  The 1-loop renormalization group equations for the minimal Z' models
encompassing a type-I seesaw mechanism are studied in the light of the 125 GeV
Higgs boson discovery. This model is taken as a benchmark for the general case
of singlet extensions of the standard model. The most important result is that
negative scalar mixing angles are favoured with respect to positive values.
Further, a minimum value for the latter exists, as well as a maximum value for
the masses of the heavy neutrinos, depending on the vacuum expectation value of
the singlet scalar.
