JOURACA_SP_2017

C. elegans thick filaments assemble with a
decapitated myosin A
Hallea Ward
Striated muscle makes up about 40-70% of animal
muscle mass, and around 40% of that consists
of contractile filaments. Actin (thin) and
myosin (thick) filaments, in striated muscle, assemble
together in such a way that they slide
past one another to generate contractile force
and shortening. Thick filaments in the body wall
muscle of the nematode Caenorhabditis elegans
have a unique bipolar structure that is composed
of myosin A (myoA) and myosin B (myoB)
isoforms. These two isoforms are located in distinct
regions of the thick filament and are encoded
by different genes, thus making it possible to
investigate muscle assembly by genetically altering
one isoform while still keeping the other
isoform functioning appropriately. We used
CRISPR-Cas9 homologous gene editing to
make a transgenic strain that expresses the myoA
head and tail domains as separate polypeptides
to create a large bare zone in the center of
the thick filament. By using fluorescence microscopy,
we found that the myoA tail domain
localizes to thick filaments in all expected muscle
types including body wall muscle and that
the sarcomere organization is normal. Surprisingly,
viability, development, growth, and locomotion
of the transgenic and wildtype worms
are indistinguishable from each other under normal
laboratory conditions. Our results show that
the thick filament assembly can occur when the
myoA head is separated from the myoA tail. We
propose an assembly model where the myoA
tail is capable of nucleating thick filaments independent
of thin filament interactions.
Department of Biology
Mentor: Dr. Ryan Littlefield
Department of Biology
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