Plays multiple roles in neural tissues, regulates neuronal proliferation, survival, differentiation, polarization, as well as axon guidance and synaptic functions. Plays an important role in axon development during neuronal differentiation through the MAPK intracellular signaling pathway (By similarity). Via binding to its receptor ROBO3, plays a role in axon guidance, functioning as a repulsive axon guidance cue that contributes to commissural axon guidance to the midline (PubMed:32198364). Required for neuron survival through the modulation of MAPK signaling pathways too. Involved in the regulation of hypothalamic GNRH secretion and the control of puberty (By similarity). {ECO:0000250|UniProtKB:Q62918, ECO:0000269|PubMed:32198364}. Epididymal-secreted protein that signals through a ROS1- pathway to regulate the epididymal initial segment (IS) maturation, sperm maturation and male fertility. . This is the function of NELL2 (neural EGFL like 2, Ensembl gene identifier ENSG00000184613).