Identification of the Neuromuscular Junction Transcriptome of Extraocular Muscle by Laser Capture Microdissection

Department of Cell and Developmental Biology, Pennsylvania Muscle Institute, School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
Investigative ophthalmology & visual science (Impact Factor: 3.4). 09/2010; 51(9):4589-99. DOI: 10.1167/iovs.09-4893
Source: PubMed

ABSTRACT To examine and characterize the profile of genes expressed at the synapses or neuromuscular junctions (NMJs) of extraocular muscles (EOMs) compared with those expressed at the tibialis anterior (TA).
Adult rat eyeballs with rectus EOMs attached and TAs were dissected, snap frozen, serially sectioned, and stained for acetylcholinesterase (AChE) to identify the NMJs. Approximately 6000 NMJs for rectus EOM (EOMsyn), 6000 NMJs for TA (TAsyn), equal amounts of NMJ-free fiber regions (EOMfib, TAfib), and underlying myonuclei and RNAs were captured by laser capture microdissection (LCM). RNA was processed for microarray-based expression profiling. Expression profiles and interaction lists were generated for genes differentially expressed at synaptic and nonsynaptic regions of EOM (EOMsyn versus EOMfib) and TA (TAsyn versus TAfib). Profiles were validated by using real-time quantitative polymerase chain reaction (qPCR).
The regional transcriptomes associated with NMJs of EOMs and TAs were identified. Two hundred seventy-five genes were preferentially expressed in EOMsyn (compared with EOMfib), 230 in TAsyn (compared with TAfib), and 288 additional transcripts expressed in both synapses. Identified genes included novel genes as well as well-known, evolutionarily conserved synaptic markers (e.g., nicotinic acetylcholine receptor (AChR) alpha (Chrna) and epsilon (Chrne) subunits and nestin (Nes).
Transcriptome level differences exist between EOM synaptic regions and TA synaptic regions. The definition of the synaptic transcriptome provides insight into the mechanism of formation and functioning of the unique synapses of EOM and their differential involvement in diseases noted in the EOM allotype.

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    • "LCM has also been applied to identify the unique expression profiles of specialized regions within complex cells. For example, LCM has been combined with RNA isolation and transcriptome analysis to identify specific transcripts and components of the neuromuscular junction [5,6]. In combination with liquid chromatography tandem mass spectrometry (LC-MS/MS), LCM has been extensively used, amongst others applications, to purify and profile cancer cells (for a review see [7]), profile plaques in neurological disease [8-11] or elucidate the expression profile of inclusion bodies within muscle fibres [12]. "
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    ABSTRACT: The myotendinous junction is a specialized structure of the muscle fibre enriched in mechanosensing complexes, including costameric proteins and core elements of the z-disc. Here, laser capture microdissection was applied to purify membrane regions from the myotendinous junctions of mouse skeletal muscles, which were then processed for proteomic analysis. Sarcolemma sections from the longitudinal axis of the muscle fibre were used as control for the specificity of the junctional preparation. Gene ontology term analysis of the combined lists indicated a statistically significant enrichment in membrane-associated proteins. The myotendinous junction preparation contained previously uncharacterized proteins, a number of z-disc costameric ligands (e.g., actinins, capZ, αB cristallin, filamin C, cypher, calsarcin, desmin, FHL1, telethonin, nebulin, titin and an enigma-like protein) and other proposed players of sarcomeric stretch sensing and signalling, such as myotilin and the three myomesin homologs. A subset were confirmed by immunofluorescence analysis as enriched at the myotendinous junction, suggesting that laser capture microdissection from muscle sections is a valid approach to identify novel myotendinous junction players potentially involved in mechanotransduction pathways.
    Proteome Science 05/2014; 12(25). DOI:10.1186/1477-5956-12-25 · 1.73 Impact Factor
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    • "Furthermore, EHD1−/− muscle fibers had normal NMJ morphology, histology, and function despite the deficient mice having a lower body mass and size. Muscle-wide expression of EHD1 was previously shown [30] by regional transcriptome profiling of laser capture microdissected synaptic and non-synaptic areas of rat TA skeletal muscle. "
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    ABSTRACT: Background Recycling of endosomes is important for trafficking and maintenance of proteins at the neuromuscular junction (NMJ). We have previously shown high expression of the endocytic recycling regulator Eps15 homology domain-containing (EHD)1 proteinin the Torpedo californica electric organ, a model tissue for investigating a cholinergic synapse. In this study, we investigated the localization of EHD1 and its paralogs EHD2, EHD3, and EHD4 in mouse skeletal muscle, and assessed the morphological changes in EHD1−/− NMJs. Methods Localization of the candidate NMJ protein EHD1 was assessed by confocal microscopy analysis of whole-mount mouse skeletal muscle fibers after direct gene transfer and immunolabeling. The potential function of EHD1 was assessed by specific force measurement and α-bungarotoxin-based endplate morphology mapping in EHD1−/− mouse skeletal muscle. Results Endogenous EHD1 localized to primary synaptic clefts of murine NMJ, and this localization was confirmed by expression of recombinant green fluorescent protein labeled-EHD1 in murine skeletal muscle in vivo. EHD1−/− mouse skeletal muscle had normal histology and NMJ morphology, and normal specific force generation during muscle contraction. The EHD 1–4 proteins showed differential localization in skeletal muscle: EHD2 to muscle vasculature, EHD3 to perisynaptic regions, and EHD4 to perinuclear regions and to primary synaptic clefts, but at lower levels than EHD1. Additionally, specific antibodies raised against mammalian EHD1-4 recognized proteins of the expected mass in the T. californica electric organ. Finally, we found that EHD4 expression was more abundant in EHD1−/− mouse skeletal muscle than in wild-type skeletal muscle. Conclusion EHD1 and EHD4 localize to the primary synaptic clefts of the NMJ. Lack of obvious defects in NMJ structure and muscle function in EHD1−/− muscle may be due to functional compensation by other EHD paralogs.
    Skeletal Muscle 09/2012; 2(1):19. DOI:10.1186/2044-5040-2-19
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    ABSTRACT: Amyotrophic lateral sclerosis (ALS) is a progressive, lethal neurodegenerative disorder characterised by selective loss of motor neurons with accompanying muscle paralysis and respiratory failure. Despite progressive paralysis in trunk and extremity muscles, disturbed eye motility is not a hallmark of ALS. Extraocular muscles (EOMs) of terminal ALS patients show far less morphological signs of disease than their limb muscles. One of the earliest signs of the disease in the transgenic G93A SOD1 mouse model of ALS is loss of motor neuron contact at the neuromuscular junctions (NMJ) in limb muscles. We used immunohistochemistry to identify NMJs and evaluate innervation in EOMs and limb muscles of G93A mice. In G93A limb muscles, loss of axonal contact was seen in 6-82 percent of the NMJs. On the contrary, the degree of endplate occupancy in the EOMs did not differ between transgenic mice and wild-type controls. We propose that EOM-specific properties make these muscles more resistant to the underlying pathophysiological process of ALS and that the EOMs are a useful model to advance our understanding of ALS.
    Frontiers in bioscience (Scholar edition) 06/2012; 4(4):1547-55. DOI:10.2741/S351
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