Generation and characterization of Sema6aΔcyt conditional knockout mice

The axon guidance molecule Semaphorin-6A (SEMA6A) plays a key role during nervous system development. SEMA6A, classically known as a ligand for Plexin-A2 and -A4, is a transmembrane protein that can also elicit signaling via its intracellular domain in vitro . However, the physiological relevance of this reverse signaling route is largely unknown. We generated a new transgenic mouse model, Sema6aΔcytfl/fl , in which the cytosolic part of SEMA6A can be conditionally removed using Cre -recombination. Upon Sema6aΔcyt mutation, SEMA6A can only act as a ligand and reverse signaling is perturbed. Germline deletion of the SEMA6A intracellular part results in developmental defects in axon pathfinding and neuron migration that partially phenocopy defects observed in full Sema6a knockout mice. These defects include disorganization of the anterior commissure, piriform cortex, lateral olfactory tract, thalamocortical and corticospinal white matter tracts, and defected neuron migration in the neocortex and cerebellum. Intriguingly, the hippocampal malformation described in Sema6a full knockout mice was not reproduced, suggesting a specific role for SEMA6A-Plexin-A2/A4 forward signaling in hippocampal development. Our results indicate that the intracellular domain of SEMA6A is essential for proper axon targeting and neuron migration, and provide the first proof of a SEMA6A reverse signaling pathway in vivo . ### Competing Interest Statement The authors have declared no competing interest.