MAPT and tauopathy: Taken together with IHC data from rTg4510 mouse and human tauopathy brains, lack of detectable signal in Mapt−/− brain sections demonstrated selectivity to phosphorylated Tau for all antibodies, with the notable exception of the pSer199 antibody, which cross-reacted with a nuclear phospho-epitope present in CA1 pyramidal neurons, the levels of which appeared to increase in Mapt−/− neurons compared to wildtype neurons (Supp.