Targeted insertion of the Cre-recombinase gene at the phenylethanolamine n-methyltransferase locus: A new model for studying the developmental distribution of adrenergic cells

To evaluate the developmental distribution of adrenergic cells in vivo, we inserted the Cre-recombinase gene into the locus encoding for the epinephrine biosynthetic enzyme phenylethanolamine n-methyltransferase (Pnmt) and crossed these Pnmt-Cre mice with ROSA26 reporter (R26R) mice to activate LacZ (encoding β-galactosidase) expression in cells that were selectively derived from the adrenergic lineage. Our data show the following: (1) Insertion of Cre-recombinase into the Pnmt locus created a functional knockout of Pnmt expression with concomitant loss of epinephrine in homozygous Pnmt ^Cre/Cre mice; (2) Despite the reduction in Pnmt expression and epinephrine production in Pnmt^Cre/Cre mice, these mice were viable and fertile, with no apparent developmental defects; (3) When crossed with R26R mice, Pnmt-Cre activation of LacZ expression faithfully recapitulated Pnmt expression in vivo; and (4) LacZ expression was activated in substantial numbers of pacemaking, conduction, and working cardiomyocytes.