Novel Role for Perinatal Myosin in Skeletal Muscle Development
Location
Philadelphia Campus
Start Date
7-5-2014 1:00 PM
Description
Trismus-pseudcamptodactyly (TPC) is a rare, hereditary muscle syndrome that is characterized by an inability to open the mouth fully (trismus) and involuntary contractures of interphalangeal joints (pseudocamptodactyly). These jaw, hand and foot contractures complicate dental care, feeding during infancy, intubation for anesthesia, walking and also impair manual dexterity. Occupational and social disabilities occur as a result of these complications and these contractures often require surgical correction. Our lab sought to identify the underlying molecular genetic cause for TPC through mutational analysis of its affected family members. Sequence analysis revealed an Arg674Gln missense mutation (R674Q) in the MYH8 gene encoding the perinatal isoform of myosin heavy chain, MyHCpn. The Arg674 residue is highly conserved among the myosin heavy chain family of contractile proteins and it localizes to the actin-binding domain of the perinatal myosin head close to the ATP-binding site. To define the role of MyHCpn in mammalian development, we established a genetically engineered mouse line carrying the orthologous R674Q mutant Myh8 allele. Using Cre-lox technology to express the mutant isoform of Myh8 in the mouse genome, we mated our Myh8R674Qneo/+ mice with the EIIa-Cre ubiquitous driver mice to generate Myh8 R674Q/+;EIIa-Cre mice that are heterozygous for mutant Myh8. Newborn Myh8R674Q/+;EIIa-Cre mice die within minutes after birth due to respiratory failure. Gross examination of these mice at embryonic day (E) 18.5 revealed smaller embryos with bulging abdomens compared to wildtype control embryos. Histological examination of skeletal muscles from E18.5 Myh8R674Q/+;EIIa-Cre embryos revealed variability in muscle fiber size, signs of apoptosis and increased muscle degeneration/regeneration. Electron microscopic images of skeletal muscles showed enlarged mitochondria, focal absence of myofibrils, loosely arrayed fiber bundles and regional Z-line irregularities within the sarcomeres. We also observed the presence of nemaline deposits indicative of nemaline myopathy. These findings suggest a novel and crucial role for MyHCpn in skeletal muscle development.
Novel Role for Perinatal Myosin in Skeletal Muscle Development
Philadelphia Campus
Trismus-pseudcamptodactyly (TPC) is a rare, hereditary muscle syndrome that is characterized by an inability to open the mouth fully (trismus) and involuntary contractures of interphalangeal joints (pseudocamptodactyly). These jaw, hand and foot contractures complicate dental care, feeding during infancy, intubation for anesthesia, walking and also impair manual dexterity. Occupational and social disabilities occur as a result of these complications and these contractures often require surgical correction. Our lab sought to identify the underlying molecular genetic cause for TPC through mutational analysis of its affected family members. Sequence analysis revealed an Arg674Gln missense mutation (R674Q) in the MYH8 gene encoding the perinatal isoform of myosin heavy chain, MyHCpn. The Arg674 residue is highly conserved among the myosin heavy chain family of contractile proteins and it localizes to the actin-binding domain of the perinatal myosin head close to the ATP-binding site. To define the role of MyHCpn in mammalian development, we established a genetically engineered mouse line carrying the orthologous R674Q mutant Myh8 allele. Using Cre-lox technology to express the mutant isoform of Myh8 in the mouse genome, we mated our Myh8R674Qneo/+ mice with the EIIa-Cre ubiquitous driver mice to generate Myh8 R674Q/+;EIIa-Cre mice that are heterozygous for mutant Myh8. Newborn Myh8R674Q/+;EIIa-Cre mice die within minutes after birth due to respiratory failure. Gross examination of these mice at embryonic day (E) 18.5 revealed smaller embryos with bulging abdomens compared to wildtype control embryos. Histological examination of skeletal muscles from E18.5 Myh8R674Q/+;EIIa-Cre embryos revealed variability in muscle fiber size, signs of apoptosis and increased muscle degeneration/regeneration. Electron microscopic images of skeletal muscles showed enlarged mitochondria, focal absence of myofibrils, loosely arrayed fiber bundles and regional Z-line irregularities within the sarcomeres. We also observed the presence of nemaline deposits indicative of nemaline myopathy. These findings suggest a novel and crucial role for MyHCpn in skeletal muscle development.