E10.5 embryos were fixed in 4% PFA in PBS at 4°C, rinsed in PBS, then permeabilized in PBS with 0.5% Triton X-100 for 24hrs at 4°C. Neurofilament immunodetection was performed as previously described (Ray et al., 2020 (link)). Primary anti-neurofilament antibody (DHSB, 2H3) was used at a 1:20 dilution and anti-mouse HRP-conjugated secondary antibody (Jackson ImmunoResearch, 115-035-003) was used at 1:1000 dilution. Signal was developed using the ImmPACT DAB Substrate Kit (Vector Laboratories, SK-4105). Photographs were taken using a Nikon SMZ-U dissecting scope fitted with a Jenoptik ProgRes C5 camera.