<p>Abstract</p> <p>Background</p> <p>Capricious is a <it>Drosophila </it>adhesion molecule that regulates specific targeting of a subset of motor neurons to their muscle target. We set out to identify whether one of its vertebrate homologues, Lrrn2, might play an analogous role in the chick.</p> <p>Results</p> <p>We have shown that <it>Lrrn2 </it>is expressed from early development in the prospective rhombomere 4 (r4) of the chick hindbrain. Subsequently, its expression in the hindbrain becomes restricted to a specific group of motor neurons, the branchiomotor neurons of r4, and their pre-muscle target, the second branchial arch (BA2), along with other sites outside the hindbrain. Misexpression of the signalling molecule Sonic hedgehog (Shh) via <it>in ovo </it>electroporation results in upregulation of <it>Lrrn2 </it>exclusively in r4, while the combined expression of Hoxb1 and Shh is sufficient to induce ectopic <it>Lrrn2 </it>in r1/2. Misexpression of Lrrn2 in r2/3 results in axonal rerouting from the r2 exit point to the r4 exit point and BA2, suggesting a direct role in motor axon guidance.</p> <p>Conclusion</p> <p>Lrrn2 acts downstream of Hoxb1 and plays a role in the selective targeting of r4 motor neurons to BA2.</p
