The function of the scaffolding proteins Fez1 and Fez2 in polarized transport and neuronal migration

• Applicant: Professor Dr. Andreas Püschel
• Subject Area: Developmental Neurobiology ; Developmental Biology
• Term: from 2015 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 271137065

The establishment and maintenance of the highly polarized architecture of neurons is essential for the formation and functionality of neuronal networks and depends on the selective transport of specific cargos into axons and dendrites. Axon formation is preceded by the polarization of transport processes and an increased transport of vesicles and mitochondria into the future axon. Scaffolding proteins that link molecular motors and their cargo are important factors that connect signaling pathways and transport processes. However, the molecular mechanisms that regulate the association of cargo and molecular motors and direct them to a specific cellular location are still poorly understood. One of the molecular motors that mediate the transport of vesicles and mitochondria is kinesin-1. Kinesin-1 assumes an autoinhibited conformation in the absence of cargo. Kinesin-1 is activated by the binding of the scaffolding proteins Jnk interacting protein 1 (Jip1) and Fasciculation elongation zeta 1 (Fez1). Knockdown of Fez1 in cultured hippocampal neurons affects axon formation and the transport of mitochondria. Surprisingly, Fez1 knockout mice are viable and do not show defects in the development of the nervous system. The absence of major developmental defects is attributed to a possible redundancy with Fez2 but the physiological function of Fez2 has not been explored so far. Transport processes are important not only during axon formation but also during neuronal migration. Our analysis of conditional Rap1a;Rap1b double knockout mice showed that Rap1 GTPases are essential for the polarization of radial glia and neurons. One function of Rap1 GTPases is to direct cadherin trafficking in migrating neurons. We have therefore begun to analyze the function of Fez1 and Fez2 to understand the molecular mechanisms underlying polarized transport. Our preliminary experiments show that Fez2 localizes to mitochondria as already reported for Fez1. Knockdown of Fez2 in cultured hippocampal neurons results in defects in axon formation. In addition, we observed neuronal migration defects in cortical slice cultures after ex vivo electroporation of a Fez2 knockdown construct. In this project, we will investigate the function of Fez proteins in the transport of mitochondria and specific vesicles and its role in neuronal migration. We will use primary cultures of dissociated hippocampal neurons, live cell imaging of neuronal migration in slice preparations, and Fez2 knockout mice for these experiments.

• DFG Programme: Research Grants