UW-Madison researchers in collaboration with Medical College of Wisconsin researchers have developed longer lasting botulinum toxin light chain proteins. While the heavy chain of the protein targets the toxin to neuronal cells, the light chain provides the enzymatic activity of the toxin which interrupts neuronal signaling. The researchers developed mRNA constructs that can be transfected into cells to express the light chain enzyme. mRNA constructs needed to be optimized for use in neuronal cells. They were packaged into lipid nanoparticles for cell transfection. The researchers created 5 mRNA constructs for different portions of the light chain from the A1 and A3 subtypes. They transfected these constructs into hiSPC-derive motor neurons. The mRNA constructs encoding the low homology domains from the A1 light chain showed the longest acting activity in cleaving its substrate, SNAP-25. This work serves as proof-of-concept work that botulinum toxin mRNA therapeutics are feasible. The low homology domain from the A1 light chain can be used to impart the longest acting activity.