A transgenic mouse line to study axon initial segments and nodes of Ranvier in living neurons in vitro and in vivo

Christian Thome1, Krabulut Seda2, Claudio Acuna Goycolea1, Elisa D'Este3, Stella Soyka1, Andrew Nelson4, Christian Schultz2, Vann Bennett5, Paul Jenkins1, Maren Engelhardt2

1 Heidelberg University
2 Heidelberg University, Medical Faculty Mannheim
3 MPI for Medical Research
4 University of Michigan
5 Duke University

The axon initial segment (AIS) is the cellular compartment where most neurons generate their primary output signal: the action potential. Saltatory transmission of action potentials is enabled by nodes of Ranvier, which share structural features with the AIS such as an Ankyrin-G scaffold and the clustering of voltage-gated sodium and potassium channels. Recent techniques to study the AIS and its remodeling have been limited in their application in acute living tissue. Here, we present and characterize a transgenic mouse line, in which AIS and nodes of Ranvier are intrinsically labeled with a genetically encoded fluorophore. In this model, a modified sequence generates an Ankyrin-G-GFP fusion protein that is activated by Cre recombinase and only visualizes endogenous Ankyrin-G. The label is thus specific to subsets of neurons at defined time-points in the living animal, depending on which Cre-line is selected as a cross or which virus is injected.