BoNT/B showed reduced potency and toxicity on Syt2^M3 KI mice.

A-C. BoNT/A (5 pg) was injected into the right gastrocnemius muscle of mice and muscle paralysis was scored by monitoring the degree of toe spreading in startle responses (DAS assays). BoNT/A showed the same levels of potency in inducing local muscle paralysis in DAS assays in WT, Syt1^M3, Syt2^M3, and Syt1/Syt2^M3 double KI mice. Representative pictures of toe spreading are shown in A. The maximal DAS scores are plotted in B, and the mean daily DAS scores three days after toxin injection are plotted in C. Data represent mean +/- SEM. ns = not significant. D-F. BoNT/B showed reduced potency in inducing local paralysis and systemic toxicity in DAS assays on Syt2^M3 KI and Syt1/Syt2^M3 KI mice compared with WT and Syt1^M3 KI mice. Representative images of toe spreading in DAS assays with the indicated doses are shown in D, mean DAS scores with different toxin doses are plotted in E, and the survival rates with the indicated toxin doses are plotted in F. The BoNT/B doses that resulted in moribund start at 4.25 pg for WT, 3.25 pg for Syt1^M3, 125 pg for Syt2^M3, and 200 pg for Syt1/Syt2^M3 mice. Panels A, B, C–WT and Syt1^M3 mice, n = 3, Syt2^M3 and Syt1/Syt2^M3 mice, n = 4. Panels D, E–all groups that received BoNT/B injection, n = 5. Except for the following groups: WT 5.5 pg BoNT/B (n = 4); Syt2^M3 100 pg BoNT/B (n = 10); Syt2^M3 150 pg BoNT/B (n = 3); Syt1/Syt2^M3 100 pg BoNT/B (n = 6); Syt1/Syt2^M3 150 pg BoNT/B (n = 6). Panel F–these numbers are from the same dataset as panels D, E.