S studied. Two recent studies have reported the involvement of microRNAs in controlling axon development from embryonic neurons in vitro (Dajas-Bailador et al. 2012; Franke et al. 2012). In mature animals, 1 study discovered that sensory axon regeneration in vivo was impaired in animals lacking the Dicer protein, that is essential for microRNA processing (Wu et al. 2012), suggesting that microRNAs are potential novel regulators of axon regeneration. Certainly, several genetic profiling studies (Strickland et al. 2011; Zhang et al. 2011; Zhou et al. 2011) have shown that the expression levels of numerous microRNAs are changed in adult mouse sensory neurons following the peripheral nerve injury, which leads to enhanced intrinsic axon development capacity and robust axon regeneration. Having said that, to date, no study has ever reported the roles of microRNAs in the regulation of mammalian axon regeneration in vivo. Similarly, we know veryGENES Development 27:1473483 2013 by Cold Spring Harbor Laboratory Press ISSN 0890-9369/13; www.genesdev.orgLiu et al.small in regards to the roles of histone modification in axon regeneration. To our understanding, to date, only two recent studies have shown the involvement of histone acetyltransferase p300 inside the regulation of axon regeneration (Gaub et al. 2010, 2011). Here, we report that microRNA-138 (miR-138), a very expressed microRNA inside the nervous program (Obernosterer et al.Lonafarnib 2006), functions to regulate axon growth for the duration of development and regeneration by acting as a molecular repressor. We additional recognize the NAD-dependent histone deacetylase (HDAC) SIRT1 as a downstream molecular target of miR-138.Fluticasone (propionate) Extra importantly, we offer the first in vivo proof that miR-138 and SIRT1 function to suppress and promote mammalian axon regeneration, respectively.PMID:24179643 Interestingly, we found that SIRT1 also acts as a transcriptional repressor to directly suppress the expression of miR-138 in response to peripheral nerve injury. Collectively, we demonstrate that mammalian peripheral nerve injury results in robust axon regeneration by inducing the formation of a mutual adverse feedback loop amongst two epigenetic components: miR-138 and the HDAC SIRT1. Benefits miR-138 is developmentally regulated during cortical improvement and controls axon development of embryonic cortical neurons We 1st investigated whether miR-138 regulated axon growth applying cultured mouse embryonic cortical neurons, that are a well-established model system for studying axon development. Using mature microRNA-specific quantitative real-time PCR (qRT-PCR), we found that the expression amount of endogenous miR-138 gradually improved in the cortical tissues throughout development, reaching the highest level in adult animals (Fig. 1A). As cortical neurons lose their intrinsic capability to support axon growth right after maturation (Liu et al. 2012a), this outcome suggests that miR-138 may well be a adverse regulator of axon development. To test this idea, we transfected embryonic day 15 (E15) cortical neurons with either the miR-138 mimics, that are double-stranded oligonucleotides developed to mimic the function of endogenous mature microRNA, or the miR-138 inhibitor, which is RNA oligonucleotides with a novel secondary structure (hairpin) created to inhibit the biogenesis of endogenous microRNA (Dharmacon miRIDIAN microRNA reagents). Expression in the miR-138 mimics drastically increased the degree of miR-138 in neurons, whereas expression of the miR-138 inhibitor markedly decreased the amount of endogenous miR-138 (Fi.
