Ankyrin-2 (Ank2) and neurofilament heavy polypeptide (Nefh) are additional cytoskeletal proteins that play a role in proper formation, stability, and functioning of synapses (Yang et al. 2019; Koch et al. 2008; Galiano et al. 2012; Yuan et al. 2015). Our phosphoproteomics analysis revealed twelve significantly different ankyrin-2 phosphopeptides with many peptides in the top 20 differentially expressed phosphopeptides between lines. In drosophila, casein kinase 2 targets ankyrin-2 to maintain synapse stability suggesting certain phosphomodifications of ankyrin-2 may be important to preserve synaptic terminal integrity (Bulat et al. 2014). Elevated ankyrin-2 may also increase spontaneous excitatory postsynaptic current frequency (without affecting inhibitory currents) in mouse hippocampal neurons, creating an excitation/inhibition imbalance (Lippi et al. 2016). If ankyrin-2 functions similarly in the mouse DS, the differential phosphomodifications could contribute to increased excitation and glutamatergic activity demonstrated in HAP MSNs relative to LAP mice. Similarly, fifteen different neurofilament heavy polypeptide (NFH) phosphopeptides were found to be differentially expressed between groups. NFH is a known target of numerous protein kinases, and these phosphorylation events regulate the interaction between different neurofilament subunits and other cytoskeletal
