Transcriptional regulation of acetylcholinesterase-associated collagen ColQ in fast- and slow-twitch muscle fibers

Research progress on regulating factors of muscle fiber heterogeneity in poultry: a review

Control of meat quality traits is an important goal of any farm animal production, including poultry. A better understanding of the biochemical properties of muscle fiber properties that drive muscle development and ultimately meat quality constitutes one of the major challenging topics in animal production and meat science. In this paper, the existing classification methods of skeletal muscle fibers in poultry were reviewed and the relationship between contractile and metabolic characteristics of muscle fibers and poultry meat quality was described. Finally, a comprehensive review of multiple potential factors affecting muscle fiber distribution and conversion is presented, including breed, sex, hormones, growth performance, diet, muscle position, exercise, and ambient temperature. We emphasize that knowledge of muscle fiber typing is essential to better understand how to control muscle characteristics throughout the life cycle of animals to better manage the final quality of poultry meat.

Gene Expression Profile at the Motor Endplate of the Neuromuscular Junction of Fast-Twitch Muscle

The neuromuscular junction (NMJ) is a prototypic chemical synapse between the spinal motor neuron and the motor endplate. Gene expression profiles of the motor endplate are not fully elucidated. Collagen Q (ColQ) is a collagenic tail subunit of asymmetric forms of acetylcholinesterase and is driven by two distinct promoters. pColQ1 is active throughout the slow-twitch muscle, whereas pColQ1a is active at the motor endplate of fast-twitch muscle. We made a transgenic mouse line that expresses nuclear localization signal (NLS)-attached Cre recombinase under the control of pColQ1a (pColQ1a-Cre mouse). RiboTag mouse expresses an HA-tagged ribosomal subunit, RPL22, in cells expressing Cre recombinase. We generated pColQ1a-Cre:RiboTag mouse, and confirmed that HA-tagged RPL22 was enriched at the NMJ of tibialis anterior (TA) muscle. Next, we confirmed that Chrne and Musk that are specifically expressed at the NMJ were indeed enriched in HA-immunoprecipitated (IP) RNA, whereas Sox10 and S100b, markers for Schwann cells, and Icam1, a marker for vascular endothelial cells, and Pax3, a marker for muscle satellite cells, were scarcely detected. Gene set enrichment analysis (GSEA) of RNA-seq data showed that “phosphatidylinositol signaling system” and “extracellular matrix receptor interaction” were enriched at the motor endplate. Subsequent analysis revealed that genes encoding diacylglycerol kinases, phosphatidylinositol kinases, phospholipases, integrins, and laminins were enriched at the motor endplate. We first characterized the gene expression profile under translation at the motor endplate of TA muscle using the RiboTag technique. We expect that our gene expression profiling will help elucidate molecular mechanisms of the development, maintenance, and pathology of the NMJ.

Transcriptional activity of acetylcholinesterase gene is regulated by DNA methylation during C2C12 myogenesis

The expression of acetylcholinesterase (AChE), an enzyme hydrolyzes neurotransmitter acetylcholine at vertebrate neuromuscular junction, is regulated during myogenesis, indicating the significance of muscle intrinsic factors in controlling the enzyme expression. DNA methylation is essential for temporal control of myogenic gene expression during myogenesis; however, its role in AChE regulation is not known. The promoter of vertebrate ACHE gene carries highly conserved CG-rich regions, implying its likeliness to be methylated for epigenetic regulation. A DNA methyltransferase inhibitor, 5-azacytidine (5-Aza), was applied onto C2C12 cells throughout the myotube formation. When DNA methylation was inhibited, the promoter activity, transcript expression and enzymatic activity of AChE were markedly increased after day 3 of differentiation, which indicated the putative role of DNA methylation. By bisulfite pyrosequencing, the overall methylation rate was found to peak at day 3 during C2C12 cell differentiation; a SP1 site located at -1826bp upstream of mouse ACHE gene was revealed to be heavily methylated. The involvement of transcriptional factor SP1 in epigenetic regulation of AChE was illustrated here: (i) the SP1-driven transcriptional activity was increased in 5-Aza-treated C2C12 culture; (ii) the binding of SP1 onto the SP1 site of ACHE gene was fully blocked by the DNA methylation; and (iii) the sequence flanking SP1 sites of ACHE gene was precipitated by chromatin immuno-precipitation assay. The findings suggested the role of DNA methylation on AChE transcriptional regulation and provided insight in elucidating the DNA methylation-mediated regulatory mechanism on AChE expression during muscle differentiation.

Dissociation of transcription, translation, and assembly of collagen-tailed acetylcholinesterase in skeletal muscle

The synaptic form of acetylcholinesterase (AChE) in skeletal muscle ColQ-AChE derives from two separate genes encoding the catalytic and the non-catalytic collagenic tail (ColQ) subunits, respectively. ColQ-AChE expression is regulated by muscle activity; however, how this regulation takes place in skeletal muscle remains poorly understood. In this study, we overexpressed or knocked down ColQ expression in skeletal muscle and found that the level of this non-catalytic component by itself was sufficient to change the levels of total AChE activity by promoting assembly of higher order oligomeric forms including the collagen-tailed forms. These results initially suggested that ColQ could be limiting in the assembly of synaptic ColQ-AChE during development and differentiation. We then determined the levels of ColQ protein and ColQ mRNA during primary quail muscle cell development and differentiation in culture (QMCs) and as a function of muscle activity. Surprisingly, we found dissociation between transcription and translation of the non-catalytic subunit from its assembly into ColQ-AChE. Furthermore, we found that the vast majority of the steady state ColQ molecules in mature quail muscle cultures are not assembled into ColQ-AChE, suggesting that they are either rapidly degraded or have alternative function(s).

Restricted localization of proline-rich membrane anchor (PRiMA) of globular form acetylcholinesterase at the neuromuscular junctions--contribution and expression from motor neurons

The expression and localization of the proline-rich membrane anchor (PRiMA), an anchoring protein of tetrameric globular form acetylcholinesterase (G(4) AChE), were studied at vertebrate neuromuscular junctions. Both muscle and motor neuron contributed to this synaptic expression pattern. During the development of rat muscles, the expression of PRiMA and AChE(T) and the enzymatic activity increased dramatically; however, the proportion of G(4) AChE decreased. G(4) AChE in muscle was recognized specifically by a PRiMA antibody, indicating the association of this enzyme with PRiMA. Using western blot and ELISA, both PRiMA protein and PRiMA-linked G(4) AChE were found to be present in large amounts in fast-twitch muscle (e.g. tibialis), but in relatively low abundance in slow-twitch muscle (e.g. soleus). These results indicate that the expression level of PRiMA-linked G(4) AChE depends on muscle fiber type. In parallel, the expression of PRiMA, AChE(T) and G(4) AChE also increased in the spinal cord during development. Such expression in motor neurons contributed to the synaptic localization of G(4) AChE. After denervation, the expression of PRiMA, AChE(T) and G(4) AChE decreased markedly in the spinal cord, and in fast- and slow-twitch muscles.

Calcitonin gene-related peptide induces the expression of acetylcholinesterase-associated collagen ColQ in muscle: a distinction in driving two different promoters between fast- and slow-twitch muscle fibers

The presence of a collagenous protein (ColQ) characterizes the collagen-tailed forms of acetylcholinesterase at vertebrate neuromuscular junctions (nmjs). Two ColQ transcripts as ColQ-1 and ColQ-1a, driven by two promoters: pColQ-1 and pColQ-1a, were found in mammalian slow- and fast-twitch muscles, respectively, which have distinct expression pattern in different muscle fibers. In this study, we show the differential expression of CoQ in different muscles is triggered by calcitonin gene-related peptide (CGRP), a known motor neuron-derived factor. Application of CGRP, or dibutyryl-cAMP (Bt(2)-cAMP), in cultured myotubes induced the expression of ColQ-1a transcript and promoter activity; however, the expression of ColQ-1 transcript did not respond to CGRP or Bt(2)-cAMP. The CGRP-induced gene activation was blocked by an adenylyl cyclase inhibitor or a dominant negative mutant of cAMP-responsive element (CRE) binding protein (CREB). Two CRE sites were mapped within the ColQ-1a promoter, and mutations of the CRE sites abolished the response of CGRP or Bt(2)-cAMP. In parallel, CGRP receptor complex was dominantly expressed at the nmjs of fast muscle but not of slow muscle. These results suggested that the expression of ColQ-1a at the nmjs of fast-twitch muscle was governed by a CGRP-mediated cAMP signaling mechanism.

Regulation of a transcript encoding the proline-rich membrane anchor of globular muscle acetylcholinesterase. The suppressive roles of myogenesis and innervating nerves

The transcriptional regulation of proline-rich membrane anchor (PRiMA), an anchoring protein of tetrameric globular form acetylcholinesterase (G(4) AChE), was revealed in muscle during myogenic differentiation under the influence of innervation. During myotube formation of C2C12 cells, the expression of AChE(T) protein and the enzymatic activity were dramatically increased, but the level of G(4) AChE was relatively decreased. This G(4) AChE in C2C12 cells was specifically recognized by anti-PRiMA antibody, suggesting the association of this enzyme with PRiMA. Reverse transcription-PCR analysis revealed that the level of PRiMA mRNA was reduced during the myogenic differentiation of C2C12 cells. Overexpression of PRiMA in C2C12 myotubes significantly increased the production of G(4) AChE. The oligomerization of G(4) AChE, however, did not require the intracellular cytoplasmic tail of PRiMA. After overexpressing the muscle regulatory factors, myogenin and MyoD, the expressions of PRiMA and G(4) AChE in cultured myotubes were markedly reduced. In addition, calcitonin gene-related peptide, a known motor neuron-derived factor, and muscular activity were able to suppress PRiMA expression in muscle; the suppression was mediated by the phosphorylation of a cAMP-responsive element-binding protein. In accordance with the in vitro results, sciatic nerve denervation transiently increased the expression of PRiMA mRNA and decreased the phosphorylation of cAMP-responsive element-binding protein as well as its activator calcium/calmodulin-dependent protein kinase II in muscles. Our results suggest that the expression of PRiMA, as well as PRiMA-associated G(4) AChE, in muscle is suppressed by muscle regulatory factors, muscular activity, and nerve-derived trophic factor(s).