Acyl-CoA synthetase (ACS4) is an arachidonate preferring acyl-CoA synthetase and has been shown to play an important role in lipid metabolism. Although arachidonate and decosahexanoate play a key role in lipid metabolism and in the brain, the mechanisms of its action are still not clearly understood. In this study, we identified brain-type ACS4 mRNA by 5'-RACE. We also confirmed that the mRNA in TT2 ES cells encoded a novel ACS4 protein, which contains 41 amino acids at its N-terminus. Furthermore, we found that ACS4 proteins were up-regulated in PC-12 cell by stimulation with nerve growth factor (NGF). Importantly, knockout of ACS4 in ES cells markedly attenuated neuronal differentiation induced by NGF and all-trans retinoic acids (RA). These results indicate that the ACS4 protein specifically expressed in brain plays an important role in arachidonate metabolism and neuronal differentiation in the brain. (C) 2012 Elsevier Inc. All rights reserved.