Investigating how Mylpf-regulated sarcomere formation influences limb skeletal development
In arthrogryposis, babies are born with at least two limbs with hand or foot showing contractures; it most
commonly manifests as clubfoot, and it is found in roughly 1 in 4000 live births. Arthrogryposis causes impaired
movement and can require many surgeries through a lifetime to correct. The disease is characterized by
skeletal joint defects, but it is caused by impaired muscle movement in utero. We recently found that the
muscle-expressed gene Mylpf is vital not only to normal actin movement, but also for muscle fiber integrity and
that variants in human MYLPF cause Distal Arthrogryposis Type 1 (DA1). Mylpf protein binds to the myosin
heavy chain near head region which moves actin during muscle contraction. We discovered that zebrafish
mylpfa mutant larvae display a phenotype consistent with DA1, including impaired myosin activity, reduced
muscle force overall, and complete fin paralysis. Surprisingly, we find that Mylpf function is needed not only for
normal contraction, but also for the assembly of actin and myosin into the fundamental unit of muscle, called
sarcomeres. In unpublished work we find that sarcomeres form poorly in mylpfa mutants, lacking one of two
Mylpf genes, and are completely absent in mylpfa;mylpfb double mutants, which lack all Mylpf function. We
hypothesize that Mylpf function prevents distal arthrogryposis by promoting association of sarcomeric
components during the critical window of embryonic development when limb joints are forming. To test this
hypothesis, we will (Aim 1) investigate the role of Mylpf in sarcomere assembly, (Aim 2a) investigate how the
human MYLPF gene variants cause this musculo-skeletal disease, and (Aim 2b) when the skeletal defects can
be corrected.
