Phenotypes Associated with This Genotype

Genotype
MGI:6404227

• Allelic Composition: Neb^m1Anu/Neb^m2Anu
• Genetic Background: C57BL/6J-Neb^m1Anu Neb^m2Anu

• ♀: phenotype observed in females
• ♂: phenotype observed in males
• N: normal phenotype

muscle

abnormal muscle fiber morphology ( J:285564 )

• gastrocnemius and quadriceps muscles show abundant accumulations resembling nemaline bodies, with less abundance in the masseter, extensor digitorum longus and diaphragm, and none in soleus or tibialis anterior muscles

• aggregates are predominately found in MHC type IIB (fast, glycolytic) fibers

• nemaline bodies are large and irregular

• males show tubular aggregates in skeletal muscles at 9 months of age comparable to those seen in wild-type males at 18 months of age

• core-like structures are present in the oxidative fibers of tibialis anterior and masseter muscles, and occasionally in the quadriceps; core-like structures do not correspond to areas of nemaline body aggregation and are only present in a subset of fibers

• split myofibers are seen in the quadriceps and extensor digitorum longus

• large intermyofibrillar aggregates of mitochondria are seen in a subpopulation of myofibers of skeletal muscles, with variation in mitochondrial size within the aggregates

decreased skeletal muscle fiber size ( J:285564 )

• all myofibers containing fast MHC (type IIA, IIB, IIA, and/or IIX) fibers are smaller in the EDL

• all myofibers form the soleus muscle are smaller

decreased skeletal muscle fiber diameter ( J:285564 )

increased variability of skeletal muscle fiber size ( J:285564 )

• myofiber size variation is seen in the quadriceps

abnormal skeletal muscle fiber type ratio ( J:285564 )

• in EDL and soleus, the oxidative fiber types (slow MHC I or fast IIA) are more abundant, while there are fewer fast twitch, glycolytic type II fibers

abnormal muscle physiology ( J:285564 )

• tibials anterior muscle myofibers show a 22% lower mean maximum specific force, a 28% slower mean rate of force redevelopment, and an unaffected maximum unloaded shortening velocity and normal thin filament length

impaired skeletal muscle contractility ( J:285564 )

• twitch contraction times are faster in the extensor digitorum longus (EDL) muscles, however no difference in soleus muscle twitch contraction times is seen

• EDL and soleus muscles show a decrease in normalized force at low stimulation frequencies

• the EDL is more susceptible to eccentric contraction-induced muscle damage than wild-type controls when stretched from 120 to 140% of optimal muscle length during eccentric activation

• EDL muscles are stiffer, with EDL transient stretch response 20% greater than in wild-type mice response during 140% of optimal muscle length stretch

• soleus muscle show a 15% decrease in stiffness during 140% of optimal muscle length stretch

behavior/neurological

decreased grip strength ( J:285564 )

♀ • 6 month old females, but not males, show a deficit in muscle force in the grip strength test

decreased locomotor activity ( J:285564 )

♀ • females show decreased performance in daily distance, average speed, and maximum speed at 6 months, but not 3 months, in voluntary running wheels

growth/size/body

decreased body size ( J:285564 )

♀ • females are smaller than controls at 6 months of age

Mouse Models of Human Disease		DO ID	OMIM ID(s)	Ref(s)
nemaline myopathy 2		DOID:0110928	OMIM:256030	J:285564