GDNF family receptors in the embryonic and postnatal rat heart and reducedcholinergic innervation in mice hearts lacking Ret or GFR alpha 2

Members of the GDNF family, which are important during peripheral nervous s ystem development and kidney organogenesis, signal via Ret and GFR alpha re ceptors. Here we have studied their possible role in heart development. Gfr a1 was expressed in the endocardial cushion mesenchyme at E12 and later, in the developing and mature valves, and in the walls of the aorta and the pu lmonary trunk. Gfra2 was expressed in the outer layers of the aorta and pul monary trunk and in the valves at E18-P60. Endocardial cells showed moderat e Gfra2 mRNA and protein expression between E12 and E15. Gfra3 mRNA was det ected, mainly postnatally, in scattered cells of the atria and the great ve ssels. In embryonic and postnatal rat cardiac ganglia, Ret and Gfra2 transc ripts were seen in the neurons, whereas Gfra1 and Gfra3 mRNA were preferent ially found in non-neuronal cells within the ganglia. GFR alpha 2 immunorea ctivity was seen in both cardiac ganglion neurons and their nerve fibers. T here were no obvious non-neuronal defects in hearts of Ret-, GFR alpha 1-, or GFR alpha 2-deficient mice, suggesting that these receptors are not esse ntial for gross cardiac development. However, E18 Ret-deficient mice exhibi ted a reduced volume of cardiac ganglia and cholinergic innervation of the ventricular conduction system. Moreover, adult Gfra2(-/-) mice showed reduc ed cholinergic innervation by 40% in their ventricles and by 60% in the ven tricular conduction system. These findings indicate that GFR alpha 2/Ret si gnaling is required for normal cholinergic innervation of heart. (C) 2000 W iley-Liss, Inc.