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Adult Stem Cell Plasticity
Published in Richard K. Burt, Alberto M. Marmont, Stem Cell Therapy for Autoimmune Disease, 2019
Skeletal muscle derives embryologically from somites.74 Signals from adjacent embryonic structures induce myogenesis in dorsal regions of the somites, giving rise to the dermomyotome, which in turn is the major source of muscle precursor cells, termed satellite cells.75,76 Satellite cells continue to be the major source of muscle cells in the adult, despite a significant drop in their numbers during postnatal development. In aged mice, satellite cells are reduced even farther.78 These precursor cells have unique morphology and express a unique set of proteins including M-cadherin, Myf-5, CD34, and Pax-7.79,80 Satellite cells are normally quiescent, but can be activated to both self-renew and produce more committed myocyte precursors upon muscle injury or weight bearing exercise.81,82 After activation, myocyte precursors undergo multiple cycles of cell division before fusing with existing myofibers or with each other to make new myofibers.77,81,83
The skeleton and muscles
Published in Frank J. Dye, Human Life Before Birth, 2019
The myotomes of the somites (each somite is organized into two regions, sclerotome and dermomyotome) play a significant role in development, aiding the formation of muscle in the throat, neck, trunk, and limbs of the embryo.
Muscles, Soft Tissues, and Craniofacial Growth
Published in D. Dixon Andrew, A.N. Hoyte David, Ronning Olli, Fundamentals of Craniofacial Growth, 2017
The impending association between presumptive craniocervical muscles and membrane bones of the facial skeleton is established early in ontogeny, when the most rostral paraxial mesoderm condenses in the form of segmented occipital somites (see Chapter 4). The paraxial mesoderm extends even more cranially on each side of the midline, as seven incompletely segmented somitomeres that resemble immature somites (Anderson and Meier, 1981; Noden, 1982, 1983; Sperber, 1989). It has been known for many years from classical embryological studies that condensations of this most cephalic region of paraxial mesoderm contribute to cranial skeletal and muscle components, such as the sphenoid bone and the extrinsic ocular muscles (Noden, 1982). The inner aspect of the dermomyotome segment of each somite contributes to primitive muscle cells or myoblasts that become myocytes when they cease to divide.
Unique histopathologic features of the eyelid dermatofibroma
Published in Orbit, 2019
Aliaa H. Abdelhakim, Kristen E. Dunbar, Kyle J. Godfrey, Cristina Abascal Ananza, David N. Silvers, Michael Kazim
A theoretical explanation for the rarity of eyelid dermatofibroma, as well as its unique histologic features, is the embryologic origins of eyelid and noneyelid fibroblasts. Facial fibroblasts are derived from the neural crest, whereas those within the rest of the body are derived from the lateral plate mesoderm ventrally and the dermomyotome dorsally; these differences may play a role in the final behavior of the differentiated fibroblasts.14 An alternative explanation lies in the unique composition of eyelid skin. The dermis of the eyelid skin, unlike skin of the limbs or back, is predominantly composed of papillary dermis, with very little underlying reticular dermis; in contrast, reticular dermis is dominant in skin where dermatofibromas typically tend to develop.2 We believe this structural difference in the eyelid skin likely explains the eyelid-specific tumor frequency and histology discussed here.
Positive expression of PAX7 indicates poor prognosis of pediatric and adolescent AML patients
Published in Expert Review of Hematology, 2020
Tianyou Yan, Duolan Naren, Yuping Gong
PAX7 is a member of the paired box (PAX) family of transcription factors. Members of this gene family typically contain a paired box domain, an octapeptide, and a paired-type homeodomain. These genes play critical roles during fetal development and cancer growth. Furthermore, PAX7 was well studied in postnatal skeletal muscle development. In mouse skeletal muscles, PAX7 was expressed in proliferating myoblasts and was downregulated after myogenic differentiation [10]. Consistently, during differentiation of goat skeletal muscles, PAX7 expression in satellite cells was significantly downregulated [11]. PAX3 and PAX7 are co-expressed in the dermomyotome during mouse embryonic development [12]. Their expression gives rise to myogenic progenitor cells, which are necessary for myogenic development. Unlike its partner, PAX7 is predominantly required for adult myogenesis and specifies the adult stem cell population in muscles [10,13,14]. Moreover, the expression of PAX genes is also essential for growth and survival of certain cancers [15–17]. Studies showed that PAX5 expression occurs in various types of malignant tumors, including hematological malignancies, B-cell non-Hodgkin lymphoma, and Hodgkin lymphoma [17]. However, PAX7 expression is a unique feature of rhabdomyosarcoma and Ewing sarcoma [18]. In fact, PAX7 expression was present in 86% of rhabdomyosarcoma cases, and its expression was significantly increased in Ewing sarcoma compared to other soft tissue tumors, demonstrating the utility of immunohistochemical analysis of PAX7 expression as a diagnostic marker of Ewing sarcoma and rhabdomyosarcoma [18,19].