Cloning and developmental expression analysis of ltd-1, the Caenorhabditis elegans homologue of the mouse kyphoscoliosis (ky) gene

Transcriptome analysis of the gene expression of M. iliotibialis lateralis affected by dietary methionine restriction

Introduction: Methionine (Met) is an important amino acid related to the development of skeletal muscle. This study investigated the effects of dietary Met restriction on the gene expression of M. iliotibialis lateralis. Methods: A total of 84 day-old broiler chicks (Zhuanghe Dagu) with a similar initial body weight (207.62 ± 8.54 g) were used in this study. All birds were divided into two groups (CON; L-Met) based on the initial body weight. Each group consisted of six replicates with seven birds per replicate. The experimental period was 63 days (phase 1, days 1-21; phase 2, days 22-63). According to the nutritional requirements of Zhuanghe Dagu chickens, we provided a basal diet (0.39% Met levels during phase 1 and 0.35% Met levels during phase 2, as-fed basis) to the birds in the CON group, while we provided a Met-restricted diet (0.31% Met levels during phase 1 and 0.28% Met levels during phase 2, as-fed basis) to the birds in the L-Met group. The growth performance of broiler chicks and their M. iliotibialis lateralis development parameters were measured on days 21 and 63. Results and Discussion: In this study, dietary Met restriction did not affect the growth performance of broiler chicks but hindered the development of M. iliotibialis lateralis at both sampling timepoints. On the final day, three birds selected from each group (three from CON and three from L-Met) were used to obtain M. iliotibialis lateralis samples from leg muscle for further transcriptome analysis. Transcriptome analysis revealed that dietary Met restriction significantly upregulated 247 differentially expressed genes (DEGs) and downregulated 173 DEGs. Additionally, DEGs were mainly enriched in 10 pathways. Among DEGs, we observed that dietary Met restriction downregulated the expression of CSRP3, KY, FHL1, LMCD1, and MYOZ2 in M. iliotibialis lateralis. Therefore, we considered that dietary Met restriction had negative effects on the development of M. iliotibialis lateralis, and CSRP3, KY, FHL1, LMCD1, and MYOZ2 may serve as potential functional genes involved in this process.

Specific targeting of TGF-β family ligands demonstrates distinct roles in the regulation of muscle mass in health and disease

The transforming growth factor-β (TGF-β) network of ligands and intracellular signaling proteins is a subject of intense interest within the field of skeletal muscle biology. To define the relative contribution of endogenous TGF-β proteins to the negative regulation of muscle mass via their activation of the Smad2/3 signaling axis, we used local injection of adeno-associated viral vectors (AAVs) encoding ligand-specific antagonists into the tibialis anterior (TA) muscles of C57BL/6 mice. Eight weeks after AAV injection, inhibition of activin A and activin B signaling produced moderate (∼20%), but significant, increases in TA mass, indicating that endogenous activins repress muscle growth. Inhibiting myostatin induced a more profound increase in muscle mass (∼45%), demonstrating a more prominent role for this ligand as a negative regulator of adult muscle mass. Remarkably, codelivery of activin and myostatin inhibitors induced a synergistic response, resulting in muscle mass increasing by as much as 150%. Transcription and protein analysis indicated that this substantial hypertrophy was associated with both the complete inhibition of the Smad2/3 pathway and activation of the parallel bone morphogenetic protein (BMP)/Smad1/5 axis (recently identified as a positive regulator of muscle mass). Analyses indicated that hypertrophy was primarily driven by an increase in protein synthesis, but a reduction in ubiquitin-dependent protein degradation pathways was also observed. In models of muscular dystrophy and cancer cachexia, combined inhibition of activins and myostatin increased mass or prevented muscle wasting, respectively, highlighting the potential therapeutic advantages of specifically targeting multiple Smad2/3-activating ligands in skeletal muscle.

RNA sequencing identifies upregulated kyphoscoliosis peptidase and phosphatidic acid signaling pathways in muscle hypertrophy generated by transgenic expression of myostatin propeptide

Myostatin (MSTN), a member of the transforming growth factor-β superfamily, plays a crucial negative role in muscle growth. MSTN mutations or inhibitions can dramatically increase muscle mass in most mammal species. Previously, we generated a transgenic mouse model of muscle hypertrophy via the transgenic expression of the MSTN N-terminal propeptide cDNA under the control of the skeletal muscle-specific MLC1 promoter. Here, we compare the mRNA profiles between transgenic mice and wild-type littermate controls with a high-throughput RNA sequencing method. The results show that 132 genes were significantly differentially expressed between transgenic mice and wild-type control mice; 97 of these genes were up-regulated, and 35 genes were down-regulated in the skeletal muscle. Several genes that had not been reported to be involved in muscle hypertrophy were identified, including up-regulated myosin binding protein H (mybph), and zinc metallopeptidase STE24 (Zmpste24). In addition, kyphoscoliosis peptidase (Ky), which plays a vital role in muscle growth, was also up-regulated in the transgenic mice. Interestingly, a pathway analysis based on grouping the differentially expressed genes uncovered that cardiomyopathy-related pathways and phosphatidic acid (PA) pathways (Dgki, Dgkz, Plcd4) were up-regulated. Increased PA signaling may increase mTOR signaling, resulting in skeletal muscle growth. The findings of the RNA sequencing analysis help to understand the molecular mechanisms of muscle hypertrophy caused by MSTN inhibition.

Distinct roles of Rho1, Cdc42, and Cyk3 in septum formation and abscission during yeast cytokinesis

In yeast and animal cytokinesis, the small guanosine triphosphatase (GTPase) Rho1/RhoA has an established role in formation of the contractile actomyosin ring, but its role, if any, during cleavage-furrow ingression and abscission is poorly understood. Through genetic screens in yeast, we found that either activation of Rho1 or inactivation of another small GTPase, Cdc42, promoted secondary septum (SS) formation, which appeared to be responsible for abscission. Consistent with this hypothesis, a dominant-negative Rho1 inhibited SS formation but not cleavage-furrow ingression or the concomitant actomyosin ring constriction. Moreover, Rho1 is temporarily inactivated during cleavage-furrow ingression; this inactivation requires the protein Cyk3, which binds Rho1-guanosine diphosphate via its catalytically inactive transglutaminase-like domain. Thus, unlike the active transglutaminases that activate RhoA, the multidomain protein Cyk3 appears to inhibit activation of Rho1 (and thus SS formation), while simultaneously promoting cleavage-furrow ingression through primary septum formation. This work suggests a general role for the catalytically inactive transglutaminases of fungi and animals, some of which have previously been implicated in cytokinesis.

D-Hillarin, a novel W180-domain protein, affects cytokinesis through interaction with the septin family member Pnut

By database searches of the Drosophila genome project we have identified D-hil as the fly member of a novel family of W180-domain containing proteins. Immunocytochemistry demonstrated that D-hil is localized to the neuropil of the embryonic CNS, to the cellular cortex of dividing neuroblasts from larval brains, and that it is up-regulated in the cleavage furrow of S2 cells. We show that D-hil distribution overlaps extensively with that of the septin family member Pnut. Cross-immunoprecipitation experiments further indicated that the two proteins may be members of the same protein complex. Analysis of a severe hypomorphic P-element mutation in the D-hil locus suggested that D-hil is a nonessential protein. However, by creating double mutant flies we show that the D-hil locus acts as a modulator of Pnut function by increasing the level of polyploidy of neuroblasts in Pnut(KG00478)/Pnut(KG00478) larval brains. Based on these results we propose that D-hil may function as a regulator of septin function during cytokinesis in the developing nervous system.

Filamin C interacts with the muscular dystrophy KY protein and is abnormally distributed in mouse KY deficient muscle fibres

The KY protein has been implicated in a neuromuscular dystrophy in the mouse, but its role in muscle function remains unclear. Here, we show that KY interacts with several sarcomeric cytoskeletal proteins including, amongst others, filamin C and the slow isoform of the myosin-binding protein C. These interactions were confirmed in vitro and because of its central role in skeletal muscle disease, characterized in more detail for filamin C. A role for KY in regulating filamin C function in vivo is supported by the expression analysis of filamin C in the null ky mouse mutant, where distinct irregular subcellular localization of filamin C was found in subsets of muscle fibres, which appears to be a specific outcome of KY deficiency. Furthermore, KY shows protease activity in in vitro assays, and specific degradation of filamin C by KY is shown in transfected cells. Given the enzymatic nature of the KY protein, it is likely that some of the identified partners are catalytic substrates. These results suggest that KY is an intrinsic part of the protein networks underlying the molecular mechanism of several limb-girdle muscular dystrophies, particularly those where interactions between filamin C and disease causing proteins have been shown.

Molecular phenotyping of the mouse ky mutant reveals UCP1 upregulation at the neuromuscular junctions of dystrophic soleus muscle

The ky mutant mouse displays a muscular dystrophy that affects almost exclusively slow type muscles in which persistent muscle regeneration, neuromuscular junction instability and an absence of the hypertrophic response are prominent features. In order to gain insights into the pathogenesis of this muscular dystrophy we have undertaken RNA profiling of the extensor digitorum longus, a fast unaffected muscle, and the highly pathological soleus slow muscle, followed by further expression studies to validate the results. In dystrophic soleus, there is a coordinated change in the expression level of genes encoding energy transducing mitochondrial proteins and an increase in the expression of stretch response genes. Upregulation of uncoupling proteins 1 and 2 is a unique molecular signature of the ky muscular dystrophy and was further characterised at the protein level. Our results show a spatial and temporal association between disorganisation of acetylcholine receptor clusters and upregulation of uncoupling protein 1. There is also evidence of a breakdown of neuromuscular junction muscle-specific kinase-dependent signalling in adult mutant soleus. Sarcolemma-associated proteins implicated in muscular dystrophies revealed no differences on microarrays and were confirmed as normally distributed by immunofluorescence. Altogether, the data presented suggest that the ky muscular dystrophy develops by a distinctive pathogenic mechanism.

An Essential Role in Molting and Morphogenesis of Caenorhabditis elegans for ACN-1, a Novel Member of the Angiotensin-converting Enzyme Family That Lacks a Metallopeptidase Active Site

Genome sequence analyses predict many proteins that are structurally related to proteases but lack catalytic residues, thus making functional assignment difficult. We show that one of these proteins (ACN-1), a unique multi-domain angiotensin-converting enzyme (ACE)-like protein from Caenorhabditis elegans, is essential for larval development and adult morphogenesis. Green fluorescent protein-tagged ACN-1 is expressed in hypodermal cells, the developing vulva, and the ray papillae of the male tail. The hypodermal expression of acn-1 appears to be controlled by nhr-23 and nhr-25, two nuclear hormone receptors known to regulate molting in C. elegans. acn-1(RNAi) causes arrest of larval development because of a molting defect, a protruding vulva in adult hermaphrodites, severely disrupted alae, and an incomplete seam syncytium. Adult males also have multiple tail defects. The failure of the larval seam cells to undergo normal cell fusion is the likely reason for the severe disruption of the adult alae. We propose that alteration of the ancestral ACE during evolution, by loss of the metallopeptidase active site and the addition of new protein modules, has provided opportunities for novel molecular interactions important for post-embryonic development in nematodes.