While not tested here, tau fibrils isolated from the PS19 mouse model (Yoshiyama et al., 2007) also differ significantly from the 4R tauopathy human patient samples (Schweighauser et al., 2023), suggesting that the tau strain in these mice is also likely to exhibit a unique biological profile in our Tau4RD (244–380)-YFP reporter lines. Here, MAPT is linked to tauopathy.