zfNLRR, a novel leucine-rich repeat protein is preferentially expressed during regeneration in zebrafish

zfNLRR is a novel transmembrane protein that is most prominently expressed during regeneration of the zebrafish central nervous system. Retinal gangli on cells and descending spinal cord neurons strongly increase zfNLRR mRNA l evels after axotomy in the adult. In contrast, during development expressio n is hardly detectable and is restricted to a few sensory systems. In the a dult brain, zfNLRR mRNA is found at low levels in several motor and premoto r systems. Sequence analysis reveals that zfNLRR contains in its extracellu lar region 12 leucine-rich repeats, 1 immunoglobulin-like domain and 1 fibr onectin type III-like domain. The same protein binding motifs were identifi ed in transmembrane proteins from frog, mouse, and human. Together, they co nstitute a novel family of vertebrate neuronal leucine-rich repeat proteins . Three distinct isoforms are identified so far. On the basis of its struct ural features and expression pattern, we propose that zfNLRR functions as a neuronal-specific adhesion molecule or soluble ligand binding receptor, pr imarily during restoration of the nervous system after injury.