Collapsin response mediator proteins (CRMPs) are intracellular proteins that mediate signals for several extracellular molecules, such as Semaphorin3A and neurotrophins. The phosphorylation of CRMP1 and CRMP2 by Cdk5 at Ser522 is involved in axonal guidance and spine development. Here, we found that the Ser522-phosphorylated CRMP1 and/or CRMP2 are enriched in the dendrites of cultured cortical neurons and P7 cortical section. To determine the physiological role of CRMPs in dendritic development, we generated CRMP2 knock-in mutant mice (crmp2ki/ki) in which the Ser residue at 522 was replaced with Ala. Strikingly, the cortical basal dendrites of double mutant crmp2ki/ki and crmp1_/_ mice exhibited severe abnormal dendritic patterning, which we defined as "curling phenotype." These findings demonstrate that the function of CRMP1 and CRMP2 synergistically control dendritic projection, and the phosphorylation of CRMP2 at Ser522 is essential for proper dendritic field organization in vivo.
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