Abelson tyrosine-protein kinase 2 regulates myoblast proliferation and controls muscle fiber length

Identification of IGF2BP1-related lncRNA-miRNA-mRNA network in goat skeletal muscle satellite cells

Insulin-like growth factor 2 mRNA-binding protein 1 (IGF2BP1) plays essential roles in the proliferation of skeletal muscle satellite cells (MuSCs). Increasing evidence has shown that IGF2BP1 regulates the expression of noncoding RNAs and mRNAs. However, the related molecular network remains to be fully understood. Therefore, we performed RNA sequencing and analyzed the microRNAs (miRNAs), long noncoding RNAs (lncRNAs), and mRNAs differentially expressed in goat MuSCs treated with IGF2BP1 overexpressing and empty vectors. A total of 36 miRNAs, 59 lncRNAs, and 44 mRNAs were differentially expressed caused by IGF2BP1. Expectedly, they were enriched in muscle development-related Rap1, PI3K-AKT, and FoxO signaling pathways. Finally, we constructed a lncRNA-miRNA-mRNA interaction network containing 30 lncRNAs, 15 miRNAs, and 34 mRNAs, in which several miRNAs, including miR-133a-3p, miR-204-5p, miR-125a-3p, miR-145-3p, and miR-423-5p, relate with cell growth and participate in muscle development. Overall, we constructed an IGF2BP1-related network, which provides new insight into the myogenic proliferation of goat.

Genome-wide association studies demonstrate that TASP1 contributes to increased muscle fiber diameter

Muscle fiber diameter is an economically important trait because it affects meat yield and quality. However, the genetic basis underlying muscle fiber diameter has not been determined. In this study, we collected THREE muscular histological phenotypes in 479 ducks from an F₂ segregating population generated by mallard × Pekin duck crosses. We performed genome-wide association studies (GWAS) and identified a quantitative trait locus (QTL) significantly associated with muscle fiber diameter on chromosome 3. Then, we discovered the selection signatures using the fixation index among 40 mallards and 30 Pekin ducks in this QTL region. Furthermore, we characterized the recombination event in this QTL region and identified a 6-kb block located on TASP1 that was significantly associated with muscle fiber diameter. Finally, five SNPs were screened as potential causative mutations within the 6-kb block. In conclusion, we demonstrated that TASP1 contributes to an increase in muscle fiber diameter, which helps to characterize muscle development and contributes to the genetic improvement of meat yield and quality in livestock.

c-Abl Kinase Is Required for Satellite Cell Function Through Pax7 Regulation

Satellite cells (SCs) are tissue-specific stem cells responsible for adult skeletal muscle regeneration and maintenance. SCs function is critically dependent on two families of transcription factors: the paired box (Pax) involved in specification and maintenance and the Muscle Regulatory Factors (MRFs), which orchestrate myogenic commitment and differentiation. In turn, signaling events triggered by extrinsic and intrinsic stimuli control their function via post-translational modifications, including ubiquitination and phosphorylation. In this context, the Abelson non-receptor tyrosine kinase (c-Abl) mediates the activation of the p38 α/β MAPK pathway, promoting myogenesis. c-Abl also regulates the activity of the transcription factor MyoD during DNA-damage stress response, pausing differentiation. However, it is not clear if c-Abl modulates other key transcription factors controlling SC function. This work aims to determine the role of c-Abl in SCs myogenic capacity via loss of function approaches in vitro and in vivo. Here we show that c-Abl inhibition or deletion results in a down-regulation of Pax7 mRNA and protein levels, accompanied by decreased Pax7 transcriptional activity, without a significant effect on MRF expression. Additionally, we provide data indicating that Pax7 is directly phosphorylated by c-Abl. Finally, SC-specific c-Abl ablation impairs muscle regeneration upon acute injury. Our results indicate that c-Abl regulates myogenic progression in activated SCs by controlling Pax7 function and expression.

Abelson kinase's intrinsically disordered region plays essential roles in protein function and protein stability

Background

The non-receptor tyrosine kinase Abelson (Abl) is a key player in oncogenesis, with kinase inhibitors serving as paradigms of targeted therapy. Abl also is a critical regulator of normal development, playing conserved roles in regulating cell behavior, brain development and morphogenesis. Drosophila offers a superb model for studying Abl’s normal function, because, unlike mammals, there is only a single fly Abl family member. In exploring the mechanism of action of multi-domain scaffolding proteins like Abl, one route is to define the roles of their individual domains. Research into Abl’s diverse roles in embryonic morphogenesis revealed many surprises. For instance, kinase activity, while important, is not crucial for all Abl activities, and the C-terminal F-actin binding domain plays a very modest role. This turned our attention to one of Abl’s least understood features—the long intrinsically-disordered region (IDR) linking Abl’s kinase and F-actin binding domains. The past decade revealed unexpected, important roles for IDRs in diverse cell functions, as sites of posttranslational modifications, mediating multivalent interactions and enabling assembly of biomolecular condensates via phase separation. Previous work deleting conserved regions in Abl’s IDR revealed an important role for a PXXP motif, but did not identify any other essential regions.

Methods

Here we extend this analysis by deleting the entire IDR, and asking whether Abl∆IDR rescues the diverse roles of Abl in viability and embryonic morphogenesis in Drosophila.

Results

This revealed that the IDR is essential for embryonic and adult viability, and for cell shape changes and cytoskeletal regulation during embryonic morphogenesis, and, most surprisingly, revealed a role in modulating protein stability.

Conclusion

Our data provide new insights into the role of the IDR in an important signaling protein, the non-receptor kinase Abl, suggesting that it is essential for all aspects of protein function during embryogenesis, and revealing a role in protein stability. These data will stimulate new explorations of the mechanisms by which the IDR regulates Abl stability and function, both in Drosophila and also in mammals. They also will stimulate further interest in the broader roles IDRs play in diverse signaling proteins.

Cancer-Induced Muscle Wasting Requires p38β MAPK Activation of p300

Cancer-associated cachexia, characterized by muscle wasting, is a lethal metabolic syndrome without defined etiology or established treatment. We previously found that p300 mediates cancer-induced muscle wasting by activating C/EBPβ, which then upregulates key catabolic genes. However, the signaling mechanism that activates p300 in response to cancer is unknown. Here, we show that upon cancer-induced activation of Toll-like receptor 4 in skeletal muscle, p38β MAPK phosphorylates Ser-12 on p300 to stimulate C/EBPβ acetylation, which is necessary and sufficient to cause muscle wasting. Thus, p38β MAPK is a central mediator and therapeutic target of cancer-induced muscle wasting. In addition, nilotinib, an FDA-approved kinase inhibitor that preferentially binds p38β MAPK, inhibited p300 activation 20-fold more potently than the p38α/β MAPK inhibitor, SB202190, and abrogated cancer cell-induced muscle protein loss in C2C12 myotubes without suppressing p38α MAPK-dependent myogenesis. Systemic administration of nilotinib at a low dose (0.5 mg/kg/day, i.p.) in tumor-bearing mice not only alleviated muscle wasting, but also prolonged survival. Therefore, nilotinib appears to be a promising treatment for human cancer cachexia due to its selective inhibition of p38β MAPK. SIGNIFICANCE: These findings demonstrate that prevention of p38β MAPK-mediated activation of p300 by the FDA-approved kinase inhibitor, nilotinib, ameliorates cancer cachexia, representing a potential therapeutic strategy against this syndrome.

Myogenesis control by SIX transcriptional complexes

SIX homeoproteins were first described in Drosophila, where they participate in the Pax-Six-Eya-Dach (PSED) network with eyeless, eyes absent and dachsund to drive synergistically eye development through genetic and biochemical interactions. The role of the PSED network and SIX proteins in muscle formation in vertebrates was subsequently identified. Evolutionary conserved interactions with EYA and DACH proteins underlie the activity of SIX transcriptional complexes (STC) both during embryogenesis and in adult myofibers. Six genes are expressed throughout muscle development, in embryonic and adult proliferating myogenic stem cells and in fetal and adult post-mitotic myofibers, where SIX proteins regulate the expression of various categories of genes. In vivo, SIX proteins control many steps of muscle development, acting through feedforward mechanisms: in the embryo for myogenic fate acquisition through the direct control of Myogenic Regulatory Factors; in adult myofibers for their contraction/relaxation and fatigability properties through the control of genes involved in metabolism, sarcomeric organization and calcium homeostasis. Furthermore, during development and in the adult, SIX homeoproteins participate in the genesis and the maintenance of myofibers diversity.

ABL kinase inhibition promotes lung regeneration through expansion of an SCGB1A1+ SPC+ cell population following bacterial pneumonia

Current therapeutic interventions for the treatment of respiratory infections are hampered by the evolution of multidrug resistance in pathogens as well as the lack of effective cellular targets. Despite the identification of multiple region-specific lung progenitor cells, the identity of molecules that might be therapeutically targeted in response to infections to promote activation of progenitor cell types remains elusive. Here, we report that loss of Abl1 specifically in SCGB1A1-expressing cells leads to a significant increase in the proliferation and differentiation of bronchiolar epithelial cells, resulting in dramatic expansion of an SCGB1A1+ airway cell population that coexpresses SPC, a marker for type II alveolar cells that promotes alveolar regeneration following bacterial pneumonia. Furthermore, treatment with an Abl-specific allosteric inhibitor enhanced regeneration of the alveolar epithelium and promoted accelerated recovery of mice following pneumonia. These data reveal a potential actionable target that may be exploited for efficient recovery after pathogen-induced infections.

Developmental origin and morphogenesis of the diaphragm, an essential mammalian muscle

The diaphragm is a mammalian skeletal muscle essential for respiration and for separating the thoracic and abdominal cavities. Development of the diaphragm requires the coordinated development of muscle, muscle connective tissue, tendon, nerves, and vasculature that derive from different embryonic sources. However, defects in diaphragm development are common and the cause of an often deadly birth defect, Congenital Diaphragmatic Hernia (CDH). Here we comprehensively describe the normal developmental origin and complex spatial-temporal relationship between the different developing tissues to form a functional diaphragm using a developmental series of mouse embryos genetically and immunofluorescently labeled and analyzed in whole mount. We find that the earliest developmental events are the emigration of muscle progenitors from cervical somites followed by the projection of phrenic nerve axons from the cervical neural tube. Muscle progenitors and phrenic nerve target the pleuroperitoneal folds (PPFs), transient pyramidal-shaped structures that form between the thoracic and abdominal cavities. Subsequently, the PPFs expand across the surface of the liver to give rise to the muscle connective tissue and central tendon, and the leading edge of their expansion precedes muscle morphogenesis, formation of the vascular network, and outgrowth and branching of the phrenic nerve. Thus development and morphogenesis of the PPFs is critical for diaphragm formation. In addition, our data indicate that the earliest events in diaphragm development are critical for the etiology of CDH and instrumental to the evolution of the diaphragm. CDH initiates prior to E12.5 in mouse and suggests that defects in the early PPF formation or their ability to recruit muscle are an important source of CDH. Also, the recruitment of muscle progenitors from cervical somites to the nascent PPFs is uniquely mammalian and a key developmental innovation essential for the evolution of the muscularized diaphragm.