Updated project metadata. Neurons express Phactr1 at high level (Allen et al., 2004), and Phactr1 mutations are associated with morphological and functional developmental defects in cortical neurons (Hamada et al., 2018). To identify targets of the Phactr1/PP1 phosphatase holoenzyme, we cultured hippocampal and cortical neurons from wildtype and Phactr1-null animals, treated them either with Latrunculin B or Cytochalasin D to inhibit or activate formation of the Phactr1/PP1 complex (Wiezlak et al., 2012), and analysed phosphorylation profiles using TMT phosphoproteomics. Among over 9000 phosphorylation sites quantified, we found numerous phosphorylation sites that differed significantly in their response to these stimuli in wildtype as opposed to Phactr1-null neurons.