A Genetic Strategy for the Analysis of Individual Axon Morphologies in cGMP Signalling Mutant Mice

One of the many physiological functions of cyclic guanosine 3′,5′ monophosphate (cGMP) signalling is the regulation of a specific mode of axonal branching. The bifurcation of axons from dorsal root ganglion (DRG) neurons at the dorsal root entry zone of the embryonic spinal cord is triggered by a cGMP �signalling pathway comprising the ligand C-type natriuretic peptide (CNP), the cGMP-producing natriuretic peptide receptor 2 (Npr2), and the cGMP-dependent protein kinase Iα (cGKIα). Absence of any of these components causes a loss of bifurcation and sensory axons instead only turn in either a rostral or a caudal direction. In this chapter we describe a genetic strategy to study the impact of cGMP signalling on the arborization of individual DRG neurons in mice. Expression of an alkaline phosphatase (AP) reporter is selectively induced in Npr2-positive DRG neurons by tamoxifen-dependent activation of a Cre �recombinase under the control of the Npr2 promoter. This approach might also be employed for the analysis of axonal branching in neuronal subsets expressing Npr2 elsewhere in the nervous system.