Phosphorylation of Dpsyl2 (CRMP2) and Dpsyl3 (CRMP4) is required for positioning of caudal primary motor neurons in the zebrafish spinal cord

Dpysls (CRMPs) that were initially identified as mediator proteins of Semaphorin3a (Sem3a) signaling are involved in neuronal polarity and axon elongation in cultured neurons. Previous studies have shown that knockdown of neuropilin1a, one of the sem3a receptors, exhibited ectopic primary motor neurons (PMNs) outside of the spinal cord in zebrafish. However, downstream molecules of sem3a signaling involved in the positioning of motor neurons are largely unknown. Here, we addressed the role of Dpysl2 (CRMP2) and Dpysl3 (CRMP4) in the positioning of PMNs in the zebrafish spinal cord. We found that the knockdown of dpysls by antisense morpholino oligonucleotides (AMO) causes abnormal positioning of caudal primary (CaP) motor neurons outside the spinal cord. The knockdown of cdk5 and dyrk2 by AMO also caused similar phenotype in the positioning of CaP motor neurons, and this phenotype was rescued by co-injection of phosphorylation-mimic type dpysl2 mRNA. These results suggest that the phosphorylation of Dpysl2 and Dpysl3 by Cdk5 and Dyrk2 is required for correct positioning of CaP motor neurons in the zebrafish spinal cord.