Key result
A titin splicing defect mutation in rats eliminated the developmental reduction in titin size, causing titins in skeletal muscles to remain large in adults due to repressed alternative splicing.
An autosomal dominant mutation in rats represses alternative splicing of titin mRNA, preventing the normal developmental reduction in titin size in skeletal muscles.
Titin size maintenance may affect skeletal muscle properties; leaves open relevance of splicing defects to human myopathies.
Titin is a giant protein with multiple functions in cardiac and skeletal muscles. Rat cardiac titin undergoes developmental isoform transition from the neonatal 3.7 MDa N2BA isoform to primarily the adult 2.97 MDa N2B isoform. An autosomal dominant mutation dramatically altered this transformation. Titins from eight skeletal muscles: Tibialis Anterior (TA), Longissimus Dorsi (LD) and Gastrocnemius (GA), Extensor Digitorum Longus (ED), Soleus (SO), Psoas (PS), Extensor Oblique (EO), and Diaphram (DI) were characterized in wild type and in homozygous mutant (Hm) rats with a titin splicing defect. Results showed that the developmental reduction in titin size is eliminated in the mutant rat so that the titins in all investigated skeletal muscles remain large in the adult. The alternative splicing of titin mRNA was found repressed by this mutation, a result consistent with the large titin isoform in the mutant. The developmental pattern of titin mRNA alternative splicing differs between heart and skeletal muscles. The retention of intron 49 reveals a possible mechanism for the absence of the N2B unique region in the expressed titin protein of skeletal muscle.
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Li et al. (2011) studied Titin splicing defect. Titin splicing defect mutation vs. Wild type was evaluated on Titin protein isoform size and alternative splicing. A titin splicing defect mutation in rats eliminated the developmental reduction in titin size, causing titins in skeletal muscles to remain large in adults due to repressed alternative splicing.
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