mortality/aging
muscle
• at E18.5, the genioglossus is markedly reduced
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• homozygotes display impaired primary myogenesis of most body muscles
• at E13.5, all body muscles are either absent or severely disorganized, except some deep back and head muscles
• at E13.5, at the trunk level, the external myogenic layer (cutaneus maximus) is absent while the internal myogenic layer is reduced and disorganized
• most muscles at the shoulder level are absent, the latissimus dorsi is disorganized, and the abdominal and thoracic muscles are severly reduced
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• at E13.5, homozygotes display a severe reduction and disorganisation of primary myofibers in most body muscles
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• although hypaxial progenitors are correctly specified in somites, migrate normally into the limb buds and do not undergo apoptosis, they fail to activate MyoD and myogenin at E11.5
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• at E18.5, the diaphragm is devoid of skeletal muscle fibers and appears as a thin layer of connective tissue
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• at E18.5, back intercostal muscles are present but slightly reduced
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• at E18.5, homozygotes display reduced muscle mass, especially in distal territories
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• at E18.5, homozygotes show extensive muscle hypoplasia affecting most of epaxial and hypaxial body muscles, esp. in certain hypaxial muscle groups
• at the distal forelimb level, dorsal muscles are absent and ventral muscles are strongly reduced
• at the distal hindlimb level, most ventral and intermediate muscles are absent, whereas dorsal muscles are only slightly reduced
• some superficial back muscles e.g. the trapezius, the latissimus dorsi and the serratus dorsalis are severely reduced or even absent
• at the head level, only the tongue and related muscles e.g. the genioglossus are markedly reduced
• back intercostal muscles are only slightly reduced
• reduced muscle size is due to a reduced number of myofibers; however, the decrease in the number of myofibers is quite variable in different muscles, ranging from a ~10% reduction in dorsal intercostal muscles to 50% in ventral intercostal muscles, 33% in tibialis anterior and 100% in soleus, plantaris and medial gastrocnemius
• notably, remaining myofibers are properly differentiated into fast and slow types
• in contrast to muscles, the tendons and connective tissue appear to be properly developed
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skeleton
• at E18.5, homozygotes display truncated distal ribs not attached to the sternum
• only 2 of 5 homozygotes show one or two ribs left attached to the sternum
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• at E18.5, all homozygotes display variable and asymmetric rib defects, with the right side more strongly affected
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• at E18.5, homozygotes display rib bifurcations
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rib fusion
(
J:82459
)
• at E18.5, homozygotes display fusion of cartilage segments from adjacent ribs
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• at E18.5, homozygotes show disorganized sternum ossification
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craniofacial
• at E18.5, the genioglossus is markedly reduced
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• at E18.5, the tongue and related muscles such as the genioglossus are markedly reduced
• other head muscles e.g the masseter appear correctly developed
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digestive/alimentary system
• at E18.5, the genioglossus is markedly reduced
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• at E18.5, the tongue and related muscles such as the genioglossus are markedly reduced
• other head muscles e.g the masseter appear correctly developed
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growth/size/body
• at E18.5, the genioglossus is markedly reduced
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• at E18.5, the tongue and related muscles such as the genioglossus are markedly reduced
• other head muscles e.g the masseter appear correctly developed
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