ABSTRACT
Recent data have shown that preservation of the neuromuscular junction (NMJ) after traumatic nerve injury helps to improve functional recovery with surgical repair via matrix metalloproteinase-3 (MMP3) blockade. As such, we sought to explore additional pathways that may augment this response. Wnt3a has been shown to inhibit acetylcholine receptor (AChR) clustering via ß-catenin-dependent signaling in the development of the NMJ. Therefore, we hypothesized that Wnt3a and ß-catenin are associated with NMJ destabilization following traumatic denervation. A critical size nerve defect was created by excising a 10-mm segment of the sciatic nerve in mice. Denervated muscles were then harvested at multiple time points for immunofluorescence staining, quantitative real-time PCR, and western blot analysis for Wnt3a and ß-catenin levels. Moreover, a novel Wnt/ß-catenin transgenic reporter mouse line was utilized to support our hypothesis of Wnt activation after traumatic nerve injury. The expression of Wnt3a mRNA was significantly increased by 2 weeks post-injury and remained upregulated for 2 months. Additionally, ß-catenin was activated at 2 months post-injury relative to controls. Correspondingly, immunohistochemical analysis of denervated transgenic mouse line TCF/Lef:H2B-GFP muscles demonstrated that the number of GFP-positive cells was increased at the motor endplate band. These collective data support that post-synaptic AChRs destabilize after denervation by a process that involves the Wnt/ß-catenin pathway. As such, this pathway serves as a potential therapeutic target to prevent the motor endplate degeneration that occurs following traumatic nerve injury.
Subject(s)
Muscle Denervation , Neuromuscular Junction/injuries , Wnt Proteins/metabolism , Wnt Signaling Pathway , beta Catenin/metabolism , Animals , Cell Line , Male , Mice, 129 Strain , Mice, Transgenic , Muscle Denervation/methods , Neuromuscular Junction/metabolism , Receptors, Cholinergic/metabolism , Wnt Signaling Pathway/physiologyABSTRACT
Small chromosomal deletions [Df(3R)eR-1 and Df(3R)eP] with intact hsromega transcription units but with variable deletions of the upstream region were used to map the upstream regions that regulate heat shock and amide responsivity of the 93D puff (hsromega locus) in salivary glands of late third instar larvae of Drosophila melanogaster. The Df(3R)eP deletion, generated by a P-element mobilization screen, removed the 93B6-7 to 93D3-5 cytogenetic region. [3H]uridine-labeled transcription autoradiograms revealed that normal developmental and heat shock-induced expression of the 93D puff remained unaffected in both the deficiency chromosomes. However, the amide responsivity of the 93D site was lost on the Df(3R)eP homolog while the Df(3R)eR-1 homolog responded normally to amides. Southern hybridizations with a series of upstream probes mapped the distal breakpoint of the Df(3R)eP deletion between -22 kb and -23 kb of the hsromega transcription unit. Since the distal breakpoint of Df(3R)eR-1 is at about -45 kb upstream of the hsromega gene it is inferred that the amide response element(s) that modulate the specific transcriptional activation of the 93D puff following treatment of salivary glands with a variety of amides is/are located in the -22 kb to about -45 kb upstream interval. The Df(3R)eP and Df(3R)eR-1 deletions also abolished dosage compensation at the 93D locus as well as the effect of beta-alanine levels on its heat shock inducibility.
Subject(s)
5' Untranslated Regions/genetics , Amides/pharmacology , Chromosome Mapping/methods , Drosophila Proteins , Drosophila melanogaster/genetics , Genes, Insect , Heat-Shock Response/genetics , 5' Untranslated Regions/drug effects , Animals , DNA-Binding Proteins/genetics , Genes, Insect/drug effects , Mutation , Transcription, Genetic , Translocation, GeneticABSTRACT
We report here that 3-aminobenzamide and other amides, such as formamide, acetamide and nicotinamide, specifically induce a high rate of transcription at the 93D puff (the hsr omega heat shock gene) in polytene chromosomes of Drosophila melanogaster. Other chemicals, such as benzamide, colchicine, thiamphenicol and paracetamol, that are already known to specifically induce transcription at the hsr omega locus are also identified as amides. In view of the specific induction of the 93D puff by different amides and other data that demonstrate hsr omega transcription in response to benzamide and colchicine etc. to be independent of its heat shock induction, it appears likely that amides induce this locus through distinct regulatory elements that we propose to designate amide response elements (AREs).
