MYH3-associated Distal Arthrogryposis Zebrafish Model is Normalized with Para-aminoblebbistatin

Distal arthrogryposis (DA) is group of syndromes characterized by congenital joint contractures. Treatment development is hindered by the lack of vertebrate models. Here, we describe a zebrafish model in which a common MYH3 missense mutation (R672H) was introduced into the orthologous zebrafish gene smyhc1 (slow myosin heavy chain 1) (R673H). We simultaneously created a smyhc1 null allele (smyhc1 ), which allowed us to compare the effects of both mutant alleles on muscle and bone development, and model the closely related disorder, spondylocarpotarsal synostosis syndrome. Heterozygous smyhc1 embryos developed notochord kinks that progressed to scoliosis with vertebral fusions; motor deficits accompanied the disorganized and shortened slow-twitch skeletal muscle myofibers. Increased dosage of the mutant allele in both homozygous smyhc1 and transheterozygous smyhc1 embryos exacerbated the notochord and muscle abnormalities, causing early lethality. Treatment of smyhc1 embryos with the myosin ATPase inhibitor, para-aminoblebbistatin, which decreases actin-myosin affinity, normalized the notochord phenotype. Our zebrafish model of MYH3-associated DA2A provides insight into pathogenic mechanisms and suggests a beneficial therapeutic role for myosin inhibitors in treating disabling contractures.