FEZ1 (fasciculation and elongation protein zeta 1) is a multifunctional kinesin-1 adaptor protein with critical roles in neuronal development and intracellular transport. Primary function: FEZ1 regulates axonal outgrowth and cargo transport along microtubules, particularly for mitochondria and synaptic proteins 1. The protein contains disordered regions and functions as a dimer 2, with phosphorylation at key sites modulating its protein-binding interactions 2. Mechanism: FEZ1 operates through multiple pathways—it mediates nuclear translocation of viral capsids 34, regulates heat shock protein HSPA8 localization and innate immune signaling 5, and controls neuroprogenitor specification during cortical development 6. FEZ1 is highly expressed in developing forebrain neurons and oligodendroglia, with expression patterns varying by brain region and developmental stage 78. Disease relevance: FEZ1 mutations are associated with schizophrenia and Jacobsen syndrome 61. Jacobsen syndrome patients exhibit motor impairments correlating with FEZ1 deletion-induced defects in motor neuron development and synaptic protein transport 1. In schizophrenia, dysregulation of FEZ1 through chr11 modifications and RNA-binding proteins impairs oligodendroglia maturation 8. Clinical significance: FEZ1 emerges as a hub protein integrating neuronal development, viral trafficking, and innate immunity—potential therapeutic target for neurodevelopmental and infectious diseases.