Synaptopodin KO rat for assessing the dendritic spine apparatus and axonal cisternal organelle in synaptic plasticity, development, and behavior

The actin-binding protein synaptopodin (Synpo) regulates the cytoskeleton and intracellular Ca2+ and is important for long-term potentiation (LTP) and learning. The inconsistent onset age for LTP in mice makes their Synpo knockout (KO) a suboptimal developmental model. Hence, we generated Synpo KO rats using CRISPR-Cas9. Synpo KO rats are viable with reduced body weight and bone length after postnatal days (P)35-P45. Their basal kidney function is normal. 3D reconstruction from electron microscopy reveals the absence of the Synpo-dependent dendritic spine apparatus and cisternal organelles in the axon initial segment (AIS), which may contribute to reduced LTP in the KO rat. Inhibitory synapses in the wild-type AIS appear preferentially clustered near cisternal organelles - a pattern disrupted in the KO, where synapses appear more uniformly distributed. The consistent developmental profile of LTP in the rat makes this KO a robust model to assess Synpo function in development, synaptic plasticity, and behavior.