Component of E3 ubiquitin ligase complexes. Required for normal neuromuscular synaptogenesis, axon pathfinding and neuronal migration. Plays a role in the regulation of neurotransmission at mature neurons (By similarity). May control synaptic activity by controlling UNC13A via ubiquitin dependent pathway. Specifically recognizes TP73, promoting its ubiquitination and degradation (By similarity). Protein modification; protein ubiquitination. Forms a complex with MYCBP2 and SKP1 but does not appear to form an authentic SCF (SKP1-CUL1-F-box protein) complex. Interacts (via B30.2/SPRY domain) with TP73 (via SAM domain); leading to its ubiquitination and degradation (By similarity). Interacts (via SRY domain) with UNC13A; leading to its degradation by the proteasome. Expressed speciffically in the central nervous system, including cerebellum, medulla oblongata, olfactory bulb, hippocampus, cortex and brain stem. Homozygous animals die soon after birth due to respiratory distress. Embryos show abnormal innervation of the diaphragm, impaired synapse formation at neuromuscular junctions, and aberrant development of axon fiber tracts in the brain. Belongs to the FBXO45/Fsn family.