Axonal isoforms of myosin-I

• Published in: Biochemical and biophysical research communications Vol. 330; no. 3; pp. 857 - 864
• Main Authors: Lund, Linda M., Machado, Victor M., McQuarrie, Irvine G.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 13-05-2005
• Subjects: Animals; Axonal Transport; Axons; Axons - metabolism; Blotting, Western; Immunohistochemistry; In Situ Hybridization; Intracellular transport; Male; Microfilaments; Motor Neurons - cytology; Motor Neurons - metabolism; Myosin I; Myosin Type I - genetics; Myosin Type I - metabolism; Protein Isoforms - genetics; Protein Isoforms - metabolism; Rats; Rats, Sprague-Dawley; Sciatic motor neurons; Sciatic motor neurons; Axons; Intracellular transport; Myosin I; Microfilaments
• ISSN: 0006-291X; 1090-2104
• DOI: 10.1016/j.bbrc.2005.02.187

We have examined spinal motor neurons in Sprague–Dawley rats to further characterize a mechanoenzyme, myosin-Iγ (
myr4), which is found in high concentration during axon tract formation in neonates. We raised an antibody to
myr4 and made riboprobes for in situ hybridization.
Myr4 mRNA was abundant in spinal cord motor neurons (particularly during axon regrowth). Nerves undergoing Wallerian degeneration (from a crush 7 days earlier) showed anti-
myr4 labeling of the axolemma and SER—after microtubules, neurofilaments, and F-actin had already been degraded—which is consistent with a described lipid-binding domain in the tail region of myosin-Is. Newly synthesized
myr4 was carried in axons by the slow component (SC) of axonal transport at 1–8
mm/day, whereas, none was carried by the fast component (FC). We conclude that SC delivers
myr4 to the cytoplasmic surfaces of stationary axonal membranes (SER and axolemma). This positioning would anchor the tail domain of
myr4 and leave the catalytic head domain free to interact with F-actin.