Myosin is a family of proteins that plays a crucial role in generating force and motion by interacting with actin filaments in skeletal muscle. Myosin molecules notably contain heavy chain (MyHC) isoforms that have different functional capabilities. Mutations in one of its isoforms, MyHC I/β (encoded by the
MYH7 gene) have been reported in humans, associated with muscle weakness and have led to two main distinct skeletal muscle diseases, Laing Distal Myopathy (LDM) and Myosin Storage Myopathy (MSM). The pathophysiological mechanisms by which subtle amino acid changes in the LMM region of MyHC I/β molecules leading to such variable skeletal muscle phenotypes in LDM and MSM patients remain poorly understood. Using a wide range of human
MYH7 patient muscle biopsy samples, investigation of primary biophysical defects in the presence of defective MyHC I/β molecules including myosin filament length has revealed no change but rather a shift in myosin head positioning into a disordered relaxed state (DRX). On the road to generating a zebrafish LDM and MSM disease model, several genes were identified to be orthologous to human
MYH7. Amongst orthologous genes,
smyhc1 was targeted for genome editing using CRISPR/Cas9 to generate a loss of function model. Loss of
smyhc1 led to early developmental defects, however, continued to grow to adulthood with no observable muscle defects.
Smyhc1 null zebrafish are replaced and compensated by
smyhc2 and
smyhc3 in adult zebrafish. Work ongoing to generate large deletion of
smyhc locus to understand the role of slow MyHC in sarcomere assembly during early developmental stages through to adulthood. It is concluded that in the presence of LDM mutations in the MyBP-C binding domain, myosin heads in the SRX state are destabilised, and zebrafish smyhc1 is orthologous to human
MYH7 but only functions during the early stages of development. Continued work to generate knockout of
smyhc locus may describe the function of
smyhc2 and
smyhc3 in later stages of development in the quest to model the progressive phenotype in LDM and MSM patients.
| Date of Award | 1 Sept 2022 |
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| Original language | English |
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| Awarding Institution | |
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| Supervisor | Julien Ochala (Supervisor) & Simon Hughes (Supervisor) |
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