BACKGROUND: The regeneration of muscle cells from stem cells is an intricate process, and various genes are included in the process such as myoD, mf5, mf6, etc. The key genes and pathways in the differentiating stages are various. Therefore, the differential expression of key genes after 4 weeks of differentiation were investigated in our study.
METHODS: Three published gene expression profiles, GSE131125, GSE148994, and GSE149055, about the comparisons of pluripotent stem cells to differentiated cells after 4 weeks were obtained from the Gene Expression Omnibus (GEO) database. Common differentially expressed genes (DEGs) were obtained for further analysis such as protein-protein interaction (PPI) network, Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), and GSEA analysis. After hub genes and key pathways were obtained, we manipulated in vitro cell research for substantiation such as immunohistochemical staining and semi-quantitative analysis and quantitative real-time PCR.
RESULTS: A total of 824 DEGs including 350 upregulated genes and 474 downregulated genes were identified in the three GSEs. Nineteen hub genes were identified from the PPI network. The GO and KEGG pathway analyses confirmed that myogenic differentiation at 4 weeks was strongly associated with pathway in cancer, PI3K pathway, actin cytoskeleton regulation and metabolic pathway, biosynthesis of antibodies, and cell cycle. GSEA analysis indicated the differentiated cells were enriched in muscle cell development and myogenesis. Meanwhile, the core genes in each pathway were identified from the GSEA analysis. The in vitro cell research revealed that actin cytoskeleton and myoD were upregulated after 4-week differentiation.
CONCLUSIONS: The research revealed the potential hub genes and key pathways after 4-week differentiation of stem cells which contribute to further study about the molecular mechanism of myogenesis regeneration, paving a way for more accurate treatment for muscle dysfunction.

BACKGROUND: Spindle cell/sclerosing rhabdomyosarcoma is a genomically heterogeneous, uncommon subtype of rhabdomyosarcoma, particularly rare in adults. Its MYOD1-mutant variant is aggressive irrespective of age. Cytogenetic data on spindle cell/sclerosing rhabdomyosarcoma are sparse and disparate.
METHODS: Cytogenetic and molecular analyses were performed on an adult sclerosing rhabdomyosarcoma.
RESULTS: The karyotype of the sclerosing rhabdomyosarcoma displayed clonal evolution corresponding to two hyperdiploid clones: 48,XY,+i(19)(p10),+22/48,idem,der(9)t(2;9)(q21~22;p21). The changes were gain of chromosome 19 with the overrepresentation of 19p arm, gain of chromosome 22, gain of the 2q arm, and loss of 9p21. Mutation analysis revealed a homozygous c.T365G (p.L122R) mutation of the MYOD1 gene, but none of PIK3CA.
CONCLUSIONS: To our knowledge, this is the first adult MYOD1-mutant sclerosing rhabdomyosarcoma studied cytogenetically. The only other reported sclerosing rhabdomyosarcoma with MYOD1 mutation and abnormal karyotype was pediatric. Since these tumors are highly aggressive, further studies unravelling their cytogenetic and molecular characteristics are warranted.

Objective: To study the clinicopathological features and immunophenotype of spindle cell/sclerosing rhabdomyosarcoma (SRMS) in adults and children, as well as its correlation with the expression and gene-mutations of MYOD1. Methods: Twenty cases of SRMS were collected at Xijing Hospital, Fourth Military Medical University from 2009 to 2019. These cases were evaluated for clinical, pathological, and immunohistochemical features. MYOD1 gene sequencing was performed on 12 cases with available tissue and sufficient DNA quantity using Sanger sequencing. Results: The 20 patients included 12 children and 8 adults, 11 males and 9 females, with an age range of 8 months to 85 years (mean 22 years). Most of them presented with a painless, progressively enlarged solid mass. The tumors occurred in head and neck (7 cases), abdominal and pelvic cavity (7 cases, including 4 in abdominal cavity, 2 in pelvic cavity, 1 in abdominal and left thoracic cavity), upper limb (5 cases, including 2 in left shoulder, 1 in right armpit, 1 in right humerus, and 1 in left forearm), and the back (1 case). The diameter of these tumors ranged from 2.5 to 20 cm, with a mean of 6.2 cm. Histologically, all of the tumors were mainly composed of spindle cells arranged in fascicles, and in 7 cases, at least in part, arranged in herringbone pattern, resembling adult fibrosarcoma. Foci reminiscent of interstitial sclerosing were presented in 4 cases, pseudovascular structures in 2 cases, loosely myxoid stroma in 4 cases, and varying degree of necrosis in 9 cases. A various number of spindled or polygonal rhabdomyoblasts were observed between spindle cells in 3 cases.Among them,16 cases showed spindle cell morphology, 2 cases showed scleroisng morphology, and 2 cases showed a hybrid phenotype of spindle, sclerosing and primitive undifferentiated areas. Immunohistochemically, the tumor cells were positive for desmin, Myogenin and/or MyoD1, but negative for CKpan, ALK1, CD34, EMA, HMB45, SMA, H-cald and S-100. Four cases (4/12) harbored a homozygous or heterozygous MYOD1 (p.L122R) mutation. MYOD1-mutant SRMS usually had diffuse and strong nuclear MyoD1 positivity. Follow-up was available in 12 cases, ranged from 1 to 51 months. At the end of follow-up period, 3 patients died of the disease, 3 patients developed local recurrences, 2 patients survived with disease. Conclusions: SRMS is a rare type of rhabdomyosarcoma, and more commonly occurs in the head and neck of children than adults. MYOD1-mutant SRMS usually had diffuse and strong nuclear MyoD1 positivity, frequently associated with a more aggressive behavior.
目的： 探讨梭形细胞/硬化性横纹肌肉瘤（spindle cell/sclerosing rhabdomyosarcoma, SRMS）的临床病理学特征、免疫表型，及MyoD1表达与基因突变的关系。 方法： 收集2009至2019年20例空军军医大学（第四军医大学）西京医院SRMS病例资料和切片。对肿瘤切除标本进行组织学形态和免疫组织化学EnVision染色，对12例进行MYOD1基因Sanger法测序分析。 结果： 20例包括儿童12例和成人8例，其中男性11例，女性9例，年龄8个月至85岁，平均22岁。患者临床主要表现为逐渐增大的无痛性肿块。发生于头颈部7例，腹盆腔7例（腹腔4例、盆腔2例、左侧胸腹腔1例），上肢5例（左肩部2例、右腋下1例、右肱骨1例、左前臂1例），背部1例。肿瘤直径2.5~20.0 cm，平均6.2 cm。病理组织学观察，肿瘤主要由梭形细胞组成，呈束状排列，其中7例至少部分区域呈鱼骨样或人字形的束状排列，似成人型纤维肉瘤；4例可见不同程度明显的间质硬化，2例局部可见血管外皮细胞瘤样结构，4例出现疏松黏液样区域，9例可见不同程度的坏死灶。有3例在梭形细胞之间有少量的梭形或多角形的横纹肌母细胞。在该组病例中，16例为纯梭形细胞，2例为纯硬化性，2例为梭形细胞/硬化性混合性横纹肌肉瘤。免疫组织化学显示，梭形细胞均为结蛋白阳性，以及Myogenin和/或MyoD1不同程度阳性；而其他标志物，如广谱细胞角蛋白、间变性淋巴瘤激酶1、CD34、上皮细胞膜抗原、HMB45、H-cald、平滑肌肌动蛋白和S-100蛋白均阴性。12例测序病例中，有4例（4/12）检测到MYOD1基因p.L122R位点突变。有效随访12例，时间1~51个月，3例因多发转移死亡，3例复发，2例带瘤生存。 结论： SRMS是少见类型的横纹肌肉瘤，好发于头颈部，多见于儿童，成人较少见。有MYOD1基因突变的SRMS通常有弥漫的MyoD1核阳性，与更具有侵袭性的生物学行为有关。.

Rhabdomyosarcoma is the most common sarcoma diagnosed in childhood and adolescence, arising from the bladder/prostate in only 5%-10% of cases. Treatment-induced cytodifferention of tumor cells into mature rhabdomyoblasts has been reported following chemoradiation and is thought to suggest a more favorable outcome. We report a case of embryonal rhabdomyosarcoma of the bladder/prostate that exhibited extensive cytodifferentiation with downregulation of myogenin and MyoD1 gene expression in rhabdomyoblasts following treatment with chemoradiation therapy. The downregulation of myogenin and MyoD1 expression in rhabdomyoblasts following chemoradiation treatment has not previously been described in the literature and its significant remains uncertain.

Dedifferentiation is a loss of phenotypic specialization that converts differentiated cells into adult stem cells in order to proliferate and differentiate into replacement tissue. This occurs in several tissues from various organs, such as smooth muscle cells (SMCs) of the mammalian gastrointestinal tract. The aim of this study was to describe ultrastructural and immunohistochemical changes in SMCs which could be compatible with a dedifferentiation process in human and rabbit intestinal muscles. Ultrastructural study and immunohistochemical staining (SMemb and MyoD) on human and rabbit duodenum tissue sections were performed. In both species, this dedifferentiation process is characterized by a loss of intercellular junctions, increased intercellular spaces, cytoskeletal disorganization, perinuclear accumulation of large vacuoles that tend to fuse, rupture of the vacuole membrane and release of cytoplasmic fragments. Dedifferentiated cells show the characteristic phenotype of a mesenchymal cell with scarce perinuclear cytoplasm, long cytoplasmic prolongations and finely distributed granular chromatin in the nucleus. These morphological changes are accompanied by a modulation to a less mature phenotype showing immunoreactivity for the embryonic form of the myosin heavy chain and for the myogenic regulatory factor MyoD. We suggest that SMC dedifferentiation includes the elimination of the contractile apparatus, the activation of the nucleus and the re-expression of embryonic markers. We described an ultrastructural dedifferentiation process possible in intestinal SMCs. This dedifferentiation process seems to play a key role in the homeostasis of the intestinal muscle.

To study the cellular and molecular function of peroxisome proliferator-activated receptor γ (PPARγ) in skeletal muscle differentiation, we have generated inducible gain-of-function to overexpress PPARγ in C2C12 myoblasts. In order to identify PPARγ targets, RNA sequencing (RNA-seq) was used to evaluate and quantify the transcriptomes and expression patterns during myogenic differentiation under the overexpression of PPARγ. The formation of myotubes and the expression of muscle-specific myogenic genes such as MyoD and MyoG may be inhibited by PPARγ overexpression. Multiple genes and pathways were significantly involved in this process, including 11 genes such as Fndc9 and Slc14a1 with fundamental change of regulation modes, 9 genes of which were validated by the data of qRT-PCR. Our studies demonstrate that PPARγ would play critical roles on myoblasts differentiation, mediating crosstalk among several pathways and transcription factors. Our data is available in the Gene Expression Omnibus (GEO) database with the accession number as GSE99399.

Amyotrophic Lateral Sclerosis (ALS) is a severe and fatal neurodegenerative disease characterized by progressive loss of motoneurons, muscle atrophy and paralysis. Recent evidence suggests that ALS should be considered as a multi-systemic disease, in which several cell types contribute to motoneuron degeneration. In this view, mutations in ALS linked genes in other neural and non-neural cell types may exert non-cell autonomous effects on motoneuron survival and function. Induced Pluripotent Stem Cells (iPSCs) have been recently derived from several patients with ALS mutations and it has been shown that they can generate motoneurons in vitro, providing a valuable tool to study ALS. However, the potential of iPSCs could be further valorized by generating other cell types that may be relevant to the pathology. In this paper, by taking advantage of a novel inducible system for MyoD expression, we show that both control iPSCs and iPSCs carrying mutations in ALS genes can generate skeletal muscle cells. We provide evidence that both control and mutant iPSC-derived myotubes are functionally active. This in vitro system will be instrumental to dissect the molecular and cellular pathways impairing the complex motoneuron microenvironment in ALS.

OBJECTIVE: To establish the isolation, culture and identification methods of primary rat skeletal muscle satellite cells (SMSC) and observe its characterization of differentiation in vitro.
METHODS: Skeletal muscle satellite cells were obtained by tissue block culture method in combination with pre-plating techniques, and the purity of these cells was detected by both immunocytochemistry and fluorescence activated cell sorter (FACS) with Pax7 as marker of SMSC. Myogenesis of these cells was induced in differentiation medium and the mRNA expressions of myogenic differentiation gene (MyoD) and Myogenin were determined by Real-time polymerase chain reaction (PCR).
RESULTS: Cells crawled out from the edge of tissue blocks after 1 week of culture. After purification by pre-plating techniques, more than 97.6% of the cells expressed Pax7, a unique marker of satellite cells. The mRNA of MyoD and Myogenin showed time-specific expression in the myogenesis induction process in vitro.
CONCLUSIONS: Skeletal muscle satellite cells with high purity and strong differentiation ability can be obtained by means of tissue block culture method.

Sclerosing rhabdomyosarcoma (ScRMS) and spindle cell rhabdomyosarcoma (SRMS) have been recently reclassified as a stand-alone pathologic entity, separate from embryonal RMS. Genetically, a subset of the congenital cases display NCOA2 gene rearrangements, whereas tumors occurring in older children or adults harbor MYOD1 gene mutations with or without coexisting PIK3CA mutations. Despite these recent advances, a significant number of tumors lack known genetic alterations. In this study we sought to investigate a large group of pediatric SRMS/ScRMS, spanning a diverse clinical and pathologic spectrum, by using a combined fluorescence in situ hybridization, targeted DNA, and whole-transcriptome sequencing methodology for a more definitive molecular classification. A total of 26 SRMS and ScRMS cases were selected from the 2 participating institutions for the molecular analysis. Ten of the 11 congenital/infantile SRMS showed recurrent fusion genes: with novel VGLL2 rearrangements seen in 7 (63%), including VGLL2-CITED2 fusion in 4 and VGLL2-NCOA2 in 2 cases. Three (27%) cases harbored the previously described NCOA2 gene fusions, including TEAD1-NCOA2 in 2 and SRF-NCOA2 in 1. All fusion-positive congenital/infantile SRMS patients with available long-term follow-up were alive and well, none developing distant metastases. Among the remaining 15 SRMS patients older than 1 year, 10 (67%) showed MYOD1 L122R mutations, most of them following a fatal outcome despite an aggressive multimodality treatment. All 4 cases harboring coexisting MYOD1/PIK3CA mutations shared sclerosing morphology. All 5 fusion/mutation-negative SRMS cases presented as intra-abdominal or paratesticular lesions.

BACKGROUND: Burn injury (BI) greater than 40% has been associated with protein catabolism and it is characterized by a hypermetabolic response followed for muscle loss.
OBJECTIVE: The purpose of this study was to investigate the temporal effects of extensive experimental BI in the skeletal muscle distant from lesion, through morphological analysis, expression of genes related to muscle atrophy, inflammation and the myogenic regulatory factors.
METHODS: A total of 60 young male wistar rats were distributed into two groups, control (C) and subjected to scald burn injury (SBI). The animals were euthanized 1, 4 and 14 days post-sham or 45% of the total body surface BI. The medial head of gastrocnemii muscles were submitted to histopathological, morphometric (muscle fibers area and density), MyoD and myogenin immunoexpression, and gene expression for TNF-α, iNOS and E3 ubiquitin ligases (MuRF1 and MAFbx).
RESULTS: Histopathological findings were consistent with increased amount of connective tissue and inflammatory process. Muscle fiber area of SBI groups was smaller than C and no differences were found in fiber muscle density. TNF-α was higher in SBI groups, one and 14 days post-injury; iNOS expression was higher on the first and fourth day post-injury. MuRF-1 was higher on the day four and MAFbx on the day 14.
CONCLUSIONS: In conclusion, BI causes inflammation, atrophy and myogenesis stimulation in muscle as a result of systemic host response.