DLL4, expressed on a neighboring cell, binds NOTCH2 receptor and activates NOTCH2 intracellular signaling. The study used recombinant NOTCH2 and DLL4, exogenously expressed in Chinese hamster ovary cells. The species origin of NOTCH2 and DLL4 is not specified in the manuscript by Ji et al. 2004. The impact of fringe-mediated modification of NOTCH2 on activation by DLL4 has not been examined.