Target-derived survival factor for peripheral sensory sympathetic neurons (PubMed:1742028). May promote ameloblast differentiation and subsequent reduction in proliferation of ameloblasts (By similarity). {ECO:0000250|UniProtKB:Q80VU4, ECO:0000269|PubMed:1742028}. This is the function of ENSG00000225950 (NTF4, neurotrophin 4).