptor (EGF-R) plays an important role in development and cell differentiation, and homologues of EGF-R have been identified in a broad range of vertebrate and invertebrate organisms. This work concerns the functional characterization of SER, the EGF-R-like molecule previously identified in the helminth parasite Schistosoma mansoni The epidermal growth factor receptor (EGF-R) 1 is a major key mediator of cell communication during animal development and homeostasis. EGF-R was the first receptor tyrosine kinase to be cloned (1), and its structure and activation pathways have been studied extensively. EGF-R represents the archetype of receptor tyrosine kinase with an extracellular ligand-binding part with two cysteine-rich repeats and an intracellular domain containing tyrosine kinase activity (2). In mammals, four isoforms of EGF-R have been characterized (EGF-R/ErbB-1, HER2/ErbB-2, HER3/ErbB-3, and HER4/ ErbB-4), and a number of different ligands, including epidermal growth factor (EGF)-like molecules, can selectively bind each isoform (3). Ligand binding activates the receptor by inducing the formation of homo-heterodimers. Dimerization triggers trans-phosphorylation and subsequent autophosphorylation of receptor molecules on tyrosine residues that provide docking sites for diverse effector and adaptor proteins. These partners (Grb2/Sos, p85-PI3K, PLC␥, and JAK) are active in different signal transduction cascades, such as the mitogenactivated protein kinase (MAPK), phosphoinositol 3-kinase, antiapoptotic kinase Akt, and several transcriptional regulatory pathways (reviewed in Ref. 4). Different homodimer-heterodimer combinations formed by EGF-R family members drive a complex signaling network within the MAPK pathway. The ERK pathway is the most recurrent and is mainly responsible for the mitogenic action of EGF receptors. Dysregulation of EGF-R signaling is therefore strongly oncogenic, and the direct implication of EGF-R isoforms in various cancers has been widely demonstrated. For this reason, EGF-R currently represents one of the major drug targets in human cancer therapy (5).In invertebrates, EGF-R isoforms appeared to be expressed in more limited numbers. A single isoform has been characterized in Caenorhabditis elegans (LET-23) (6) as well as in Drosophila melanogaster (DER) (7,8). A single cognate ligand (LIN-3) would be present in the worm (9), and four distinct cognate ligands (Vein, Gurken, Spitz, and Argos) would be present in the fly (10). These observations indicated that the EGF-R signaling module has grown in complexity from invertebrates to mammals. However, except for C. elegans and D. melanogaster models, few data are available at present about the role of the EGF-R family in invertebrate development.SER, the Schistosoma mansoni EGF-R homologue, is one of the three receptor tyrosine kinases that have been characterized in this trematode parasite (11,12). SER is present predominantly in schistosome muscles, suggesting that it could

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Degummed silk filament was pulverized with a home‐made machine to obtain silk fibroin (SF) powder, and the structure, morphology, and particle size of the SF powder were investigated. The individual spherical particles and aggregates with different morphology of silk fibroin coexisted in water. A waterborne polyurethane (WPU) aqueous dispersion was blended with the SF powder to prepare novel blended materials with improved physical properties. The average particle size and zeta potential of the WPU/SF aqueous dispersions were characterized. The result showed that the WPU/SF dispersion with higher SF content exhibited a less negative zeta potential and a larger average particle size. Furthermore, the effect of SF content on the morphology, miscibility, and mechanical properties of the resulting blended films was studied by scanning electron microscopy, wide‐angle X‐ray diffraction, dynamic mechanical thermal analysis, and tensile testing. The films showed an improved Young's modulus and tensile strength from 0.3 to 33.8 MPa, and 0.6 to 5.2 MPa, respectively, with the increasing of SF up to a content of 26 wt %. The negative charges in the periphery and the small particle size made a good effort on dispersing SF powder into the WPU matrix as small aggregates, and the SF powder led to the efficient strengthening of WPU materials. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 940–950, 2010