BCL9 is an essential component of canonical Wnt signaling that mediates the differentiation of myogenic progenitors during muscle regeneration

Delta-like noncanonical notch ligand 2 regulates the proliferation and differentiation of sheep myoblasts through the Wnt/β-catenin signaling pathway

This study delved into the role of delta-like noncanonical notch ligand 2 (DLK2) in the cell cycle, proliferation, apoptosis, and differentiation of myoblasts, as well as its interaction with the classical Wnt/β-catenin signaling pathway in regulating myoblast function. The research revealed that upregulation of DLK2 in myoblasts during the proliferation phase enhanced myoblast proliferation, facilitated cell cycle progression, and reduced apoptosis. Conversely, downregulation of DLK2 expression using siRNA during the differentiation phase promoted myoblast hypertrophy and fusion, suppressed the expression of muscle fiber degradation factors, and expedited the differentiation process. DLK2 regulates myoblasts function by influencing the expression of various factors associated with the Wnt/β-catenin signaling pathway, including CTNNB1, FZD1, FZD6, RSPO1, RSPO4, WNT4, WNT5A, and adenomatous polyposis coli. In essence, DLK2, with the involvement of the Wnt/β-catenin signaling pathway, plays a crucial regulatory role in the cell cycle, proliferation, apoptosis, and differentiation of myoblasts.

LSD1 controls a nuclear checkpoint in Wnt/β-Catenin signaling to regulate muscle stem cell self-renewal

The Wnt/β-Catenin pathway plays a key role in cell fate determination during development and in adult tissue regeneration by stem cells. These processes involve profound gene expression and epigenome remodeling and linking Wnt/β-Catenin signaling to chromatin modifications has been a challenge over the past decades. Functional studies of the lysine demethylase LSD1/KDM1A converge to indicate that this epigenetic regulator is a key regulator of cell fate, although the extracellular cues controlling LSD1 action remain largely unknown. Here we show that β-Catenin is a substrate of LSD1. Demethylation by LSD1 prevents β-Catenin degradation thereby maintaining its nuclear levels. Consistently, in absence of LSD1, β-Catenin transcriptional activity is reduced in both MuSCs and ESCs. Moreover, inactivation of LSD1 in mouse muscle stem cells and embryonic stem cells shows that LSD1 promotes mitotic spindle orientation via β-Catenin protein stabilization. Altogether, by inscribing LSD1 and β-Catenin in the same molecular cascade linking extracellular factors to gene expression, our results provide a mechanistic explanation to the similarity of action of canonical Wnt/β-Catenin signaling and LSD1 on stem cell fate.

Long non-coding RNAs and their role in muscle regeneration

In mammals, most of the genome is transcribed to generate a large and heterogeneous variety of non-protein coding RNAs, that are broadly grouped according to their size. Long noncoding RNAs include a very large and versatile group of molecules. Despite only a minority of them has been functionally characterized, there is emerging evidence indicating long noncoding RNAs as important regulators of expression at multiple levels. Several of them have been shown to be modulated during myogenic differentiation, playing important roles in the regulation of skeletal muscle development, differentiation and homeostasis, and contributing to neuromuscular diseases. In this chapter, we have summarized the current knowledge about long noncoding RNAs in skeletal muscle and discussed specific examples of long noncoding RNAs (lncRNAs and circRNAs) regulating muscle stem cell biology. We have also discussed selected long noncoding RNAs involved in the most common neuromuscular diseases.

Native collagen VI delays early muscle stem cell differentiation

Adult muscle stem cells (MuSCs) are critical for muscle homeostasis and regeneration, and their behavior relies on a finely regulated niche made of specific extracellular matrix (ECM) components and soluble factors. Among ECM proteins, collagen VI (Col6) influences the mechanical properties of the niche and, in turn, MuSC self-renewal capabilities. Here, we investigated whether Col6 can exert a direct function as a biochemical signal for regulating the stemness and differentiation of murine MuSCs and myoblasts. Native Col6, but not its pepsin-resistant fragment, counteracts the early differentiation of myogenic cells by reducing the expression of differentiation marker genes and preserving stemness features, with inhibition of the canonical Wnt pathway. Our data indicate that extracellular Col6 acts as a soluble ligand in delaying early myogenic differentiation by regulating intracellular signals involved in adult myogenesis.

Genomic inbreeding estimation, runs of homozygosity, and heterozygosity-enriched regions uncover signals of selection in the Quarter Horse racing line

With the advent of genomics, significant progress has been made in the genetic improvement of livestock species, particularly through increased accuracy in predicting breeding values for selecting superior animals and the possibility of performing a high-resolution genetic scan throughout the genome of an individual. The main objectives of this study were to estimate the individual genomic inbreeding coefficient based on runs of homozygosity (FROH ), to identify and characterize runs of homozygosity and heterozygosity (ROH and ROHet, respectively; length and distribution) throughout the genome, and to map selection signatures in relevant chromosomal regions in the Quarter Horse racing line. A total of 336 animals registered with the Brazilian Association of Quarter Horse Breeders (ABQM) were genotyped. One hundred and twelve animals were genotyped using the Equine SNP50 BeadChip (Illumina, USA), with 54,602 single nucleotide polymorphisms (SNPs; 54K). The remaining 224 samples were genotyped using the Equine SNP70 BeadChip (Illumina, USA) with 65,157 SNPs (65K). To ensure data quality, we excluded animals with a call rate below 0.9. We also excluded SNPs located on non-autosomal chromosomes, as well as those with a call rate below 0.9 or a p-value below 1 × 10-5 for Hardy-Weinberg equilibrium. The results indicate moderate to high genomic inbreeding, with 46,594 ROH and 16,101 ROHet detected. In total, 30 and 14 candidate genes overlap with ROH and ROHet regions, respectively. The ROH islands showed genes linked to crucial biological processes, such as cell differentiation (CTBP1, WNT5B, and TMEM120B), regulation of glucose metabolic process (MAEA and NKX1-1), heme transport (PGRMC2), and negative regulation of calcium ion import (VDAC1). In ROHet, the islands showed genes related to respiratory capacity (OR7D19, OR7D4G, OR7D4E, and OR7D4J) and muscle repair (EGFR and BCL9). These findings could aid in selecting animals with greater regenerative capacity and developing treatments for muscle disorders in the QH breed. This study serves as a foundation for future research on equine breeds. It can contribute to developing reproductive strategies in animal breeding programs to improve and preserve the Quarter Horse breed.

Axonal Regeneration: Underlying Molecular Mechanisms and Potential Therapeutic Targets

Axons in the peripheral nervous system have the ability to repair themselves after damage, whereas axons in the central nervous system are unable to do so. A common and important characteristic of damage to the spinal cord, brain, and peripheral nerves is the disruption of axonal regrowth. Interestingly, intrinsic growth factors play a significant role in the axonal regeneration of injured nerves. Various factors such as proteomic profile, microtubule stability, ribosomal location, and signalling pathways mark a line between the central and peripheral axons' capacity for self-renewal. Unfortunately, glial scar development, myelin-associated inhibitor molecules, lack of neurotrophic factors, and inflammatory reactions are among the factors that restrict axonal regeneration. Molecular pathways such as cAMP, MAPK, JAK/STAT, ATF3/CREB, BMP/SMAD, AKT/mTORC1/p70S6K, PI3K/AKT, GSK-3β/CLASP, BDNF/Trk, Ras/ERK, integrin/FAK, RhoA/ROCK/LIMK, and POSTN/integrin are activated after nerve injury and are considered significant players in axonal regeneration. In addition to the aforementioned pathways, growth factors, microRNAs, and astrocytes are also commendable participants in regeneration. In this review, we discuss the detailed mechanism of each pathway along with key players that can be potentially valuable targets to help achieve quick axonal healing. We also identify the prospective targets that could help close knowledge gaps in the molecular pathways underlying regeneration and shed light on the creation of more powerful strategies to encourage axonal regeneration after nervous system injury.

Emerging Direct Targeting β-Catenin Agents

Aberrant accumulation of β-catenin in the cell nucleus as a result of deregulation of the Wnt/β-catenin pathway is found in various types of cancer. Direct β-catenin targeting agents are being researched despite obstacles; however, specific β-catenin drugs for clinical treatments have not been approved so far. We focused on direct β-catenin targeting of potential therapeutic value as anticancer agents. This review provides recent advances on small molecule β-catenin agents. Structure-activity relationships and biological activities of reported inhibitors are discussed. This work provides useful knowledge in the discovery of β-catenin agents.

Hypoxia-inducible factor 1α induces osteo/odontoblast differentiation of human dental pulp stem cells via Wnt/β-catenin transcriptional cofactor BCL9

Accelerated dental pulp mineralization is a common complication in avulsed/luxated teeth, although the mechanisms underlying this remain unclear. We hypothesized that hypoxia due to vascular severance may induce osteo/odontoblast differentiation of dental pulp stem cells (DPSCs). This study examined the role of B-cell CLL/lymphoma 9 (BCL9), which is downstream of hypoxia-inducible factor 1α (HIF1α) and a Wnt/β-catenin transcriptional cofactor, in the osteo/odontoblastic differentiation of human DPSCs (hDPSCs) under hypoxic conditions. hDPSCs were isolated from extracted healthy wisdom teeth. Hypoxic conditions and HIF1α overexpression induced significant upregulation of mRNAs for osteo/odontoblast markers (RUNX2, ALP, OC), BCL9, and Wnt/β-catenin signaling target genes (AXIN2, TCF1) in hDPSCs. Overexpression and suppression of BCL9 in hDPSCs up- and downregulated, respectively, the mRNAs for AXIN2, TCF1, and the osteo/odontoblast markers. Hypoxic-cultured mouse pulp tissue explants showed the promotion of HIF1α, BCL9, and β-catenin expression and BCL9-β-catenin co-localization. In addition, BCL9 formed a complex with β-catenin in hDPSCs in vitro. This study demonstrated that hypoxia/HIF1α-induced osteo/odontoblast differentiation of hDPSCs was partially dependent on Wnt/β-catenin signaling, where BCL9 acted as a key mediator between HIF1α and Wnt/β-catenin signaling. These findings may reveal part of the mechanisms of dental pulp mineralization after traumatic dental injury.

Circular RNA circFNDC3AL Upregulates BCL9 Expression to Promote Chicken Skeletal Muscle Satellite Cells Proliferation and Differentiation by Binding to miR-204

Skeletal muscle is a heterogeneous tissue that is essential for initiating movement and maintaining homeostasis. The genesis of skeletal muscle is an integrative process that lasts from embryonic development to postnatal stages, which is carried out under the modulation of many factors. Recent studies have shown that circular RNAs (circRNAs), a class of non-coding RNAs, are involved in myogenesis. However, more circRNAs and their mechanisms that may regulate skeletal muscle development remain to be explored. Through in-depth analysis of our previous RNA-Seq data, circFNDC3AL was found to be a potentially functional circRNA highly expressed during embryonic development of chicken skeletal muscle. Therefore, in this study, we investigated the effect of circFNDC3AL on skeletal muscle development in chickens and found that circFNDC3AL promoted chicken skeletal muscle satellite cell (SMSC) proliferation and differentiation. To gain a thorough understanding of the exact modulatory mechanisms of circFNDC3AL in chicken skeletal muscle development, we performed target miRNA analysis of circFNDC3AL and found that circFNDC3AL has a binding site for miR-204. Subsequently, we demonstrated that miR-204 inhibited chicken SMSC proliferation and differentiation, which showed the opposite functions of circFNDC3AL. Furthermore, we identified the miR-204 target gene B-cell CLL/lymphoma 9 (BCL9) and validated that miR-204 had an inhibitory effect on BCL9, while the negative effect could be relieved by circFNDC3AL. In addition, we verified that BCL9 performed the same positive functions on chicken SMSC proliferation and differentiation as circFNDC3AL, as opposed to miR-204. In conclusion, our study identified a circRNA circFNDC3AL that upregulates BCL9 expression to promote the proliferation and differentiation of chicken SMSCs by binding to miR-204.

Dissecting Molecular Genetic Mechanisms of 1q21.1 CNV in Neuropsychiatric Disorders

Pathogenic copy number variations (CNVs) contribute to the etiology of neurodevelopmental/neuropsychiatric disorders (NDs). Increased CNV burden has been found to be critically involved in NDs compared with controls in clinical studies. The 1q21.1 CNVs, rare and large chromosomal microduplications and microdeletions, are detected in many patients with NDs. Phenotypes of duplication and deletion appear at the two ends of the spectrum. Microdeletions are predominant in individuals with schizophrenia (SCZ) and microcephaly, whereas microduplications are predominant in individuals with autism spectrum disorder (ASD) and macrocephaly. However, its complexity hinders the discovery of molecular pathways and phenotypic networks. In this review, we summarize the recent genome-wide association studies (GWASs) that have identified candidate genes positively correlated with 1q21.1 CNVs, which are likely to contribute to abnormal phenotypes in carriers. We discuss the clinical data implicated in the 1q21.1 genetic structure that is strongly associated with neurodevelopmental dysfunctions like cognitive impairment and reduced synaptic plasticity. We further present variations reported in the phenotypic severity, genomic penetrance and inheritance.

Function of the Porcine TRPC1 Gene in Myogenesis and Muscle Growth

In animals, muscle growth is a quantitative trait controlled by multiple genes. Previously, we showed that the transient receptor potential channel 1 (TRPC1) gene was differentially expressed in muscle tissues between pig breeds with divergent growth traits base on RNA-seq. Here, we characterized TRPC1 expression profiles in different tissues and pig breeds and showed that TRPC1 was highly expressed in the muscle. We found two single nucleotide polymorphisms (SNPs) (C-1763T and C-1604T) in TRPC1 that could affect the promoter region activity and regulate pig growth rate. Functionally, we used RNAi and overexpression to illustrate that TRPC1 promotes myoblast proliferation, migration, differentiation, fusion, and muscle hypertrophy while inhibiting muscle degradation. These processes may be mediated by the activation of Wnt signaling pathways. Altogether, our results revealed that TRPC1 might promote muscle growth and development and plays a key role in Wnt-mediated myogenesis.

RNA-Seq Reveals miRNA Role Shifts in Seven Stages of Skeletal Muscles in Goat Fetuses and Kids

MicroRNAs (miRNAs) are indispensable for the regulation of skeletal muscle. We performed RNA sequencing (RNA-seq) to establish a comprehensive miRNA profiling of goats in seven stages, namely, 45- (F45), 65- (F65), 90- (F90), 120- (F120), and 135-day (F135) fetuses, newborn (B1), and 90-day-old (B90) kids. In total, 421 known miRNAs and 228 goat novel miRNAs were identified in the data, and the average abundance of 19 miRNAs in seven stages exceeds 10,000 reads per million. Furthermore, 420 differentially expressed miRNAs (DEmiRNAs) were identified in all comparison group at seven stages, 80 of which were uniquely differentially expressed in the B1 and B90 comparison groups. Pathway analysis indicated that this group was associated with the release of muscle hypertrophy and regulation of myoblast proliferation. Besides, 305 DEmiRNAs were clustered into three significantly enriched profiles (profiles 11, 16, and 19). Function analysis revealed that profile 16 was related to muscle hypertrophy and differentiation. Profile 11 was involved in multiple enzyme activities and metabolic processes in muscle cells. And profile 19 was involved in material transport and structural stability. Two highly expressed miRNAs and three key miRNAs (chi-miR-328-3p, chi-miR-767, and chi-miR-150) of these profiles were verified to be consistent with the data by quantitative real-time PCR. These results provided a catalog of goat muscle-associated miRNAs, allowing us to better understand the transformation of miRNA roles during mammalian muscle development.

Traction and attraction: haptotaxis substrates collagen and fibronectin interact with chemotaxis by HGF to regulate myoblast migration in a microfluidic device

Cell migration is central to development, wound healing, tissue regeneration, and immunity. Despite extensive knowledge of muscle regeneration, myoblast migration during regeneration is not well understood. C2C12 mouse myoblast migration and morphology were investigated using a triple-docking polydimethylsiloxane-based microfluidic device in which cells moved under gravity-driven laminar flow on uniform (=) collagen (CN=), fibronectin (FN=), or opposing gradients (CN-FN or FN-CN). In haptotaxis experiments, migration was faster on FN= than on CN=. At 10 h, cells were more elongated on FN-CN and migration was faster than on the CN-FN substrate. Net migration distance on FN-CN at 10 h was greater than on CN-FN, as cells rapidly entered the channel as a larger population (bulk-cell movement, wave 1). Hepatocyte growth factor (HGF) stimulated rapid chemotaxis on FN= but not CN=, increasing migration speed at 10 h early in the channel at low HGF in a steep HGF gradient. HGF accelerated migration on FN= and bulk-cell movement on both uniform substrates. An HGF gradient also slowed cells in wave 2 moving on FN-CN, not CN-FN. Both opposing-gradient substrates affected the shape, speed, and net distance of migrating cells. Gradient and uniform configurations of HGF and substrate differentially influenced migration behavior. Therefore, haptotaxis substrate configuration potently modifies myoblast chemotaxis by HGF. Innovative microfluidic experiments advance our understanding of intricate complexities of myoblast migration. Findings can be leveraged to engineer muscle-tissue volumes for transplantation after serious injury. New analytical approaches may generate broader insights into cell migration.

Ectonucleotide pyrophosphatase 2 (ENPP2) plays a crucial role in myogenic differentiation through the regulation by WNT/β-Catenin signaling

Ectonucleotide pyrophosphate phosphodiesterase type II (ENPP2), also known as Autotaxin (ATX), is an enzyme present in blood circulation that converts lysophosphatidyl choline (LPC) to lysophosphatidic acid (LPA). While LPA has been demonstrated to play diverse roles in skeletal myogenesis, mainly through in vitro studies, the role of ENPP2 in skeletal myogenesis has not been determined. We previously found that Enpp2 is induced by a positive WNT/β-Catenin signaling regulator, R-spondin2 (RSPO2), in C2C12 myoblast cells. As RSPO2 promotes myogenic differentiation via the WNT/β-Catenin signaling pathway, we hypothesized that ENPP2 may act as a key mediator for the crosstalk between WNT and LPA signaling during myogenic differentiation. Herein, we found that ENPP2 function is essential for myogenic differentiation in C2C12 cells. Pharmacological ENPP2 inhibitors or RNAi-mediated Enpp2 gene knockdown severely impaired the myogenic differentiation, including the cell fusion process, whereas administration of the recombinant ENPP2 protein enhanced myogenic differentiation. Consistent with the in vitro results, mice lacking the Enpp2 gene showed a disrupted muscle regeneration after acute muscle injury. The size of newly regenerated myofibers in Enpp2 mutant muscle was significantly reduced compared with wild-type regenerated muscle. Modified expression patterns of myogenic markers in Enpp2 mutant muscle further emphasized the impaired muscle regeneration process. Finally, we convincingly demonstrate that the Enpp2 gene is a direct transcriptional target for WNT/β-Catenin signaling. Functional TCF/LEF1 binding sites within the upstream region of Enpp2 gene were identified by chromatin immunoprecipitation using anti-β-Catenin antibodies and reporter assay. Our study reveals that ENPP2 is regulated by WNT/β-Catenin signaling and plays a key positive role in myogenic differentiation.

The effect of strength and endurance training on SSTR2 and SSTR5 in patients with colorectal cancer

The roots of apoptosis caused by the use of certain drugs in patients with colorectal cancer and certain drugs could be induced the change in genes SSTR2 and SSTR5. SSTRs play a role in colorectal cancer and it’s also known that exercise training has similar effects to certain drugs. Therefore, this study aims to evaluate the effects of a combined training program on hormonal and physiological changes in patients with colorectal cancer. Twenty patients with colorectal cancer were included in this study and divided into two groups as experimental (n=10) and control (n=10). The experimental group performed an exercise training program 5 days a week for 14 weeks. Blood samples were taken from the patients before and after the training program, and analyzed for somatostatin and its receptors. When the pretest effect excluded as statistical, there were no significant differences in SSRT2 (P>0.05) and SSRT5 (P>0.05) between the experimental and control groups. The hypothesis for this study was “SSTR2 and SSTR5 will improve after combined training program” however, in accordance with the results it was rejected. It seems that the determined training program for these patients need to be extended and performed for at least 3 months in a gradual incremental structure so that it could affect their health indicators significantly.

Wnt4 from the Niche Controls the Mechano-Properties and Quiescent State of Muscle Stem Cells

Satellite cells (SCs) reside in a dormant state during tissue homeostasis. The specific paracrine agents and niche cells that maintain SC quiescence remain unknown. We find that Wnt4 produced by the muscle fiber maintains SC quiescence through RhoA. Using cell-specific inducible genetics, we find that a Wnt4-Rho signaling axis constrains SC numbers and activation during tissue homeostasis in adult mice. Wnt4 activates Rho in quiescent SCs to maintain mechanical strain, restrict movement in the niche, and repress YAP. The induction of YAP upon disruption of RhoA is essential for SC activation under homeostasis. In the context of injury, the loss of Wnt4 from the niche accelerates SC activation and muscle repair, whereas overexpression of Wnt4 transitions SCs into a deeper state of quiescence and delays muscle repair. In conclusion, the SC pool undergoes dynamic transitions during early activation with changes in mechano-properties and cytoskeleton signaling preceding cell-cycle entry.

Wnt status-dependent oncogenic role of BCL9 and BCL9L in hepatocellular carcinoma

Background

Activation of Wnt/β-catenin pathway is a frequent event in hepatocellular carcinoma and is associated with enhanced cell survival and proliferation. Therefore, targeting this signaling pathway is discussed as an attractive therapeutic approach for HCC treatment. BCL9 and BCL9L, two homologous coactivators of the β-catenin transcription factor complex, have not yet been comprehensively characterized in HCC. We aimed to elucidate the roles of BCL9 and BCL9L, especially regarding Wnt/β-catenin signaling and their prognostic value in HCC.

Methods

Expression of BCL9/BCL9L was determined in HCC cell lines (HLE, HLF, Huh7, HepG2, Hep3B, and Huh6) and normal liver cell lines (THLE-2 and THLE-3). To analyze proliferation and apoptosis, BCL9 and/or BCL9L were knocked down in Wnt-inactive HLE and Wnt-active HepG2 and Huh6 cells using siRNA. Subsequently, Wnt reporter assays were performed in HepG2 and Huh6 cells. BCL9 and BCL9L expression, clinicopathological and survival data of public HCC datasets were analyzed, taking the Wnt signaling status into account.

Results

Knockdown of BCL9L, but not of BCL9, reduced Wnt signaling activity. Knockdown of BCL9 and/or BCL9L reduced cell viability and increased apoptosis of Wnt-inactive HCC cells, but had no effect in Wnt-active cells. Expression of BCL9 and BCL9L was upregulated in human HCC and increased with progressing dedifferentiation. For BCL9L, higher expression was observed in tumors of larger size. Overexpression of BCL9 and BCL9L correlated with poor overall survival, especially in HCC without activated Wnt signaling.

Conclusion

Oncogenic BCL9 proteins represent promising targets for cancer therapy and inhibiting them may be particularly beneficial in Wnt-inactive HCCs.

Graphic abstract

Electronic supplementary material

The online version of this article (10.1007/s12072-019-09977-w) contains supplementary material, which is available to authorized users.

Radicicol enhances the regeneration of skeletal muscle injured by crotoxin via decrease of NF-kB activation

This study evaluated cellular and molecular effects of radicicol, a heat shock protein (HSP) inducer, on the regeneration of skeletal muscle injured by crotoxin, the main toxin isolated from Crotalus durissus terrificus venom. Regenerating muscles treated with radicicol had decreased NF-kB activation. Differentiating myoblasts treated with radicicol showed reduced number of NF-kB positive nuclei and increased fusion index. The results suggest that radicicol enhances regeneration of muscle by attenuating NF-kB activation and increasing myogenic differentiation.

The Nuclear Receptor and Clock Repressor Rev-erbα Suppresses Myogenesis

Rev-erbα is a ligand-dependent nuclear receptor and a key repressor of the molecular clock transcription network. Accumulating evidence indicate that the circadian clock machinery governs diverse biological processes in skeletal muscle, including muscle growth, repair and mass maintenance. The physiological function of Rev-erbα in myogenic regulation remains largely unknown. Here we show that Rev-erbα exerts cell-autonomous inhibitory effects on proliferation and differentiation of myogenic precursor cells, and these actions concertedly inhibit muscle regeneration in vivo. Mechanistic studies reveal Rev-erbα direct transcriptional control of two major myogenic mechanisms, proliferative pathway and the Wnt signaling cascade. Consistent with this finding, primary myoblasts lacking Rev-erbα display significantly enhanced proliferative growth and myogenic progression. Furthermore, pharmacological activation of Rev-erbα activity attenuates, whereas its inhibition by an antagonist promotes these processes. Notably, upon muscle injury, the loss-of-function of Rev-erbα in vivo augmented satellite cell proliferative expansion and regenerative progression during regeneration. Collectively, our study identifies Rev-erbα as a novel inhibitory regulator of myogenic progenitor cell properties that suppresses postnatal myogenesis. Pharmacological interventions to dampen Rev-erbα activity may have potential utilities to enhance regenerative capacity in muscle diseases.

Bcl9 and Pygo synergise downstream of Apc to effect intestinal neoplasia in FAP mouse models

Bcl9 and Pygo are Wnt enhanceosome components that effect β-catenin-dependent transcription. Whether they mediate β-catenin-dependent neoplasia is unclear. Here we assess their roles in intestinal tumourigenesis initiated by Apc loss-of-function (ApcMin), or by Apc1322T encoding a partially-functional Apc truncation commonly found in colorectal carcinomas. Intestinal deletion of Bcl9 extends disease-free survival in both models, and essentially cures Apc1322T mice of their neoplasia. Loss-of-Bcl9 synergises with loss-of-Pygo to shift gene expression within Apc-mutant adenomas from stem cell-like to differentiation along Notch-regulated secretory lineages. Bcl9 loss also promotes tumour retention in ApcMin mice, apparently via relocating nuclear β-catenin to the cell surface, but this undesirable effect is not seen in Apc1322T mice whose Apc truncation retains partial function in regulating β-catenin. Our results demonstrate a key role of the Wnt enhanceosome in β-catenin-dependent intestinal tumourigenesis and reveal the potential of BCL9 as a therapeutic target during early stages of colorectal cancer.

Loss of BCL9/9l suppresses Wnt driven tumourigenesis in models that recapitulate human cancer

Different thresholds of Wnt signalling are thought to drive stem cell maintenance, regeneration, differentiation and cancer. However, the principle that oncogenic Wnt signalling could be specifically targeted remains controversial. Here we examine the requirement of BCL9/9l, constituents of the Wnt-enhanceosome, for intestinal transformation following loss of the tumour suppressor APC. Although required for Lgr5+ intestinal stem cells and regeneration, Bcl9/9l deletion has no impact upon normal intestinal homeostasis. Loss of BCL9/9l suppressed many features of acute APC loss and subsequent Wnt pathway deregulation in vivo. This resulted in a level of Wnt pathway activation that favoured tumour initiation in the proximal small intestine (SI) and blocked tumour growth in the colon. Furthermore, Bcl9/9l deletion completely abrogated β-catenin driven intestinal and hepatocellular transformation. We speculate these results support the just-right hypothesis of Wnt-driven tumour formation. Importantly, loss of BCL9/9l is particularly effective at blocking colonic tumourigenesis and mutations that most resemble those that occur in human cancer.

Islr regulates canonical Wnt signaling-mediated skeletal muscle regeneration by stabilizing Dishevelled-2 and preventing autophagy

Satellite cells are crucial for skeletal muscle regeneration, but the molecular mechanisms regulating satellite cells are not entirely understood. Here, we show that the immunoglobulin superfamily containing leucine-rich repeat (Islr), a newly identified marker for mesenchymal stem cells, stabilizes canonical Wnt signaling and promote skeletal muscle regeneration. Loss of Islr delays skeletal muscle regeneration in adult mice. In the absence of Islr, myoblasts fail to develop into mature myotubes due to defective differentiation. Islr interacts with Dishevelled-2 (Dvl2) to activate canonical Wnt signaling, consequently regulating the myogenic factor myogenin (MyoG). Furthermore, Islr stabilizes Dvl2 by reducing the level of LC3-labeled Dvl2 and preventing cells from undergoing autophagy. Together, our findings identify Islr as an important regulator for skeletal muscle regeneration.

“Satellite cells are crucial for skeletal muscle regeneration. Here the authors show that immunoglobulin superfamily containing leucine-rich repeat (Islr) promotes skeletal muscle regeneration via a mechanism involving Dishevelled-2 stabilization in satellite cells and protection from autophagy.

GSK3β inhibitor promotes myelination and mitigates muscle atrophy after peripheral nerve injury

Delay of axon regeneration after peripheral nerve injury usually leads to progressive muscle atrophy and poor functional recovery. The Wnt/β-catenin signaling pathway is considered to be one of the main molecular mechanisms that lead to skeletal muscle atrophy in the elderly. We hold the hypothesis that the innervation of target muscle can be promoted by accelerating axon regeneration and decelerating muscle cell degeneration so as to improve functional recovery of skeletal muscle following peripheral nerve injury. This process may be associated with the Wnt/β-catenin signaling pathway. Our study designed in vitro cell models to simulate myelin regeneration and muscle atrophy. We investigated the effects of SB216763, a glycogen synthase kinase 3 beta inhibitor, on the two major murine cell lines RSC96 and C2C12 derived from Schwann cells and muscle satellite cells. The results showed that SB216763 stimulated the Schwann cell migration and myotube contraction. Quantitative polymerase chain reaction results demonstrated that myelin related genes, myelin associated glycoprotein and cyclin-D1, muscle related gene myogenin and endplate-associated gene nicotinic acetylcholine receptors levels were stimulated by SB216763. Immunocytochemical staining revealed that the expressions of β-catenin in the RSC96 and C2C12 cytosolic and nuclear compartments were increased in the SB216763-treated cells. These findings confirm that the glycogen synthase kinase 3 beta inhibitor, SB216763, promoted the myelination and myotube differentiation through the Wnt/β-catenin signaling pathway and contributed to nerve remyelination and reduced denervated muscle atrophy after peripheral nerve injury.

Inhibition of Methyltransferase Setd7 Allows the In Vitro Expansion of Myogenic Stem Cells with Improved Therapeutic Potential

The development of cell therapy for repairing damaged or diseased skeletal muscle has been hindered by the inability to significantly expand immature, transplantable myogenic stem cells (MuSCs) in culture. To overcome this limitation, a deeper understanding of the mechanisms regulating the transition between activated, proliferating MuSCs and differentiation-primed, poorly engrafting progenitors is needed. Here, we show that methyltransferase Setd7 facilitates such transition by regulating the nuclear accumulation of β-catenin in proliferating MuSCs. Genetic or pharmacological inhibition of Setd7 promotes in vitro expansion of MuSCs and increases the yield of primary myogenic cell cultures. Upon transplantation, both mouse and human MuSCs expanded with a Setd7 small-molecule inhibitor are better able to repopulate the satellite cell niche, and treated mouse MuSCs show enhanced therapeutic potential in preclinical models of muscular dystrophy. Thus, Setd7 inhibition may help bypass a key obstacle in the translation of cell therapy for muscle disease.

Identification of satellite cells from anole lizard skeletal muscle and demonstration of expanded musculoskeletal potential

The lizards are evolutionarily the closest vertebrates to humans that demonstrate the ability to regenerate entire appendages containing cartilage, muscle, skin, and nervous tissue. We previously isolated PAX7-positive cells from muscle of the green anole lizard, Anolis carolinensis, that can differentiate into multinucleated myotubes and express the muscle structural protein, myosin heavy chain. Studying gene expression in these satellite/progenitor cell populations from A. carolinensis can provide insight into the mechanisms regulating tissue regeneration. We generated a transcriptome from proliferating lizard myoprogenitor cells and compared them to transcriptomes from the mouse and human tissues from the ENCODE project using XGSA, a statistical method for cross-species gene set analysis. These analyses determined that the lizard progenitor cell transcriptome was most similar to mammalian satellite cells. Further examination of specific GO categories of genes demonstrated that among genes with the highest level of expression in lizard satellite cells were an increased number of genetic regulators of chondrogenesis, as compared to mouse satellite cells. In micromass culture, lizard PAX7-positive cells formed Alcian blue and collagen 2a1 positive nodules, without the addition of exogenous morphogens, unlike their mouse counterparts. Subsequent quantitative RT-PCR confirmed up-regulation of expression of chondrogenic regulatory genes in lizard cells, including bmp2, sox9, runx2, and cartilage specific structural genes, aggrecan and collagen 2a1. Taken together, these data suggest that tail regeneration in lizards involves significant alterations in gene regulation with expanded musculoskeletal potency.

R-spondin1 Controls Muscle Cell Fusion through Dual Regulation of Antagonistic Wnt Signaling Pathways

Wnt-mediated signals are involved in many important steps in mammalian regeneration. In multiple cell types, the R-spondin (Rspo) family of secreted proteins potently activates the canonical Wnt/β-catenin pathway. Here, we identify Rspo1 as a mediator of skeletal muscle tissue repair. First, we show that deletion of Rspo1 results in global alteration of muscle regeneration kinetics following acute injury. We find that muscle progenitor cells lacking Rspo1 show delayed differentiation due to reduced activation of Wnt/β-catenin target genes. Furthermore, muscle cells lacking Rspo1 have a fusion phenotype leading to larger myotubes containing supernumerary nuclei both in vitro and in vivo. The increase in muscle fusion was dependent on downregulation of Wnt/β-catenin and upregulation of non-canonical Wnt7a/Fzd7/Rac1 signaling. We conclude that reciprocal control of antagonistic Wnt signaling pathways by Rspo1 in muscle stem cell progeny is a key step ensuring normal tissue architecture restoration following acute damage.

Function of the myogenic regulatory factors Myf5, MyoD, Myogenin and MRF4 in skeletal muscle, satellite cells and regenerative myogenesis

Discovery of the myogenic regulatory factor family of transcription factors MYF5, MYOD, Myogenin and MRF4 was a seminal step in understanding specification of the skeletal muscle lineage and control of myogenic differentiation during development. These factors are also involved in specification of the muscle satellite cell lineage, which becomes the resident stem cell compartment inadult skeletal muscle. While MYF5, MYOD, Myogenin and MRF4 have subtle roles in mature muscle, they again play a crucial role in directing satellite cell function to regenerate skeletal muscle: linking the genetic control of developmental and regenerative myogenesis. Here, I review the role of the myogenic regulatory factors in developing and mature skeletal muscle, satellite cell specification and muscle regeneration.

Active GSK3β and an intact β-catenin TCF complex are essential for the differentiation of human myogenic progenitor cells

Wnt-β-catenin signalling is essential for skeletal muscle myogenesis during development, but its role in adult human skeletal muscle remains unknown. Here we have used human primary CD56^Pos satellite cell-derived myogenic progenitors obtained from healthy individuals to study the role of Wnt-β-catenin signalling in myogenic differentiation. We show that dephosphorylated β-catenin (active-β-catenin), the central effector of the canonical Wnt cascade, is strongly upregulated at the onset of differentiation and undergoes nuclear translocation as differentiation progresses. To establish the role of Wnt signalling in regulating the differentiation process we manipulated key nodes of this pathway through a series of β-catenin gain-of-function (GSK3 inhibition and β-catenin overexpression) or loss-of-function experiments (dominant negative TCF4). Our data showed that manipulation of these critical pathway components led to varying degrees of disruption to the normal differentiation phenotype indicating the importance of Wnt signalling in regulating this process. We reveal an independent necessity for active-β-catenin in the fusion and differentiation of human myogenic progenitors and that dominant negative inhibition of TCF4 prevents differentiation completely. Together these data add new mechanistic insights into both Wnt signalling and adult human myogenic progenitor differentiation.

Intestinal stem cell overproliferation resulting from inactivation of the APC tumor suppressor requires the transcription cofactors Earthbound and Erect wing

Wnt/β-catenin signal transduction directs intestinal stem cell (ISC) proliferation during homeostasis. Hyperactivation of Wnt signaling initiates colorectal cancer, which most frequently results from truncation of the tumor suppressor Adenomatous polyposis coli (APC). The β-catenin-TCF transcription complex activates both the physiological expression of Wnt target genes in the normal intestinal epithelium and their aberrantly increased expression in colorectal tumors. Whether mechanistic differences in the Wnt transcription machinery drive these distinct levels of target gene activation in physiological versus pathological states remains uncertain, but is relevant for the design of new therapeutic strategies. Here, using a Drosophila model, we demonstrate that two evolutionarily conserved transcription cofactors, Earthbound (Ebd) and Erect wing (Ewg), are essential for all major consequences of Apc1 inactivation in the intestine: the hyperactivation of Wnt target gene expression, excess number of ISCs, and hyperplasia of the epithelium. In contrast, only Ebd, but not Ewg, mediates the Wnt-dependent regulation of ISC proliferation during homeostasis. Therefore, in the adult intestine, Ebd acts independently of Ewg in physiological Wnt signaling, but cooperates with Ewg to induce the hyperactivation of Wnt target gene expression following Apc1 loss. These findings have relevance for human tumorigenesis, as Jerky (JRK/JH8), the human Ebd homolog, promotes Wnt pathway hyperactivation and is overexpressed in colorectal, breast, and ovarian cancers. Together, our findings reveal distinct requirements for Ebd and Ewg in physiological Wnt pathway activation versus oncogenic Wnt pathway hyperactivation following Apc1 loss. Such differentially utilized transcription cofactors may offer new opportunities for the selective targeting of Wnt-driven cancers.

Canonical Wnt signalling regulates nuclear export of Setdb1 during skeletal muscle terminal differentiation

The histone 3 lysine 9 methyltransferase Setdb1 is essential for both stem cell pluripotency and terminal differentiation of different cell types. To shed light on the roles of Setdb1 in these mutually exclusive processes, we used mouse skeletal myoblasts as a model of terminal differentiation. Ex vivo studies on isolated single myofibres showed that Setdb1 is required for adult muscle stem cells expansion following activation. In vitro studies in skeletal myoblasts confirmed that Setdb1 suppresses terminal differentiation. Genomic binding analyses showed a release of Setdb1 from selected target genes upon myoblast terminal differentiation, concomitant to a nuclear export of Setdb1 to the cytoplasm. Both genomic release and cytoplasmic Setdb1 relocalisation during differentiation were dependent on canonical Wnt signalling. Transcriptomic assays in myoblasts unravelled a significant overlap between Setdb1 and Wnt3a regulated genetic programmes. Together, our findings revealed Wnt-dependent subcellular relocalisation of Setdb1 as a novel mechanism regulating Setdb1 functions and myogenesis.

β-Catenin Activation in Muscle Progenitor Cells Regulates Tissue Repair

Skeletal muscle regeneration relies on a pool of resident muscle stem cells called satellite cells (MuSCs). Following injury-induced destruction of the myofibers, quiescent MuSCs are activated and generate transient amplifying progenitors (myoblasts) that will fuse to form new myofibers. Here, we focus on the canonical Wnt signaling pathway and find that either conditional β-catenin disruption or activation in adult MuSCs results in perturbation of muscle regeneration. Using both in vivo and in vitro approaches, we observed that myoblasts lacking β-catenin show delayed differentiation, whereas myoblasts with constitutively active β-catenin undergo precocious growth arrest and differentiation. Transcriptome analysis further demonstrated that Wnt/β-catenin signaling interacts with multiple pathways and, more specifically, TGF-β signaling. Indeed, exogenous TGF-β2 stimulation restores the regenerative potential of muscles with targeted β-catenin disruption in MuSCs. We conclude that a precise level of β-catenin activity is essential for regulating the amplification and differentiation of MuSC descendants during adult myogenesis.

Hepatocyte Growth Factor and Satellite Cell Activation

Satellite cells are the "currency" for the muscle growth that is critical to meat production in many species, as well as to phenotypic distinctions in development at the level of species or taxa, and for human muscle growth, function and regeneration. Careful research on the activation and behaviour of satellite cells, the stem cells in skeletal muscle, including cross-species comparisons, has potential to reveal the mechanisms underlying pathological conditions in animals and humans, and to anticipate implications of development, evolution and environmental change on muscle function and animal performance.

BCL9/9L-β-catenin Signaling is Associated With Poor Outcome in Colorectal Cancer

BCL9/9L proteins enhance the transcriptional output of the β-catenin/TCF transcriptional complex and contribute critically to upholding the high WNT signaling level required for stemness maintenance in the intestinal epithelium. Here we show that a BCL9/9L-dependent gene signature derived from independent mouse colorectal cancer (CRC) models unprecedentedly separates patient subgroups with regard to progression free and overall survival. We found that this effect was by and large attributable to stemness related gene sets. Remarkably, this signature proved associated with recently described poor prognosis CRC subtypes exhibiting high stemness and/or epithelial-to-mesenchymal transition (EMT) traits. Consistent with the notion that high WNT signaling is required for stemness maintenance, ablating Bcl9/9l-β-catenin in murine oncogenic intestinal organoids provoked their differentiation and completely abrogated their tumorigenicity, while not affecting their proliferation. Therapeutic strategies aimed at targeting WNT responses may be limited by intestinal toxicity. Our findings suggest that attenuating WNT signaling to an extent that affects stemness maintenance without disturbing intestinal renewal might be well tolerated and prove sufficient to reduce CRC recurrence and dramatically improve disease outcome.

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Inhibiting BCL9/9L-β-catenin in CRC models reduces stemness and boosts differentiation traits

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CRC patients with low expression of BCL9/9L-β-catenin regulated genes have a better prognosis

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Tempering WNT signaling without affecting intestinal self renewal might be an attractive therapeutic strategy in CRC

Mutational activation of the WNT pathway is a key oncogenic event in colorectal cancer (CRC). Targeting the WNT pathway therefore appears as an attractive strategy, but the therapeutic window might be limited due to intestinal toxicity. Maximum WNT signaling strength is required for upholding stemness traits, which are linked to poor prognosis in CRC. Our data suggest that tempering WNT signaling through abrogating BCL9/9L-β-catenin signaling in CRC models is tolerable for intestinal homeostasis yet strongly diminishes stemness traits and may have a vast impact on CRC patient outcome.

Inhibition of Wnt/β-catenin pathway promotes regenerative repair of cutaneous and cartilage injury

Wound healing in mammals is a fibrotic process. The mechanisms driving fibrotic (as opposed to regenerative) repair are poorly understood. Herein we report that therapeutic Wnt inhibition with topical application of small-molecule Wnt inhibitors can reduce fibrosis and promote regenerative cutaneous wound repair. In the naturally stented model of ear punch injury, we found that Wnt/β-catenin pathway is activated most notably in the dermis of the wound bed early (d 2) after injury and subsides to baseline levels by d10. Topical application of either of 2 mechanistically distinct small-molecule Wnt pathway inhibitors (a tankyrase inhibitor, XAV-939, and the U.S. Food and Drug Administration-approved casein kinase activator, pyrvinium) in C57Bl/6J mice resulted in significantly increased rates of wound closure (72.3 ± 14.7% with XAV-939; and 52.1 ± 20.9% with pyrvinium) compared with contralateral controls (38.1 ± 23.0 and 40.4.± 16.7%, respectively). Histologically, Wnt inhibition reduced fibrosis as measured by α-smooth muscle actin positive myofibroblasts and collagen type I α1 synthesis. Wnt inhibition also restored skin architecture including adnexal structures in ear wounds and dermal-epidermal junction with rete pegs in excisional wounds. Additionally, in ear punch injury Wnt inhibitor treatment enabled regeneration of auricular cartilage. Our study shows that pharmacologic Wnt inhibition holds therapeutic utility for regenerative repair of cutaneous wounds.

Wnt/β-catenin controls follistatin signalling to regulate satellite cell myogenic potential

BACKGROUND

Adult skeletal muscle regeneration is a highly orchestrated process involving the activation and proliferation of satellite cells, an adult skeletal muscle stem cell. Activated satellite cells generate a transient amplifying progenitor pool of myoblasts that commit to differentiation and fuse into multinucleated myotubes. During regeneration, canonical Wnt signalling is activated and has been implicated in regulating myogenic lineage progression and terminal differentiation.

METHODS

Here, we have undertaken a gene expression analysis of committed satellite cell-derived myoblasts to examine their ability to respond to canonical Wnt/β-catenin signalling.

RESULTS

We found that activation of canonical Wnt signalling induces follistatin expression in myoblasts and promotes myoblast fusion in a follistatin-dependent manner. In growth conditions, canonical Wnt/β-catenin signalling prime myoblasts for myogenic differentiation by stimulating myogenin and follistatin expression. We further found that myogenin binds elements in the follistatin promoter and thus acts downstream of myogenin during differentiation. Finally, ectopic activation of canonical Wnt signalling in vivo promoted premature differentiation during muscle regeneration following acute injury.

CONCLUSIONS

Together, these data reveal a novel mechanism by which myogenin mediates the canonical Wnt/β-catenin-dependent activation of follistatin and induction of the myogenic differentiation process.

Coordinated action of Axin1 and Axin2 suppresses β-catenin to regulate muscle stem cell function

The resident stem cells of skeletal muscle are satellite cells, which are regulated by both canonical and non-canonical Wnt pathways. Canonical Wnt signalling promotes differentiation, and is controlled at many levels, including via Axin1 and Axin2-mediated β-catenin degradation. Axin1 and Axin2 are thought equivalent suppressors of canonical Wnt signalling, although Axin2 is also a Wnt target gene. We show that Axin1 expression was higher in proliferating satellite cells, while Axin2 was up-regulated during differentiation. siRNA-mediated Axin1 knockdown changed cell morphology, suppressed proliferation and promoted myogenic differentiation. Simultaneous knockdown of both Axin1 and β-catenin rescued proliferation and partially, premature differentiation. Surprisingly, retroviral-mediated overexpression of Axin2 was unable to compensate for knockdown of Axin1 in satellite cells, indicating that Axin1 and Axin2 are not fully redundant. Isolated satellite cells from Axin2-null mice also had no major phenotype. However, siRNA-mediated knockdown of Axin1 in Axin2-null cells strongly inhibited proliferation, while inducing differentiation, clear nuclear localisation of β-catenin, up-regulation of canonical Wnt target genes (Axin2, Lef1, Tcf4, Pitx2c and Lgr5) and activation of a TCF reporter construct. Again, concomitant knockdown of Axin1 and β-catenin in Axin2-null satellite cells rescued morphology and proliferation, but only partially prevented precocious differentiation. Thus, Axin1 and Axin2 do not have equivalent functions in satellite cells, but are both involved in repression of Wnt/β-catenin signalling to maintain proliferation and contribute to controlling timely myogenic differentiation.

Chromatin signaling in muscle stem cells: interpreting the regenerative microenvironment

Muscle regeneration in the adult occurs in response to damage at expenses of a population of adult stem cells, the satellite cells. Upon injury, either physical or genetic, signals released within the satellite cell niche lead to the commitment, expansion and differentiation of the pool of muscle progenitors to repair damaged muscle. To achieve this goal satellite cells undergo a dramatic transcriptional reprogramming to coordinately activate and repress specific subset of genes. Although the epigenetics of muscle regeneration has been extensively discussed, less emphasis has been put on how extra-cellular cues are translated into the specific chromatin reorganization necessary for progression through the myogenic program. In this review we will focus on how satellite cells sense the regenerative microenvironment in physiological and pathological circumstances, paying particular attention to the mechanism through which the external stimuli are transduced to the nucleus to modulate chromatin structure and gene expression. We will discuss the pathways involved and how alterations in this chromatin signaling may contribute to satellite cells dysfunction during aging and disease.

Brain and muscle Arnt-like 1 promotes skeletal muscle regeneration through satellite cell expansion

Circadian clock is an evolutionarily conserved timing mechanism governing diverse biological processes and the skeletal muscle possesses intrinsic functional clocks. Interestingly, although the essential clock transcription activator, Brain and muscle Arnt-like 1 (Bmal1), participates in maintenance of muscle mass, little is known regarding its role in muscle growth and repair. In this report, we investigate the in vivo function of Bmal1 in skeletal muscle regeneration using two muscle injury models. Bmal1 is highly up-regulated by cardiotoxin injury, and its genetic ablation significantly impairs regeneration with markedly suppressed new myofiber formation and attenuated myogenic induction. A similarly defective regenerative response is observed in Bmal1-null mice as compared to wild-type controls upon freeze injury. Lack of satellite cell expansion accounts for the regeneration defect, as Bmal1(-/-) mice display significantly lower satellite cell number with nearly abolished induction of the satellite cell marker, Pax7. Furthermore, satellite cell-derived primary myoblasts devoid of Bmal1 display reduced growth and proliferation ex vivo. Collectively, our results demonstrate, for the first time, that Bmal1 is an integral component of the pro-myogenic response that is required for muscle repair. This mechanism may underlie its role in preserving adult muscle mass and could be targeted therapeutically to prevent muscle-wasting diseases.

Maternal nutrition induces gene expression changes in fetal muscle and adipose tissues in sheep

Background

Maternal nutrition during different stages of pregnancy can induce significant changes in the structure, physiology, and metabolism of the offspring. These changes could have important implications on food animal production especially if these perturbations impact muscle and adipose tissue development. Here, we evaluated the impact of different maternal isoenergetic diets, alfalfa haylage (HY; fiber), corn (CN; starch), and dried corn distillers grains (DG; fiber plus protein plus fat), on the transcriptome of fetal muscle and adipose tissues in sheep.

Results

Prepartum diets were associated with notable gene expression changes in fetal tissues. In longissimus dorsi muscle, a total of 224 and 823 genes showed differential expression (FDR ≤0.05) in fetuses derived from DG vs. CN and HY vs. CN maternal diets, respectively. Several of these significant genes affected myogenesis and muscle differentiation. In subcutaneous and perirenal adipose tissues, 745 and 208 genes were differentially expressed (FDR ≤0.05), respectively, between CN and DG diets. Many of these genes are involved in adipogenesis, lipogenesis, and adipose tissue development. Pathway analysis revealed that several GO terms and KEGG pathways were enriched (FDR ≤0.05) with differentially expressed genes associated with tissue and organ development, chromatin biology, and different metabolic processes.

Conclusions

These findings provide evidence that maternal nutrition during pregnancy can alter the programming of fetal muscle and fat tissues in sheep. The ramifications of the observed gene expression changes, in terms of postnatal growth, body composition, and meat quality of the offspring, warrant future investigation.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-1034) contains supplementary material, which is available to authorized users.

Pax6-dependent, but β-catenin-independent, function of Bcl9 proteins in mouse lens development

Bcl9 and Bcl9l (Bcl9/9l) encode Wnt signaling components that mediate the interaction between β-catenin and Pygo. Cantù et al. find that Bcl9/9l contribute in a Pygo-dependent, but β-catenin-independent, fashion to eye lens formation. Pax6, the master regulator of eye differentiation, directly activates Bcl9 and Bcl9l transcription.

Bcl9 and Bcl9l (Bcl9/9l) encode Wnt signaling components that mediate the interaction between β-catenin and Pygopus (Pygo) via two evolutionarily conserved domains, HD1 and HD2, respectively. We generated mouse strains lacking these domains to probe the β-catenin-dependent and β-catenin-independent roles of Bcl9/9l and Pygo during mouse development. While lens development is critically dependent on the presence of the HD1 domain, it is not affected by the lack of the HD2 domain, indicating that Bcl9/9l act in this context in a β-catenin-independent manner. Furthermore, we uncover a new regulatory circuit in which Pax6, the master regulator of eye development, directly activates Bcl9/9l transcription.

Crosstalk between microRNA30a/b/c/d/e-5p and the canonical Wnt pathway: implications for multiple myeloma therapy

Dysregulation of transcription via the Wnt/β-catenin signaling pathway underlies the pathogenesis of a wide variety of frequent human cancers. These include epithelial carcinomas such as colorectal cancer and hematologic malignancies such as multiple myeloma. Thus, the Wnt/β-catenin in pathway potentially offers an attractive target for cancer therapy. This approach, however, has thus far proved challenging because the pathway plays a number of critical roles in physiologic homeostasis, [corrected] and because drugs that broadly target the pathway have unacceptable side effects. miRNAs function as regulators of gene expression and have also been implicated in the pathogenesis of multiple myeloma and other human cancers, offering the promise of novel therapeutic approaches if they can be applied effectively in vivo. Because BCL9 is a critical transcriptional coactivator of β-catenin that is aberrantly expressed in many human cancers but is of low abundance in normal tissues, [corrected] the Wnt/β-catenin/BCL9 complex has emerged as a promising and most likely relatively safe therapeutic target in cancers with dysregulated Wnt/β-catenin activity. This review discusses recent advances in the biology of Wnt inhibitors and the appealing possibility of a functional link between BCL9 and miRNA30a/b/c/d/e-5p that could be exploited for multiple myeloma therapy.

Transiently active Wnt/β-catenin signaling is not required but must be silenced for stem cell function during muscle regeneration

Adult muscle’s exceptional capacity for regeneration is mediated by muscle stem cells, termed satellite cells. As with many stem cells, Wnt/β-catenin signaling has been proposed to be critical in satellite cells during regeneration. Using new genetic reagents, we explicitly test in vivo whether Wnt/β-catenin signaling is necessary and sufficient within satellite cells and their derivatives for regeneration. We find that signaling is transiently active in transit-amplifying myoblasts, but is not required for regeneration or satellite cell self-renewal. Instead, downregulation of transiently activated β-catenin is important to limit the regenerative response, as continuous regeneration is deleterious. Wnt/β-catenin activation in adult satellite cells may simply be a vestige of their developmental lineage, in which β-catenin signaling is critical for fetal myogenesis. In the adult, surprisingly, we show that it is not activation but rather silencing of Wnt/β-catenin signaling that is important for muscle regeneration.

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Wnt/β-catenin signaling is transiently active in myoblasts during muscle regeneration

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β-catenin is not required in myogenic cells for muscle regeneration

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β-catenin signaling in myoblasts must be silenced to limit the regenerative response

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β-catenin requirement and sensitivity differs in fetal and adult muscle stem cells

Making skeletal muscle from progenitor and stem cells: development versus regeneration

For locomotion, vertebrate animals use the force generated by contractile skeletal muscles. These muscles form an actin/myosin-based biomachinery that is attached to skeletal elements to affect body movement and maintain posture. The mechanics, physiology, and homeostasis of skeletal muscles in normal and disease states are of significant clinical interest. How muscles originate from progenitors during embryogenesis has attracted considerable attention from developmental biologists. How skeletal muscles regenerate and repair themselves after injury by the use of stem cells is an important process to maintain muscle homeostasis throughout lifetime. In recent years, much progress has been made toward uncovering the origins of myogenic progenitors and stem cells as well as the regulation of these cells during development and regeneration.

From SNP co-association to RNA co-expression: novel insights into gene networks for intramuscular fatty acid composition in porcine

Background

Fatty acids (FA) play a critical role in energy homeostasis and metabolic diseases; in the context of livestock species, their profile also impacts on meat quality for healthy human consumption. Molecular pathways controlling lipid metabolism are highly interconnected and are not fully understood. Elucidating these molecular processes will aid technological development towards improvement of pork meat quality and increased knowledge of FA metabolism, underpinning metabolic diseases in humans.

Results

The results from genome-wide association studies (GWAS) across 15 phenotypes were subjected to an Association Weight Matrix (AWM) approach to predict a network of 1,096 genes related to intramuscular FA composition in pigs. To identify the key regulators of FA metabolism, we focused on the minimal set of transcription factors (TF) that the explored the majority of the network topology. Pathway and network analyses pointed towards a trio of TF as key regulators of FA metabolism: NCOA2, FHL2 and EP300. Promoter sequence analyses confirmed that these TF have binding sites for some well-know regulators of lipid and carbohydrate metabolism. For the first time in a non-model species, some of the co-associations observed at the genetic level were validated through co-expression at the transcriptomic level based on real-time PCR of 40 genes in adipose tissue, and a further 55 genes in liver. In particular, liver expression of NCOA2 and EP300 differed between pig breeds (Iberian and Landrace) extreme in terms of fat deposition. Highly clustered co-expression networks in both liver and adipose tissues were observed. EP300 and NCOA2 showed centrality parameters above average in the both networks. Over all genes, co-expression analyses confirmed 28.9% of the AWM predicted gene-gene interactions in liver and 33.0% in adipose tissue. The magnitude of this validation varied across genes, with up to 60.8% of the connections of NCOA2 in adipose tissue being validated via co-expression.

Conclusions

Our results recapitulate the known transcriptional regulation of FA metabolism, predict gene interactions that can be experimentally validated, and suggest that genetic variants mapped to EP300, FHL2, and NCOA2 modulate lipid metabolism and control energy homeostasis in pigs.

GSK3β inhibition and LEF1 upregulation in skeletal muscle following a bout of downhill running

Canonical Wnt signaling is important in skeletal muscle repair but has not been well characterized in response to physiological stimuli. The objective of this study was to assess the effect of downhill running (DHR) on components of Wnt signaling. Young, male C57BL/J6 mice were exposed to DHR. Muscle injury and repair (MCadherin) were measured in soleus. Gene and protein expression of Wnt3a, active β-catenin, GSK3β, and LEF1 were measured in gastrocnemius. Muscle injury increased 6 days post-DHR and MCadherin protein increased 5 days post-DHR. Total and active GSK3β protein decreased 3 days (9-fold and 3.6-fold, respectively) post-DHR. LEF1 protein increased 6 days (5-fold) post-DHR. DHR decreased GSK3β and increased LEF1 protein expression, but did not affect other components of Wnt signaling. Due to their applicability, using models of physiological stimuli such as DHR will provide significant insight into cellular mechanisms within muscle.

Wnt-related genes and large-joint osteoarthritis: association study and replication

Osteoarthritis (OA) has a strong genetic component, and experimental evidence suggests the involvement of the Wnt pathway in its pathogenesis. Hence, we explored the association of common single nucleotide polymorphisms (SNPs) related to the Wnt pathway with hip and knee OA. Seventy-eight SNPs were analyzed in 606 patients undergoing joint replacement and in 680 control subjects. SNPs were located in WNT1, WNT10A, WNT16, DVL2, FZD5, BCL9, SFRP1, TCF7L1 and SFRP4 genes. SNPs significantly associated with OA were genotyped in an independent group of 369 patients and 407 controls. One SNP in WNT10A, rs3806557, was associated with hip OA in men (OR 0.65, 95% CI 0.46-0.93; p = 0.017), but the association was not confirmed in the replication phase. The TCF7L1 polymorphism rs11547160 was also associated with hip OA in the discovery set, but not in the replication set. Similarly, the SFRP4 SNP rs1052981 was associated with knee OA in women with OR of 2.73 (95% CI 1.29-5.8; p = 0.006), but the association was not replicated. The BCL9 polymorphism rs2353525 was associated with knee OA in women, both in the unadjusted and in the age- and BMI-adjusted analysis (OR 2.01; 95% CI 1.34-2.98; p = 0.0006). A similar, but not statistically significant, trend was observed in the replication phase. In the combined analysis, OR was 3.13 (1.34-7.28; p = 0.009). These data suggest that some SNPs of genes related to the Wnt pathway and, specifically BCL9, influence the genetic predisposition to osteoarthritis of the large joints in a sex- and joint-specific way.

An emerging role for Wnt and GSK3 signaling pathways in schizophrenia

Schizophrenia is a disabling illness with limited treatment options. The underlying pathophysiology remains unknown, partially due to its heterogeneous nature, and a lack of understanding of the biological functions of genetic risk factors. Several signaling pathways have been implicated, however, with the varying degrees of support. In this article, I will focus on the converging evidence supporting a prominent role for Wnt and glycogen synthase kinase 3 (GSK3) signaling in the biological bases of schizophrenia. This includes current pharmacological therapies that target GSK3, animal model and cell-based studies, and recent human genetic findings that implicate Wnt and GSK3 signaling.

Satellite cells are essential for skeletal muscle regeneration: the cell on the edge returns centre stage

Following their discovery in 1961, it was speculated that satellite cells were dormant myoblasts, held in reserve until required for skeletal muscle repair. Evidence for this accumulated over the years, until the link between satellite cells and the myoblasts that appear during muscle regeneration was finally established. Subsequently, it was demonstrated that, when grafted, satellite cells could also self-renew, conferring on them the coveted status of 'stem cell'. The emergence of other cell types with myogenic potential, however, questioned the precise role of satellite cells. Here, we review recent recombination-based studies that have furthered our understanding of satellite cell biology. The clear consensus is that skeletal muscle does not regenerate without satellite cells, confirming their pivotal and non-redundant role.

Wnt signaling in myogenesis

The formation of skeletal muscle is a tightly regulated process that is critically modulated by Wnt signaling. Myogenesis is dependent on the precise and dynamic integration of multiple Wnt signals allowing self-renewal and progression of muscle precursors in the myogenic lineage. Dysregulation of Wnt signaling can lead to severe developmental defects and perturbation of muscle homeostasis. Recent work has revealed novel roles for the non-canonical planar cell polarity (PCP) and AKT/mTOR pathways in mediating the effects of Wnt on skeletal muscle. In this review, we discuss the role of Wnt signaling in myogenesis and in regulating the homeostasis of adult muscle.