Identification and characterization of Slitrk, a novel neuronal transmembrane protein family controlling neurite outgrowth.

The Slitrk family consists of six structurally related transmembrane proteins (Slitrk1-6) in the mouse. In the extracellular region, they share two conserved leucine-rich repeat domains that have a significant homology to a secreted axonal growth-controlling protein, Slit. These proteins also have a homology to trk neurotrophin receptors in their intracellular domains, sharing a conserved tyrosine residue. Expression of Slitrk is highly restricted to neural tissues, but varies within the family. More specifically, Slitrk1 expression is in the mature neurons, whereas Slitrk2 is strongly expressed in the ventricular layer, and Slitrk6 shows compartmentalized expression in diencephalon. Over-expressed Slitrk1 induced unipolar neurites in cultured neuronal cells, whereas Slitrk2 and other Slitrk proteins inhibited neurite outgrowth. Deletion analysis showed that the functional difference between Slitrk1 and Slitrk2 lies in their intracellular domains, which are conserved in Slitrk2-6, but not in Slitrk1. These results suggest that the Slitrk proteins are the neuronal components that control the neurite outgrowth.