During development, neurons must extend processes and make connections with their appropriate targets. This process is dependent on multiple molecular and cellular mechanisms, and if disrupted, neurodevelopmental disorders can result. We previously demonstrated that Receptor for activated C kinase (RACK1), a ribosomal scaffolding protein, regulates the adhesion and motility of developing neurons through its regulation of point contacts, adhesion points located in the tips of pathfinding axons. Furthemore, RACK1 regulates the local translation of β-actin mRNA, which is necessary for appropriate axon guidance. However, RACK1 has multiple signaling and ribosomal functions, and how the ribosomal binding function of RACK1 contributes to neural development is unknown, Thus, we specifically investigated the ribosomal binding function of RACK1 in point contact formation, axonal outgrowth, and local translation. We overexpressed RACK1-WT, RACK1-DE (a mutant form of RACK1 that cannot bind ribosomes) or a control construct in embryonic mouse cortical neurons. Immunocytochemistry was performed, followed by quantification of point contact formation, axon outgrowth, and local translation of β-actin. Overexpression of RACK1-DE inhibited BDNF-induced point contact formation, and also led to a significant decrease in axonal outgrowth. We are currently examining whether �-actin protein levels decrease following overexpression of RACK1-DE; this is expected because RACK1 mediates the local translation of �-actin. Together, these experiments show that local translation mediated by RACK1 regulates adhesion and axon outgrowth in the developing nervous system. We previously identified aberrant expression of RACK1 in Down syndrome, and thus these results have implications for the pathogenesis of this neurodevelopmental disorder.
Dr. Kristy Welshhans
Mrs. Leah Kershner
Receptor for activated C kinase (RACK1) is known to regulate local translation of β-actin mRNA and point contact formation, which are necessary for neural development. The contribution of the ribosomal binding function of RACK1 to neural development, however, is unclear. We investigated the role of this function in point contact formation, axonal outgrowth, and local translation. RACK1-WT, RACK1-DE (a mutant form of RACK1 that cannot bind ribosomes) or a control construct was overexpressed in embryonic mouse neurons. Immunocytochemistry was used to quantify each experiment. Overexpression of RACK1-DE blocked BDNF-induced point contact formation and decreased axonal outgrowth. Thus, the ribosomal binding function of RACK1 regulates adhesiveness and axonal outgrowth in the developing nervous system and its aberrant expression could contribute to the pathogenesis of neurodevelopmental disorders.